SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: el mojado on July 01, 2015, 07:12:03 AM
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Ok. I hope this is the last time I have to ask. After speaking extensively w engine builder, it seems like I'm going with a comp cam 268 ah. Part number K11-306-4. The complete kit.
20.5 70s Carribbean mini cruiser. 454, 10.5 comp, 750 vac sec, air gap, 049 heads (stock), MSD 6A ignition and dizzy, aluminum mercruiser center rise exhaust manifolds, jacuzzi wj ( not sure of impeller but tag says "B"). What are your opinions? Is this a good choice? What are the mini cruiser guys running?
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Not trying to come off as a dick... BUT... if you trust your engine builder, then trust your engine builder. If he says, "This is what we are going with..." then give him the benefit of the doubt that he may know something.
That all being said... it should be fine... not really the ideal choice (IMO)... but realistically, considering your not really optimizing the build to it's potential, you could be a little off on the cam and the boat would never really notice the difference. The one point of concern I have is the 10.5:1 compression with a short cam and a heavier boat... may have some detonation issues.
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Ok. I hope this is the last time I have to ask. After speaking extensively w engine builder, it seems like I'm going with a comp cam 268 ah. Part number K11-306-4. The complete kit.
20.5 70s Carribbean mini cruiser. 454, 10.5 comp, 750 vac sec, air gap, 049 heads (stock), MSD 6A ignition and dizzy, aluminum mercruiser center rise exhaust manifolds, jacuzzi wj ( not sure of impeller but tag says "B"). What are your opinions? Is this a good choice? What are the mini cruiser guys running?
You need to think the build backwards.
Let me explain.
The engine you describe is extremely mild. This engine is what I would consider to be virtually the same as a stock marine engine. Maybe 350 HP.
All that being said, what are you trying to do?
Do you want a 55mph, bulletproof cruiser? If yes, continue on. You will be fine.
Are your expectations to turn 5,500 rpm and be comfortable at 65 mph? If so, your about 150hp short. (IMO).
The vacuum secondary carburetor and the Air Gap intake Is a strange choice. (Again IMO) it's a mismatch of parts.
With the cam and exhaust system you have, I would have felt better with a Performer RPM.
I agree with putting some trust in the engine builder, that being said, how many jet boat motors has this cat built and did they stay built?
Make sure the valve stem to guides are set up "loose", use good intake valve stem seals and talk to him about piston to cylinder clearance.
Otherwise she sounds like a solid, very reliable build.
GT
Sent from my SCH-I545 using SoCal Jet Boats mobile app
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Ok. I hope this is the last time I have to ask. After speaking extensively w engine builder, it seems like I'm going with a comp cam 268 ah. Part number K11-306-4. The complete kit.
20.5 70s Carribbean mini cruiser. 454, 10.5 comp, 750 vac sec, air gap, 049 heads (stock), MSD 6A ignition and dizzy, aluminum mercruiser center rise exhaust manifolds, jacuzzi wj ( not sure of impeller but tag says "B"). What are your opinions? Is this a good choice? What are the mini cruiser guys running?
The WJ "B" impeller has a similar horsepower curve as the Berkeley "A" impeller. I have the chart somewhere.
With that combo, I'd up the duration @ .050" to ~230* and the lift around .575" to get some bark out of it.
My 454, very similar combo, no MSD, pulls a AA to 5K...thru logs and snails, and 9:1 comp. ratio. 87 octane.
I'd take advantage of the 10.5:1, don't cam it like a motorhome.
Dan'l
.
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I'd be happy w 55-60 max in my cruiser where i would be mostly cruising around 45. Id like to do the cam just once. I will never change to headers. Intake and carb can always be changed later. I just dont want to cut myself short with the cam
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I'd be happy w 55-60 max in my cruiser where i would be mostly cruising around 45. Id like to do the cam just once. I will never change to headers. Intake and carb can always be changed later. I just dont want to cut myself short with the cam
If you want to do it once, I would go one stage "up" and run a hydraulic roller.
It would make a gigantic difference.
JMHO
GT
Sent from my SCH-I545 using SoCal Jet Boats mobile app
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Roller is WAY out of budget
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Roller is WAY out of budget
I couldn't afford NOT to go roller...
You can't do a flat tappet twice for the price of a roller once.
Mine: http://www.summitracing.com/parts/hrs-cl120245-10/overview/make/chevrolet (http://www.summitracing.com/parts/hrs-cl120245-10/overview/make/chevrolet) $650
and it doesn't sound like a bayliner
Dan'l
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I couldn't afford NOT to go roller...
You can't do a flat tappet twice for the price of a roller once.
Mine: http://www.summitracing.com/parts/hrs-cl120245-10/overview/make/chevrolet (http://www.summitracing.com/parts/hrs-cl120245-10/overview/make/chevrolet) $650
and it doesn't sound like a bayliner
Dan'l
What pushrods did you use?
That looks like a pretty nice kit for the cash.
I would recommend going roller even if it's a stretch on the budget. It is one less headache and you can run virtually any automotive motor oil you want, saving you some money down the line. Probably a long payback, but piece of mind is worth a lot IMHO.
I just about lost it when I bought my mechanical roller and all the parts needed for the valve train, but I feel good knowing it will be bulletproof.
Not to mention, reusable to an extent.
I have slowly been building my 496 over the last two years. Money has been tight lately. (Very long story).
GT
Sent from my SCH-I545 using SoCal Jet Boats mobile app
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What pushrods did you use?
That looks like a pretty nice kit for the cash.
I would recommend going roller even if it's a stretch on the budget. It is one less headache and you can run virtually any automotive motor oil you want, saving you some money down the line. Probably a long payback, but piece of mind is worth a lot IMHO.
I just about lost it when I bought my mechanical roller and all the parts needed for the valve train, but I feel good knowing it will be bulletproof.
Not to mention, reusable to an extent.
I have slowly been building my 496 over the last two years. Money has been tight lately. (Very long story).
GT
Sent from my SCH-I545 using SoCal Jet Boats mobile app
Howards' pushrods 3/8", I think
Comp guide plates, 10* keepers and retainers.
Isky springs
summit double roller timing chain
crower stainless rockers
Delo 400 :)
Dan'l
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Howards' pushrods 3/8", I think
Comp guide plates, 10* keepers and retainers.
Isky springs
summit double roller timing chain
crower stainless rockers
Delo 400 :)
Dan'l
Nice.
