SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: Ckaz21 on March 06, 2014, 08:24:00 PM
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Anyone no how much hp stock 049 heads will support without putting the bigger valves in? Machinist wants $500 in labor for installing bigger valves and that doesn't include parts! Might keep them as is.
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What is the rest of your combo?
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Dunno yet lol. Right now I have my 454 disassembled. I'm for sure going to throw in some comp pistons to get it to 10:1. Not sure on what cam to run. I think that the cam all depends on what I do with the heads. I might go aftermarket, that why I'm wonder how much hp the heads can flow. I know that stock they flow 270cfm on the intake but I have no Idea how much hp that will support.
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*high comp
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Let me put it to you like this.
Bigger is not always better. Build the motor to what you have.
It is my humble opinion that the $500 would be better spent elsewhere.
stock port matched 049 heads should have no strain getting into the 550-600 HP range if built the the existing valves, not sure you would get a huge gain with larger valves as they will not be the limiting factor.
Bigger valves are many times like great eyesight, nice to have, but if you don't have it, you can't see what you are missing. :o
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Mid 600s are entirely achievable NA. What kind of engine would you LIKE to build?
Might I suggest, if you go supercharged, you could push enough air through those heads to easily make well over 1,000HP. I would really suggest looking into a decent centrifugal. Dollar for dollar, you will make more HP supercharged than you will ever make with that engine and any aftermarket head naturally aspirated. No need for costly porting. And you will have a variable HP engine where you can change boost levels to suit your needs.
Could you please elaborate more on the vehicle for which this engine is destined?
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Bigger is not always better...
...they will not be the limiting factor.
X2
Bigger valves will also shroud more, unnecessarily.
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The engine is going in my jet boat. Its a berk jg with A impeller. Engine is the stock hardin marine 330hp 454. It has 049 heads though. I tore the engine apart cause 330hp isn't enough. I want to it 80mph this year. Guessing I'm going to need at least 550hp so I'm trying to get the engine in that range. I won't have enough cash to supercharge although that would be awesome. I have about a $2500 budget. I was thinking bore it 60 over. New pop up pistons, new cam(no idea which to get tho), new rods and maybe sell my 049 heads and get a set of after markets or keep them if you guys think they will support that much hp while be n/a...? Thanks in advance
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Additional info: Tahiti caribbean model 18ft
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You could bolt a weiend super charger on that thing for 1800 dollars and get just at 500 hp
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80 mph on 500 HP?
In a Tahiti?
How fast is it as is?
I think your goal is a little ambitious. Raise the HP or lower the mph.
JMHO. FWIW.
GT
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I'm not saying how fast I'm just saying by bolting on that Huffer on that stock motor he'll get 500 he out of it, I just wonder how long the bottom end will hold together.
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Actual dyno hp? Or internet hp?
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Realistically I think it'll need 600hp to hit 80mph. And yes I am looking for 550-600 dyno hp. Right now the boat is bone stock no loader or diverter and it only did 55mph at 4,200 rpm.
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To go from 55 mph to 80 your going to spend more the $2500.
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Why only 55? If the pump is good it should do 60? I have a heavy 18'. With my new impeller
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.. I'm hitting 65 upstream and my motor is pretty much "stock". I'm .030" over have a crower mild cam and a 750holly on top. Nothin crazy?
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Realistically I think it'll need 600hp to hit 80mph. And yes I am looking for 550-600 dyno hp. Right now the boat is bone stock no loader or diverter and it only did 55mph at 4,200 rpm.
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I just had to ask since a lot of people like to throw around big hp numbers for minimal effort like that shit is free or something. >:D
I'm gonna assume you're looking to build a pump gas friendly engine... more than likely in the upper 9:1- low10:1 range? And seeing that your budget is in the 2500 range... we'll rule out things like strokers, roller cams, and pretty much any more than bare bones machine work.
Realistically, on a pump gas build, with stock 2.065 and 1.72 valves, and just a slight port work, flat tapper, within the confines of what you have to work with, you will not see mid 600's with a 468... just not going to happen in reality... internet/ebay/craigslist perhaps, but not in your boat in an rpm range that you'll actually need to be working in. That would mean that you would need to make 1.4hp per inch... and a warmed over stocker ain't gonna get close to that... especially when designed to work in the upper 5k lower 6k rpm range. I'd say a more realistic goal within those parameters would be the 1.1-1.2ish range... and even then, you're gonna need to sharpen up your pencil and figure out a nice combo that works well together. Now, you wish to go with more head work, or add some compression, or roller, or a combo of all the above, and 600 on up is not a problem with 049 heads.
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Yeah I see what you guys are saying. Maybe I'll just buy a stroker kit and new cam for now. Then do the heads and maybe a better cam later on. Either way I'm getting it dynoed so I'll be sure to post the numbers with my combo.
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If your block is standard bore now and will clean up with .030 overbore; the performance gain from boring your block to the max is far outweighed by the reduction in life and rigidity.