GT
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Ok. I hope this is the last time I have to ask. After speaking extensively w engine builder, it seems like I'm going with a comp cam 268 ah. Part number K11-306-4. The complete kit.
20.5 70s Carribbean mini cruiser. 454, 10.5 comp, 750 vac sec, air gap, 049 heads (stock), MSD 6A ignition and dizzy, aluminum mercruiser center rise exhaust manifolds, jacuzzi wj ( not sure of impeller but tag says "B"). What are your opinions? Is this a good choice? What are the mini cruiser guys running?
I'm curious about what pistons you have to get 10.5cr with 049 heads.
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I'm curious about what pistons you have to get 10.5cr with 049 heads.
Speed pro piston H581CP .030 over. Summit catalog states these have -30 cc dome
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In my opinion you should drop your compression down to the 9.5 range and up the cam to the Comp Cams Extreme Marine 270H #K11-236-4 (if you insist on staying flat tappet).
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Pistons are already purchased and installed. Machine shop recommendation. Will the 270 still be a better choice
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Pistons are already purchased and installed. Machine shop recommendation. Will the 270 still be a better choice
Seems like you are getting some pretty good advice here - IMHO I would go up in the cam if you insist on 10.5 comp- A smaller cam will produce more static compression- Doing the math I attached your options to bring compression down. Even if you have to change the plan some, better to do it now than re-do later as stated before.
Here is some quick calculations with a .039 head gasket w 4.28 bore and 4.54 gasket bore- With the std marine gaskets you are closer to 11.1 - w/ 4.37 bore and .039
Heads are off, I'd have someone clean up and cc them- IMHO You'll probably produce more power where you need it and less likely to have detonation issues.
Hope it all works out for you!!
JW
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I settled on comp cam 270. I will talk to engine builder sbout going with thicker gaskets.
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First off different cam profiles WILL NOT change your static/mechanical compression ratio, only the dynamic compression. Second, this guy just doesn’t seem to trust his engine builder, for some reason and keeps asking questions on here second guessing the one who’s doing the work and or choosing the parts. Who knows maybe neither one of them know what they are doing. Thicker head gaskets are not a good choice; it’s a band aid to try and correct something that is wrong. With a G.M. style wedge shaped combustion chamber you have what’s called a quench area on the head as well as the piston. This is a combination of head gasket and deck clearance volume. To help atomize the fuel by way of turbulence on the compression stroke you really need to minimize this volume as much as possible so the piston’s quench surface is close to the head quench area. Not only will this help burn more of the fuel, it also holds off detonation. The flame front will not travel into this quench area during combustion, but this is where the end gases could ignite to cause the colliding flame fronts (detonation). Ugly things can happen within this area if the volume is large. If you choose someone to help you on a project you should follow their recommendations, if not, find someone else that really knows and pay them, before you have a trail of destruction and are out of a lot of money. I have read many of your posts, and it seems to me that you have already had some real rough times.
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I realize that too many cooks spoil the broth. I am not here trying to stir up anything, just crunching some numbers.
I would be seriously concerned about running a thicker head gasket because your Quench Distance is going to open up, making your engine more prone to detonation.
No disrespect to vintage240zracer, but I have never had good results using the online compression ratio calculators. I like to run the numbers the old fashioned way.
This is pure speculation based on numbers and my experience and NOT based on your actual parts. The only way to get accurate numbers is to measure the exact parts that will be used in your build.
Looking at your Speed-Pro H581CP30 pistons, they are advertised as having a 30cc dome and a 1.640 compression height. You really need to know your compression height, deck height, or amount milled from the deck surface to accurately calculate your compression ratio. Your block started out with a 9.8 deck height, connecting rod length is 6.135, and half of your 4.0” stroke is 2.0. Using the following numbers:
9.8 – 6.135 – 2.0 – 1.640 = .025
This means, unless your block has been decked, your Speed-Pro H581CP30 pistons will be “in the hole” as much as .025-inch. This volume adds as much as 5.894cc to the volume of the combustion chamber. This .025 in the hole combines with the gasket thickness to create the Quench Distance. The most commonly used Fel-Pro head gaskets have a compressed thickness of .039 and a volume of 9.700cc. If we use the factory blueprint numbers, the Quench Distance is .064
.039 + .025 = .064
I would make every effort to keep the Quench Distance UNDER .055 and everything I can find on the Big Block Chevy recommends a Quench Distance of .030 to .040. I think, in an open cooling system boat, you will need a little more clearance. I like Bostick’s recommendation, “Bore size, clearance, and application will dictate some variants in desired quench... but a general rule on a typical aspirated deal, .040-.045ish.”
Next, the heads are suspect to me. I am not sure where you came up with 116cc for combustion chamber volume. Without knowing the history of your heads, I can not be sure just how much material was removed during surfacing. My experience has been, combustion chambers always are on the high side of the advertised volume, making building compression difficult. This number depends on many variables such as; how much was surfaced off, how deep were the valve seats cut, shape of the valves, size of the valves, and any chamber work such as unshrouding of the valves. A few cc’s here and there doesn’t seem like much, but it all adds up, especially if you have an engine that is already compression challenged.
Here is what I come up with for numbers. I like to convert all dimensions to centimeters, that way all of my units are in cubic centimeters. To convert inches to centimeters, multiply by the constant 2.54. Yes, you can convert cubic inches into cubic centimeters by multiplying the ci by 16.387064. I also prefer to calculate area of a circle by using Pi * R^2
Bore: 4.280-inch 10.8712cm
Stroke: 4.0-inch 10.16cm
Deck Height: .025-inch 0.0635cm
Gasket Volume: 9.700cc
Piston Dome: 30cc
Combustion Chamber: 116cc
(((((10.8712/2)^2) * 3.1416) * 10.16) + ((((10.8712/2)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116) / (((((10.8712/2)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116)
(((((5.4356)^2) * 3.1416) * 10.16) + ((((5.4356)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116) / ((((5.4356)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116)
((((29.5457) * 3.1416) * 10.16) + (((29.5457) * 3.1416) * 0.0635) + 9.700 + (-30) + 116) / (((29.5457) * 3.1416) * 0.0635) + 9.700 + (-30) + 116)
((92.8207 * 10.16) + (92.8207 * 0.0635) + 9.700 + (-30) + 116) / ((92.8207 * 0.0635) + 9.700 + (-30) + 116)
(943.0583 + 5.8941 + 9.700 + (-30) + 116) / (5.8941 + 9.700 + (-30) + 116)
1044.6524 / 101.5941 = 10.2826
Using your numbers, your compression ratio is 10.28:1
Let’s assume that the deck height has been “zero decked” and the top of the pistons are flush with the top of the block. That bumps the compression ratio to 10.85:1.
If your block is decked so that your Quench Distance is per Bostick’s general recommendation of .040-.045, your compression ratio would range from 10.71:1 to 10.83:1.
All of these numbers assume that the volume of your heads is actually 116cc. Should you actually have 119cc combustion chambers, you would have 10.01:1 compression instead of 10.28:1. If your numbers are a little more conservative, and you actually have 113cc combustion chambers, you would have 10.57:1 compression instead of 10.28:1.
These examples should illustrate how the few unknown variables can influence your static compression ratio.
I use a program that I developed in SolidWorks to help me calculate dynamic compression ratio, which is influenced by cam timing, specifically intake valve closing point. While using the static compression ratio of 10.28:1, comparing the two cams that are mentioned in this thread, the 268AH http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=408&sb=2 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=408&sb=2) and the XM270H http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=404&sb=2 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=404&sb=2)
With the 268AH installed 4-degrees advanced (106* Intake Centerline) per CompCams recommendations, your engine would have a dynamic stroke of 3.250 inches and a dynamic compression ratio of 8.54:1
With the 268AH installed 2-degrees advanced (108* Intake Centerline) from CompCams recommendations, your engine would have a dynamic stroke of 3.199 inches and a dynamic compression ratio of 8.42:1
With the 268AH installed straight up (110* Intake Centerline), your engine would have a dynamic stroke of 3.146 inches and a dynamic compression ratio of 8.30:1
With these dynamic compression ratios, you are looking at detonation issues running premium pump gasoline.
With the XM270H installed 4-degrees advanced (108* Intake Centerline), your engine would have a dynamic stroke of 3.172 inches and a dynamic compression ratio of 8.36:1
With the XM270H installed 2-degrees advanced (110* Intake Centerline) per CompCams recommendations, your engine would have a dynamic stroke of 3.119 inches and a dynamic compression ratio of 8.24:1
With the XM270H installed straight up (112* Intake Centerline), your engine would have a dynamic stroke of 3.064 inches and a dynamic compression ratio of 8.11:1
Again, with these numbers, you are right on the edge of detonation and your tune will have to be right on the money. I would install the XM270H cam straight up at 112-degree intake centerline to favor the top end and reduce the dynamic compression ratio.
I would venture to recommend stepping up another cam size, reducing dynamic compression ratio further, to the XM278H http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=405&sb=0 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=405&sb=0)
With the XM278H installed 2-degrees advanced (110* Intake Centerline) per CompCams recommendations, your engine would have a dynamic stroke of 3.008 inches and a dynamic compression ratio of 7.98:1
With the XM278H installed straight up (112* Intake Centerline), your engine would have a dynamic stroke of 2.950 inches and a dynamic compression ratio of 7.85:1
I would install this cam on a 110 degree intake centerline (advanced 2 degrees), per CompCams recommendations, to favor bottom end in the event that you plan on pulling skiers and tubes. Otherwise, I would install this straight up for top end and for a little more user friendly tune.
If you have read through all of this rambling, I am surprised. I am actually surprised that I typed all of this. Anyway, your machine shop should be able to provide you with your deck height and I am willing to CC your heads for you. Again, until you know the actual numbers, this is all just speculation. At least it can help you with an educated guess.
Cheers,
Joe
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First off different cam profiles WILL NOT change your static/mechanical compression ratio, only the dynamic compression. Second, this guy just doesn’t seem to trust his engine builder, for some reason and keeps asking questions on here second guessing the one who’s doing the work and or choosing the parts. Who knows maybe neither one of them know what they are doing. Thicker head gaskets are not a good choice; it’s a band aid to try and correct something that is wrong. With a G.M. style wedge shaped combustion chamber you have what’s called a quench area on the head as well as the piston. This is a combination of head gasket and deck clearance volume. To help atomize the fuel by way of turbulence on the compression stroke you really need to minimize this volume as much as possible so the piston’s quench surface is close to the head quench area. Not only will this help burn more of the fuel, it also holds off detonation. The flame front will not travel into this quench area during combustion, but this is where the end gases could ignite to cause the colliding flame fronts (detonation). Ugly things can happen within this area if the volume is large. If you choose someone to help you on a project you should follow their recommendations, if not, find someone else that really knows and pay them, before you have a trail of destruction and are out of a lot of money. I have read many of your posts, and it seems to me that you have already had some real rough times.
Keep'n it real! :thumbup:
But since I already spent all that time crunching the numbers and typing it... :banghead:
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Hey look, someone that knows WTF their talking about…LOL…Hi Joe Great info Joe, I was thinking about really going in depth with this, but then thought no way, too many unknown variables, plus some would understand but again many wouldn’t. I have read a lot of posts on here, some I will comment on and some it’s just not worth my time or effort because you can tell they most likely won’t take your advice for one reason or another but most of the time you can tell when someone is trying to put something together with no “real” budget. That’s where a lot of people run into problems because of the parts they choose and also someone else is blowing bad advice in their ear....I always keep it real... :thumbup:
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I realize that too many cooks spoil the broth. I am not here trying to stir up anything, just crunching some numbers.
I would be seriously concerned about running a thicker head gasket because your Quench Distance is going to open up, making your engine more prone to detonation.
No disrespect to vintage240zracer, but I have never had good results using the online compression ratio calculators. I like to run the numbers the old fashioned way.
This is pure speculation based on numbers and my experience and NOT based on your actual parts. The only way to get accurate numbers is to measure the exact parts that will be used in your build.