On another note, in the pursuit of your 80 MPH goal, you should also focus on getting your boat to ride right as well as ensuring your pump is performing well.
Look at the system as a whole. The engine is just one part.
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I'm not saying how fast I'm just saying by bolting on that Huffer on that stock motor he'll get 500 he out of it, I just wonder how long the bottom end will hold together.
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rush1, I was using the below quote for the 80MPH
The engine is going in my jet boat. Its a berk jg with A impeller. Engine is the stock hardin marine 330hp 454. It has 049 heads though. I tore the engine apart cause 330hp isn't enough. I want to it 80mph this year. Guessing I'm going to need at least 550hp so I'm trying to get the engine in that range. I won't have enough cash to supercharge although that would be awesome. I have about a $2500 budget. I was thinking bore it 60 over. New pop up pistons, new cam(no idea which to get tho), new rods and maybe sell my 049 heads and get a set of after markets or keep them if you guys think they will support that much hp while be n/a...? Thanks in advance
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Ckaz21, I am not trying to criticize you.
Just want you to know that to get that hull to see 80mph is very, very optimistic. (please read impossible) with your $2500 budget, I don't care if you started with a 600 HP motor.
Here are the facts;
You have 330 HP and the boat does 55 MPH (for the record, something seems off with the math because your rpm range is pitiful).
Your boat is in full family trim (read "eating pork often").
It virtually costs $2500 do do a pretty straight forward rebuild, much less double the rated HP.
These are pretty hard for me to ignore.
I have an honest 85 MPH jet, it had roughly 650 HP at 5,200 RPM, extensive bottom work on the bottom of an already light (between 500 and 600 pounds) hull, extensive pump work, custom built loader, Place Diverter, stuffer plate, fiberglass bucket seat (2), no rear seat, two aluminum fuel tanks at less than 1/4 tank, 850 dp massaged to obtain 890 flow bench verified CFM at -1.5 "hg vacuum, MSD system 468 Chevy. The boat was a little hairy to drive, needed a droop very badly and had the last few feet of boat "wet" she was aired out to the point of scary.
With a boat twice as heavy, I would probably say that you will need to be in the mid 700's to even get close, this while turning about 5,500 RPM and be able to keep the pump loaded while at the same time, build some lift.
Tall order. :sly:
Lower your sights for 70+/- MPH and I can tell you how to get there, you are going to need to borrow about a grand though. ;)
Hope this puts things in perspective. Not trying to be a snotbag.
GT
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If your block is standard bore now and will clean up with .030 overbore; the performance gain from boring your block to the max is far outweighed by the reduction in life and rigidity.
On another note, in the pursuit of your 80 MPH goal, you should also focus on getting your boat to ride right as well as ensuring your pump is performing well.
Look at the system as a whole. The engine is just one part.
Sound words.
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Yeah I see what you guys are saying. Maybe I'll just buy a stroker kit and new cam for now. Then do the heads and maybe a better cam later on. Either way I'm getting it dynoed so I'll be sure to post the numbers with my combo.
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Building a stroker with limited cylinder head upgrades will definitely hurt you... JMHO
Be prepared to be disappointed, I know I sure was. :P Ever heard of the Central Oregon CCOC Automotive tech classes? Had an opportunity to work with a few students going there. This was a few years ago.
GT
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...I'm wonder how much hp the heads can flow. I know that stock they flow 270cfm on the intake but I have no Idea how much hp that will support.
Basically around 2 HP / CFM if the assembly and the combination are correct.
Just remember that there is more to making horsepower than peak flow numbers. Low lift flow for your application is going to be crucial. Look at the flow numbers at each lift point. Average flow up to the point of max lift of your cam should be considered. A smaller head with the same airflow as a larger head will have greater air/fuel velocity, will make more power, and be more responsive.
Here is a good start:
http://www.speedtalk.com/forum/viewtopic.php?f=1&t=29305 (http://www.speedtalk.com/forum/viewtopic.php?f=1&t=29305)
http://www.yellowbullet.com/forum/showthread.php?t=130614 (http://www.yellowbullet.com/forum/showthread.php?t=130614)
Interesting read:
http://www.superchevy.com/technical/engines_drivetrain/cams_heads_valvetrain/sucp_1206_oval_port_big_block_chevy_cylinder_heads/ (http://www.superchevy.com/technical/engines_drivetrain/cams_heads_valvetrain/sucp_1206_oval_port_big_block_chevy_cylinder_heads/)
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GT Jets,
I was scared someone was going to chime in about how heavy my boat is. I've owned 2 v-drives and 3 jets in my life and the tahiti that I have now is by far the heaviest. I heard it weighs 1,800 from the original magazine ad that I saw of it. With that being said I'll lower my expectations to low 70s. My engine had a flat cam so it wouldnt rev past 4,300 w/o popping and at that rpm it was hitting 54-55 mph on the gps. I'm already going to be getting a loader and diverter for it before summer so I am only concerned about the engine right now (pump was rebuilt a couple years ago). I'll try to save an extra grand so I'll have a budget of $3,500 for the engine. Only labor I'll need to pay for is machining and and dyno. I'll assemble it myself. Flusher, I def won't bore it 60 over then. I'll see if they can hone it first if not I'll go with 30 over. So with $3,500 to put in the engine what combo do you guys think I should go with? Cause now I'm stumped lol, it almost seems like unless you have 6gs to throw at it you might as well just do a stock rebuild.