Looking at your Speed-Pro H581CP30 pistons, they are advertised as having a 30cc dome and a 1.640 compression height. You really need to know your compression height, deck height, or amount milled from the deck surface to accurately calculate your compression ratio. Your block started out with a 9.8 deck height, connecting rod length is 6.135, and half of your 4.0” stroke is 2.0. Using the following numbers:
9.8 – 6.135 – 2.0 – 1.640 = .025
This means, unless your block has been decked, your Speed-Pro H581CP30 pistons will be “in the hole” as much as .025-inch. This volume adds as much as 5.894cc to the volume of the combustion chamber. This .025 in the hole combines with the gasket thickness to create the Quench Distance. The most commonly used Fel-Pro head gaskets have a compressed thickness of .039 and a volume of 9.700cc. If we use the factory blueprint numbers, the Quench Distance is .064
.039 + .025 = .064
I would make every effort to keep the Quench Distance UNDER .055 and everything I can find on the Big Block Chevy recommends a Quench Distance of .030 to .040. I think, in an open cooling system boat, you will need a little more clearance. I like Bostick’s recommendation, “Bore size, clearance, and application will dictate some variants in desired quench... but a general rule on a typical aspirated deal, .040-.045ish.”
Next, the heads are suspect to me. I am not sure where you came up with 116cc for combustion chamber volume. Without knowing the history of your heads, I can not be sure just how much material was removed during surfacing. My experience has been, combustion chambers always are on the high side of the advertised volume, making building compression difficult. This number depends on many variables such as; how much was surfaced off, how deep were the valve seats cut, shape of the valves, size of the valves, and any chamber work such as unshrouding of the valves. A few cc’s here and there doesn’t seem like much, but it all adds up, especially if you have an engine that is already compression challenged.
Here is what I come up with for numbers. I like to convert all dimensions to centimeters, that way all of my units are in cubic centimeters. To convert inches to centimeters, multiply by the constant 2.54. Yes, you can convert cubic inches into cubic centimeters by multiplying the ci by 16.387064. I also prefer to calculate area of a circle by using Pi * R^2
Bore: 4.280-inch 10.8712cm
Stroke: 4.0-inch 10.16cm
Deck Height: .025-inch 0.0635cm
Gasket Volume: 9.700cc
Piston Dome: 30cc
Combustion Chamber: 116cc
(((((10.8712/2)^2) * 3.1416) * 10.16) + ((((10.8712/2)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116) / (((((10.8712/2)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116)
(((((5.4356)^2) * 3.1416) * 10.16) + ((((5.4356)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116) / ((((5.4356)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116)
((((29.5457) * 3.1416) * 10.16) + (((29.5457) * 3.1416) * 0.0635) + 9.700 + (-30) + 116) / (((29.5457) * 3.1416) * 0.0635) + 9.700 + (-30) + 116)
((92.8207 * 10.16) + (92.8207 * 0.0635) + 9.700 + (-30) + 116) / ((92.8207 * 0.0635) + 9.700 + (-30) + 116)
(943.0583 + 5.8941 + 9.700 + (-30) + 116) / (5.8941 + 9.700 + (-30) + 116)
1044.6524 / 101.5941 = 10.2826
Using your numbers, your compression ratio is 10.28:1
Let’s assume that the deck height has been “zero decked” and the top of the pistons are flush with the top of the block. That bumps the compression ratio to 10.85:1.
If your block is decked so that your Quench Distance is per Bostick’s general recommendation of .040-.045, your compression ratio would range from 10.71:1 to 10.83:1.
All of these numbers assume that the volume of your heads is actually 116cc. Should you actually have 119cc combustion chambers, you would have 10.01:1 compression instead of 10.28:1. If your numbers are a little more conservative, and you actually have 113cc combustion chambers, you would have 10.57:1 compression instead of 10.28:1.
These examples should illustrate how the few unknown variables can influence your static compression ratio.
I use a program that I developed in SolidWorks to help me calculate dynamic compression ratio, which is influenced by cam timing, specifically intake valve closing point. While using the static compression ratio of 10.28:1, comparing the two cams that are mentioned in this thread, the 268AH http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=408&sb=2 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=408&sb=2) and the XM270H http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=404&sb=2 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=404&sb=2)
With the 268AH installed 4-degrees advanced (106* Intake Centerline) per CompCams recommendations, your engine would have a dynamic stroke of 3.250 inches and a dynamic compression ratio of 8.54:1
With the 268AH installed 2-degrees advanced (108* Intake Centerline) from CompCams recommendations, your engine would have a dynamic stroke of 3.199 inches and a dynamic compression ratio of 8.42:1
With the 268AH installed straight up (110* Intake Centerline), your engine would have a dynamic stroke of 3.146 inches and a dynamic compression ratio of 8.30:1
With these dynamic compression ratios, you are looking at detonation issues running premium pump gasoline.
With the XM270H installed 4-degrees advanced (108* Intake Centerline), your engine would have a dynamic stroke of 3.172 inches and a dynamic compression ratio of 8.36:1
With the XM270H installed 2-degrees advanced (110* Intake Centerline) per CompCams recommendations, your engine would have a dynamic stroke of 3.119 inches and a dynamic compression ratio of 8.24:1
With the XM270H installed straight up (112* Intake Centerline), your engine would have a dynamic stroke of 3.064 inches and a dynamic compression ratio of 8.11:1
Again, with these numbers, you are right on the edge of detonation and your tune will have to be right on the money. I would install the XM270H cam straight up at 112-degree intake centerline to favor the top end and reduce the dynamic compression ratio.
I would venture to recommend stepping up another cam size, reducing dynamic compression ratio further, to the XM278H http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=405&sb=0 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=405&sb=0)
With the XM278H installed 2-degrees advanced (110* Intake Centerline) per CompCams recommendations, your engine would have a dynamic stroke of 3.008 inches and a dynamic compression ratio of 7.98:1
With the XM278H installed straight up (112* Intake Centerline), your engine would have a dynamic stroke of 2.950 inches and a dynamic compression ratio of 7.85:1
I would install this cam on a 110 degree intake centerline (advanced 2 degrees), per CompCams recommendations, to favor bottom end in the event that you plan on pulling skiers and tubes. Otherwise, I would install this straight up for top end and for a little more user friendly tune.
If you have read through all of this rambling, I am surprised. I am actually surprised that I typed all of this. Anyway, your machine shop should be able to provide you with your deck height and I am willing to CC your heads for you. Again, until you know the actual numbers, this is all just speculation. At least it can help you with an educated guess.
Cheers,
Joe
Joe, Just want to take a minute to thank you for making some of my previous posts seem lacking as far as information. This is awesome, And I like where it ended up.... Still say shit-can the flat tappet and blow the rent money on a roller...
GT
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Joe, Just want to take a minute to thank you for making some of my previous posts seem lacking as far as information. This is awesome, And I like where it ended up.... Still say shit-can the flat tappet and blow the rent money on a roller...
GT
Indeed!
No balls, no glory!
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I realize that too many cooks spoil the broth. I am not here trying to stir up anything, just crunching some numbers.
I would be seriously concerned about running a thicker head gasket because your Quench Distance is going to open up, making your engine more prone to detonation.
No disrespect to vintage240zracer, but I have never had good results using the online compression ratio calculators. I like to run the numbers the old fashioned way.
This is pure speculation based on numbers and my experience and NOT based on your actual parts. The only way to get accurate numbers is to measure the exact parts that will be used in your build.
Looking at your Speed-Pro H581CP30 pistons, they are advertised as having a 30cc dome and a 1.640 compression height. You really need to know your compression height, deck height, or amount milled from the deck surface to accurately calculate your compression ratio. Your block started out with a 9.8 deck height, connecting rod length is 6.135, and half of your 4.0” stroke is 2.0. Using the following numbers:
9.8 – 6.135 – 2.0 – 1.640 = .025
This means, unless your block has been decked, your Speed-Pro H581CP30 pistons will be “in the hole” as much as .025-inch. This volume adds as much as 5.894cc to the volume of the combustion chamber. This .025 in the hole combines with the gasket thickness to create the Quench Distance. The most commonly used Fel-Pro head gaskets have a compressed thickness of .039 and a volume of 9.700cc. If we use the factory blueprint numbers, the Quench Distance is .064
.039 + .025 = .064
I would make every effort to keep the Quench Distance UNDER .055 and everything I can find on the Big Block Chevy recommends a Quench Distance of .030 to .040. I think, in an open cooling system boat, you will need a little more clearance. I like Bostick’s recommendation, “Bore size, clearance, and application will dictate some variants in desired quench... but a general rule on a typical aspirated deal, .040-.045ish.”
Next, the heads are suspect to me. I am not sure where you came up with 116cc for combustion chamber volume. Without knowing the history of your heads, I can not be sure just how much material was removed during surfacing. My experience has been, combustion chambers always are on the high side of the advertised volume, making building compression difficult. This number depends on many variables such as; how much was surfaced off, how deep were the valve seats cut, shape of the valves, size of the valves, and any chamber work such as unshrouding of the valves. A few cc’s here and there doesn’t seem like much, but it all adds up, especially if you have an engine that is already compression challenged.
Here is what I come up with for numbers. I like to convert all dimensions to centimeters, that way all of my units are in cubic centimeters. To convert inches to centimeters, multiply by the constant 2.54. Yes, you can convert cubic inches into cubic centimeters by multiplying the ci by 16.387064. I also prefer to calculate area of a circle by using Pi * R^2
Bore: 4.280-inch 10.8712cm
Stroke: 4.0-inch 10.16cm
Deck Height: .025-inch 0.0635cm
Gasket Volume: 9.700cc
Piston Dome: 30cc
Combustion Chamber: 116cc
(((((10.8712/2)^2) * 3.1416) * 10.16) + ((((10.8712/2)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116) / (((((10.8712/2)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116)
(((((5.4356)^2) * 3.1416) * 10.16) + ((((5.4356)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116) / ((((5.4356)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116)
((((29.5457) * 3.1416) * 10.16) + (((29.5457) * 3.1416) * 0.0635) + 9.700 + (-30) + 116) / (((29.5457) * 3.1416) * 0.0635) + 9.700 + (-30) + 116)
((92.8207 * 10.16) + (92.8207 * 0.0635) + 9.700 + (-30) + 116) / ((92.8207 * 0.0635) + 9.700 + (-30) + 116)
(943.0583 + 5.8941 + 9.700 + (-30) + 116) / (5.8941 + 9.700 + (-30) + 116)
1044.6524 / 101.5941 = 10.2826
Using your numbers, your compression ratio is 10.28:1
Let’s assume that the deck height has been “zero decked” and the top of the pistons are flush with the top of the block. That bumps the compression ratio to 10.85:1.
If your block is decked so that your Quench Distance is per Bostick’s general recommendation of .040-.045, your compression ratio would range from 10.71:1 to 10.83:1.
All of these numbers assume that the volume of your heads is actually 116cc. Should you actually have 119cc combustion chambers, you would have 10.01:1 compression instead of 10.28:1. If your numbers are a little more conservative, and you actually have 113cc combustion chambers, you would have 10.57:1 compression instead of 10.28:1.
These examples should illustrate how the few unknown variables can influence your static compression ratio.
I use a program that I developed in SolidWorks to help me calculate dynamic compression ratio, which is influenced by cam timing, specifically intake valve closing point. While using the static compression ratio of 10.28:1, comparing the two cams that are mentioned in this thread, the 268AH http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=408&sb=2 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=408&sb=2) and the XM270H http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=404&sb=2 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=404&sb=2)
With the 268AH installed 4-degrees advanced (106* Intake Centerline) per CompCams recommendations, your engine would have a dynamic stroke of 3.250 inches and a dynamic compression ratio of 8.54:1
With the 268AH installed 2-degrees advanced (108* Intake Centerline) from CompCams recommendations, your engine would have a dynamic stroke of 3.199 inches and a dynamic compression ratio of 8.42:1
With the 268AH installed straight up (110* Intake Centerline), your engine would have a dynamic stroke of 3.146 inches and a dynamic compression ratio of 8.30:1
With these dynamic compression ratios, you are looking at detonation issues running premium pump gasoline.
With the XM270H installed 4-degrees advanced (108* Intake Centerline), your engine would have a dynamic stroke of 3.172 inches and a dynamic compression ratio of 8.36:1
With the XM270H installed 2-degrees advanced (110* Intake Centerline) per CompCams recommendations, your engine would have a dynamic stroke of 3.119 inches and a dynamic compression ratio of 8.24:1
With the XM270H installed straight up (112* Intake Centerline), your engine would have a dynamic stroke of 3.064 inches and a dynamic compression ratio of 8.11:1
Again, with these numbers, you are right on the edge of detonation and your tune will have to be right on the money. I would install the XM270H cam straight up at 112-degree intake centerline to favor the top end and reduce the dynamic compression ratio.
I would venture to recommend stepping up another cam size, reducing dynamic compression ratio further, to the XM278H http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=405&sb=0 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=405&sb=0)
With the XM278H installed 2-degrees advanced (110* Intake Centerline) per CompCams recommendations, your engine would have a dynamic stroke of 3.008 inches and a dynamic compression ratio of 7.98:1
With the XM278H installed straight up (112* Intake Centerline), your engine would have a dynamic stroke of 2.950 inches and a dynamic compression ratio of 7.85:1
I would install this cam on a 110 degree intake centerline (advanced 2 degrees), per CompCams recommendations, to favor bottom end in the event that you plan on pulling skiers and tubes. Otherwise, I would install this straight up for top end and for a little more user friendly tune.
If you have read through all of this rambling, I am surprised. I am actually surprised that I typed all of this. Anyway, your machine shop should be able to provide you with your deck height and I am willing to CC your heads for you. Again, until you know the actual numbers, this is all just speculation. At least it can help you with an educated guess.
Cheers,
Joe
Well, I know who I'll have build my next motor hahahah
VERY good info, in a way, broken down into "lamens terms"
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I read all these posts. Thanks for the time guys. And yes its true i initially tried to save a buck the first time. No bueno. But now I am trying to get all the correct parts. But there is no way i can get a full roller. I talked to engine guy about cam selection and initially was trying to go conservative. He talked about the pros and cons of different cams and the 270 is where he thought it would do what I am asking for. So I'll see how it goes.
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Well, I know who I'll have build my next motor hahahah
VERY good info, in a way, broken down into "lamens terms"
Thank you, I'm just trying to make better decisions.
The best approach I have ever heard for engine building is:
1. Select a displacement that is suitable for the desired power level
2. Select a cylinder head with appropriate cross-sectional area and flow to support said displacement at the desired RPM
3. Select a cam with appropriate timing events to achieve the desired RPM
4. Select a static compression ratio that will provide the desired dynamic compression ratio according to the cam timing events
5. Fine tune the dynamic compression ratio with cam timing
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Everyone should have this thread in their "bookmark" list for future reference. Joe has pointed out some very usable information that should be retained.
Thanks Joe.
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Everyone should have this thread in their "bookmark" list for future reference. Joe has pointed out some very usable information that should be retained.
Thanks Joe.
Agreed...Thank you, I'm just trying to make better decisions.
The best approach I have ever heard for engine building is:
1. Select a displacement that is suitable for the desired power level
2. Select a cylinder head with appropriate cross-sectional area and flow to support said displacement at the desired RPM
3. Select a cam with appropriate timing events to achieve the desired RPM
4. Select a static compression ratio that will provide the desired dynamic compression ratio according to the cam timing events
5. Fine tune the dynamic compression ratio with cam timing
One word of caution on this information.
One goofy thing that comes up on a jet boat engine that separates them from all others is the linear torque load. Acceleration will literally cease when the required torque drops off, it's not "running out of air" like most people think, it just simply does not have the negative intake pressure to pull in any more... This is where carburetor selection and intake type gets so convoluted... Trying to get a Stoichiometric fuel charge on a high horse jet at WOT is IMHO the hard part.
In other words, the CFM calculation for a car cannot be used.
Great stuff...
GT
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I realize that too many cooks spoil the broth. I am not here trying to stir up anything, just crunching some numbers.
I would be seriously concerned about running a thicker head gasket because your Quench Distance is going to open up, making your engine more prone to detonation.
No disrespect to vintage240zracer, but I have never had good results using the online compression ratio calculators. I like to run the numbers the old fashioned way.
This is pure speculation based on numbers and my experience and NOT based on your actual parts. The only way to get accurate numbers is to measure the exact parts that will be used in your build.
Looking at your Speed-Pro H581CP30 pistons, they are advertised as having a 30cc dome and a 1.640 compression height. You really need to know your compression height, deck height, or amount milled from the deck surface to accurately calculate your compression ratio. Your block started out with a 9.8 deck height, connecting rod length is 6.135, and half of your 4.0” stroke is 2.0. Using the following numbers:
9.8 – 6.135 – 2.0 – 1.640 = .025
This means, unless your block has been decked, your Speed-Pro H581CP30 pistons will be “in the hole” as much as .025-inch. This volume adds as much as 5.894cc to the volume of the combustion chamber. This .025 in the hole combines with the gasket thickness to create the Quench Distance. The most commonly used Fel-Pro head gaskets have a compressed thickness of .039 and a volume of 9.700cc. If we use the factory blueprint numbers, the Quench Distance is .064
.039 + .025 = .064
I would make every effort to keep the Quench Distance UNDER .055 and everything I can find on the Big Block Chevy recommends a Quench Distance of .030 to .040. I think, in an open cooling system boat, you will need a little more clearance. I like Bostick’s recommendation, “Bore size, clearance, and application will dictate some variants in desired quench... but a general rule on a typical aspirated deal, .040-.045ish.”
Next, the heads are suspect to me. I am not sure where you came up with 116cc for combustion chamber volume. Without knowing the history of your heads, I can not be sure just how much material was removed during surfacing. My experience has been, combustion chambers always are on the high side of the advertised volume, making building compression difficult. This number depends on many variables such as; how much was surfaced off, how deep were the valve seats cut, shape of the valves, size of the valves, and any chamber work such as unshrouding of the valves. A few cc’s here and there doesn’t seem like much, but it all adds up, especially if you have an engine that is already compression challenged.
Here is what I come up with for numbers. I like to convert all dimensions to centimeters, that way all of my units are in cubic centimeters. To convert inches to centimeters, multiply by the constant 2.54. Yes, you can convert cubic inches into cubic centimeters by multiplying the ci by 16.387064. I also prefer to calculate area of a circle by using Pi * R^2
Bore: 4.280-inch 10.8712cm
Stroke: 4.0-inch 10.16cm
Deck Height: .025-inch 0.0635cm
Gasket Volume: 9.700cc
Piston Dome: 30cc
Combustion Chamber: 116cc
(((((10.8712/2)^2) * 3.1416) * 10.16) + ((((10.8712/2)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116) / (((((10.8712/2)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116)
(((((5.4356)^2) * 3.1416) * 10.16) + ((((5.4356)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116) / ((((5.4356)^2) * 3.1416) * 0.0635) + 9.700 + (-30) + 116)
((((29.5457) * 3.1416) * 10.16) + (((29.5457) * 3.1416) * 0.0635) + 9.700 + (-30) + 116) / (((29.5457) * 3.1416) * 0.0635) + 9.700 + (-30) + 116)
((92.8207 * 10.16) + (92.8207 * 0.0635) + 9.700 + (-30) + 116) / ((92.8207 * 0.0635) + 9.700 + (-30) + 116)
(943.0583 + 5.8941 + 9.700 + (-30) + 116) / (5.8941 + 9.700 + (-30) + 116)
1044.6524 / 101.5941 = 10.2826
Using your numbers, your compression ratio is 10.28:1
Let’s assume that the deck height has been “zero decked” and the top of the pistons are flush with the top of the block. That bumps the compression ratio to 10.85:1.
If your block is decked so that your Quench Distance is per Bostick’s general recommendation of .040-.045, your compression ratio would range from 10.71:1 to 10.83:1.
All of these numbers assume that the volume of your heads is actually 116cc. Should you actually have 119cc combustion chambers, you would have 10.01:1 compression instead of 10.28:1. If your numbers are a little more conservative, and you actually have 113cc combustion chambers, you would have 10.57:1 compression instead of 10.28:1.
These examples should illustrate how the few unknown variables can influence your static compression ratio.
I use a program that I developed in SolidWorks to help me calculate dynamic compression ratio, which is influenced by cam timing, specifically intake valve closing point. While using the static compression ratio of 10.28:1, comparing the two cams that are mentioned in this thread, the 268AH http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=408&sb=2 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=408&sb=2) and the XM270H http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=404&sb=2 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=404&sb=2)
With the 268AH installed 4-degrees advanced (106* Intake Centerline) per CompCams recommendations, your engine would have a dynamic stroke of 3.250 inches and a dynamic compression ratio of 8.54:1
With the 268AH installed 2-degrees advanced (108* Intake Centerline) from CompCams recommendations, your engine would have a dynamic stroke of 3.199 inches and a dynamic compression ratio of 8.42:1
With the 268AH installed straight up (110* Intake Centerline), your engine would have a dynamic stroke of 3.146 inches and a dynamic compression ratio of 8.30:1
With these dynamic compression ratios, you are looking at detonation issues running premium pump gasoline.
With the XM270H installed 4-degrees advanced (108* Intake Centerline), your engine would have a dynamic stroke of 3.172 inches and a dynamic compression ratio of 8.36:1
With the XM270H installed 2-degrees advanced (110* Intake Centerline) per CompCams recommendations, your engine would have a dynamic stroke of 3.119 inches and a dynamic compression ratio of 8.24:1
With the XM270H installed straight up (112* Intake Centerline), your engine would have a dynamic stroke of 3.064 inches and a dynamic compression ratio of 8.11:1
Again, with these numbers, you are right on the edge of detonation and your tune will have to be right on the money. I would install the XM270H cam straight up at 112-degree intake centerline to favor the top end and reduce the dynamic compression ratio.
I would venture to recommend stepping up another cam size, reducing dynamic compression ratio further, to the XM278H http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=405&sb=0 (http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=405&sb=0)
With the XM278H installed 2-degrees advanced (110* Intake Centerline) per CompCams recommendations, your engine would have a dynamic stroke of 3.008 inches and a dynamic compression ratio of 7.98:1
With the XM278H installed straight up (112* Intake Centerline), your engine would have a dynamic stroke of 2.950 inches and a dynamic compression ratio of 7.85:1
I would install this cam on a 110 degree intake centerline (advanced 2 degrees), per CompCams recommendations, to favor bottom end in the event that you plan on pulling skiers and tubes. Otherwise, I would install this straight up for top end and for a little more user friendly tune.
If you have read through all of this rambling, I am surprised. I am actually surprised that I typed all of this. Anyway, your machine shop should be able to provide you with your deck height and I am willing to CC your heads for you. Again, until you know the actual numbers, this is all just speculation. At least it can help you with an educated guess.
Cheers,
Joe
And this is why I am not at all butt-hurt by being corrected by these folks- No disrespect taken Joe! Again they know what they are talking about- Just trying to gives options and not knowing exactly what the machinist is doing, tried to give him some rough numbers- There are better calculators for sure!! ;) BBC are fairly new to me as far as building them for power and reliability. Experience with race Triumph motors and Nissan are my forte- Using different thickness gaskets is not uncommon for our race motors, since they are all custom made to spec, as Joe pointed out, it may cause issues in your application.
Good stuff here!
JW
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Experience with race Triumph motors and Nissan are my forte- Using different thickness gaskets is not uncommon for our race motors, since they are all custom made to spec, as Joe pointed out, it may cause issues in your application.
Good stuff here!
JW
Thank you. Aren't those hemispherical or pent-roof style combustion chambers? What gaskets are you using? Hope to make it out to watch you race soon.
Cheers,
Joe
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Everyone should have this thread in their "bookmark" list for future reference. Joe has pointed out some very usable information that should be retained.
Thanks Joe.
Thank you Keith and Glen for the kind words. I'm honored.
Joe
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As I look over this entire post, once again this thread has become entirely too in depth for this persons application again. No doubt, good info. But too much for the job at hand, I get what GT is saying about going roller, but don’t forget for a second that these cams can fail too, I have seen it many times in factory parts as well as aftermarket. These are not the “God send” of cams, nothing is fool proof. There are more moving parts with these set ups, most of the time it’s a lifter failure or I’ve even seen the hardened surface on the lobes go away. Yes one will spend about another $1,000 or more on a roller valvetrain when building an engine, but there also is no guarantee you will produce more power over a flat tappet grind. There are variables there too, talking of the specific valve timing events and lobe profile, it’s more than just friction reduction. To be certain both cams with almost identical valve timing and lobe profiles need to be run in that engine on a dyno, perhaps the roller will produce a slight bit more power, but you will never feel it in the seat.
Cam and valvetrain choice will always boil down to application, and for some people budget. I am still a big fan of flat tappet cams, both hydraulic and mechanical. I’ve had tremendous success with them and yes the oils and additives are still available for the protection needed. I’m also a fan of roller cams for when the application is also needed. I have been in a dyno cell when an NHRA stock eliminator 396ci engine is being tested with a solid flat tappet cam, this engine made incredible power all the way up into an RPM range where most will think that only a roller will survive, well that’s bullshit. For the owner of this boat, just shove that hydraulic bumpstick in, perform a proper break in and go play, your not building a competition engine for a drag boat.
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As I look over this entire post, once again this thread has become entirely too in depth for this persons application again. No doubt, good info. But too much for the job at hand, I get what GT is saying about going roller, but don’t forget for a second that these cams can fail too, I have seen it many times in factory parts as well as aftermarket. These are not the “God send” of cams, nothing is fool proof. There are more moving parts with these set ups, most of the time it’s a lifter failure or I’ve even seen the hardened surface on the lobes go away. Yes one will spend about another $1,000 or more on a roller valvetrain when building an engine, but there also is no guarantee you will produce more power over a flat tappet grind. There are variables there too, talking of the specific valve timing events and lobe profile, it’s more than just friction reduction. To be certain both cams with almost identical valve timing and lobe profiles need to be run in that engine on a dyno, perhaps the roller will produce a slight bit more power, but you will never feel it in the seat.
Cam and valvetrain choice will always boil down to application, and for some people budget. I am still a big fan of flat tappet cams, both hydraulic and mechanical. I’ve had tremendous success with them and yes the oils and additives are still available for the protection needed. I’m also a fan of roller cams for when the application is also needed. I have been in a dyno cell when an NHRA stock eliminator 396ci engine is being tested with a solid flat tappet cam, this engine made incredible power all the way up into an RPM range where most will think that only a roller will survive, well that’s bullshit. For the owner of this boat, just shove that hydraulic bumpstick in, perform a proper break in and go play, your not building a competition engine for a drag boat.
For me personally, going roller has very little to do with making good power over a flat.
It has to do more with overall engine life.
The three roller engines I have built in the last five years have proven to just be more durable and the proof is in the oil analysis results.
Roller engines are just cleaner.
I have witnessed a ratio of about 30 :1 when it comes to flat tappet failures to any roller failure. Normally a roller will kill a lifter, if caught in time, simple swap of one lifter. Try that on a flat tappet.
The valve train harmonics are also all but eliminated, this is easier on the rockers and valves.
Don't get me wrong. Flat cams work, but all things being equal, I would bet on the roller every time.
Great thread IMO
GT
Sent from my SCH-I545 using SoCal Jet Boats mobile app
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I do get ya GT, you have obviously been in the industry as long as I and have also seen a lot. But we both know usually (but not all) a direct link to a parts failure can be tied to how that part was maintained. Valvetrain harmonics will always be present with all cams, hydraulic cams are pretty forgiving though, what is hard on components is valve lash with the mechanical versions. I run a mechanical roller in my drag race engine in my dragster, over the years I have had two lifter failures that actually did lobe damage and I keep a watchful eye on all my parts, so you just never know, but that’s racing. I have a solid flat tappet in my BBC engine in my Chevelle that I built in 1992, I have never had a problem with it and it’s not a small cam either…Oh well…it is what it is I guess…It boils down to personal preference, application and budget…All is good.... :thumbup:
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I do get ya GT, you have obviously been in the industry as long as I and have also seen a lot. But we both know usually (but not all) a direct link to a parts failure can be tied to how that part was maintained. Valvetrain harmonics will always be present with all cams, hydraulic cams are pretty forgiving though, what is hard on components is valve lash with the mechanical versions. I run a mechanical roller in my drag race engine in my dragster, over the years I have had two lifter failures that actually did lobe damage and I keep a watchful eye on all my parts, so you just never know, but that’s racing. I have a solid flat tappet in my BBC engine in my Chevelle that I built in 1992, I have never had a problem with it and it’s not a small cam either…Oh well…it is what it is I guess…It boils down to personal preference, application and budget…All is good.... :thumbup:
Well that sure adds a different dynamic.
I'm from the marathon type racing, you are obviously from the straight and narrow world. (Take that as a compliment lol).
I would think (could be fos) that the difference would be a bit more extreme on something that runs hours at a time vs.something that runs for mere seconds.
Joe, what's your take.
No books bro... LMAO.
GT
Sent from my SCH-I545 using SoCal Jet Boats mobile app
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Yes I’m from more less the drag racing side of things, and I know from past readings more of your interest or exposure is from the endurance world with numerous laps or hours of operation. All is great and all is performance and racing, many concepts and components cross over. Even though drag racing engines run for a shorter time, they are still pushed hard and the parts take a hit. With both styles of motor sports sometimes class rules will dictate as to what can be used within an engine. But all out competition the choice is up to you, but there may be other restrictions on the car or boat. I know a marine engine can fall into an endurance application very easily, but with an engine that’s not that radical and being asked to do a specific job, I still feel that a flat tappet cam will still do the job just fine. That’s what I have chosen for my jet boat BBC engine, and I haven’t had so much as a hick up out of it since it was pulled off the engine dyno two years ago, and I run it pretty hard and it has a fair amount of time on it already running up and down the Colorado River along with participating in drag boat racing events just for shit’s and giggles, I have a lot of reliable turn key fun with it, but I’m not new to all of this either and know how to set things up correctly and maintain them if needed.
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Thank you. Aren't those hemispherical or pent-roof style combustion chambers? What gaskets are you using? Hope to make it out to watch you race soon.
Cheers,
Joe
The newer Jap stuff yea! the stuff I deal with is more traditional style chamber- though the BMW (2002) our competition is Hemi style. We have copper gaskets made for the Triumph stuff and use NISMO or Victor Reinz, Felpro is junk for the Turbo stuff and 14.1 race stuff in these applications.
JW
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Well that sure adds a different dynamic.
I'm from the marathon type racing, you are obviously from the straight and narrow world. (Take that as a compliment lol).
I would think (could be fos) that the difference would be a bit more extreme on something that runs hours at a time vs.something that runs for mere seconds.
Joe, what's your take.
No books bro... LMAO.
GT
First, I would say, for an end user in the position of, "I just want to enjoy my boat and not spend a fortune and all my vacation time wrenching on it," wether flat tappet or roller, I would definitely recommend a hydraulic.
One thing I haven't seen mentioned here is that solid rollers don't like idle time. Not a good thing in a cruiser.
I think taking the end user into consideration is important. Throwing out a comparison, building and engine for the OP vs RTCP, they are worlds apart and therefore will be built completely different. The OP isn't chasing triple digits. I would also wager that he won't enjoy the operating expenses associated with with a monster cam. I burned through over 100 gallons of fuel one weekend. Most wouldn't be down with that.
I will say, once I went roller, the whole demeanor of my engines changed. But this isn't about my boat.
Cheers,
Joe