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Weight plays a huge role in acceleration. The power to weight ratio is believed to be even more critical in a drag boat compared to that of a drag car. Either way, weight placement IS critical. You did not mention an ET goal or drag racing. Anyway, who am I to judge regarding heavy boats with my super-tanker-like 21’ Hallett.
The power needed to push an object through a fluid increases as the cube of the velocity. Bottom line, if you want to go faster, you have two choices. 1.) Build more horsepower. 2.) Reduce the amount of drag on your hull. I will focus on reducing the drag for a moment.
Aerodynamic and hydrodynamic forces are working against you. Weight placement is huge. Moving weight forward will allow the stern to rise out of the water when on plane, reducing drag. Moving the weight ahead of the center of gravity will cause the bow to plow through the water increasing drag.
Looking at your pictures, you are probably not interested in a stripped down drag boat with the engine moved 30-inches forward of the transom, however you do have some options, while keeping your family cruiser functional as just that. You can move items forward in your boat. It won’t have the same affect as scrapping your back seat and moving the engine forward, but it will make a difference and every little bit helps. For example, in my tug boat, the battery is mounted under the original rear seats and the fuel and oil filters were mounted on or near the transom. The transom seems to be a handy place to mount all kinds of ballast; from hydraulic trim pumps to stereo amps. Moving my engine forward is just not an option for me. All of that weight, right on the extreme rear of the boat all acts to keep the ass planted deep. Good for wakeboarding, but not so good for performance.
Your plan for aftermarket heads will help too by reducing aft weight and overall weight. After power-lifting a set of iron BBC heads around my shop today, it really makes me want to upgrade to aluminum.
Do you have a shoe and a ride plate? A back-cut shoe and ride plate will help to develop lift to get the whole boat out of the water, reducing drag. Yes, the shoe will create a little drag, but the overall net drag will be less because of the lift generated, reducing the wetted surface area. A back-cut shoe and ride plate will tend to lift the boat straight up and do nothing for attitude. Changing the nozzle angle will change the attitude, airing the boat out. You can change the nozzle angle with angle-shims or with a diverter.
Sorry to be long winded, but to summarize, getting your boat to ride right is a big part of achieving your speed goals. Not all of it has to cost money. Take a look at your weight distribution and think about what can be done to help that. You have what you have to work with, it is just time to start optimizing your configuration.
Cheers,
Joe
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Weight plays a huge role in acceleration. The power to weight ratio is believed to be even more critical in a drag boat compared to that of a drag car. Either way, weight placement IS critical. You did not mention an ET goal or drag racing. Anyway, who am I to judge regarding heavy boats with my super-tanker-like 21’ Hallett.
The power needed to push an object through a fluid increases as the cube of the velocity. Bottom line, if you want to go faster, you have two choices. 1.) Build more horsepower. 2.) Reduce the amount of drag on your hull. I will focus on reducing the drag for a moment.
Aerodynamic and hydrodynamic forces are working against you. Weight placement is huge. Moving weight forward will allow the stern to rise out of the water when on plane, reducing drag. Moving the weight ahead of the center of gravity will cause the bow to plow through the water increasing drag.
Looking at your pictures, you are probably not interested in a stripped down drag boat with the engine moved 30-inches forward of the transom, however you do have some options, while keeping your family cruiser functional as just that. You can move items forward in your boat. It won’t have the same affect as scrapping your back seat and moving the engine forward, but it will make a difference and every little bit helps. For example, in my tug boat, the battery is mounted under the original rear seats and the fuel and oil filters were mounted on or near the transom. The transom seems to be a handy place to mount all kinds of ballast; from hydraulic trim pumps to stereo amps. Moving my engine forward is just not an option for me. All of that weight, right on the extreme rear of the boat all acts to keep the ass planted deep. Good for wakeboarding, but not so good for performance.
Your plan for aftermarket heads will help too by reducing aft weight and overall weight. After power-lifting a set of iron BBC heads around my shop today, it really makes me want to upgrade to aluminum.
Do you have a shoe and a ride plate? A back-cut shoe and ride plate will help to develop lift to get the whole boat out of the water, reducing drag. Yes, the shoe will create a little drag, but the overall net drag will be less because of the lift generated, reducing the wetted surface area. A back-cut shoe and ride plate will tend to lift the boat straight up and do nothing for attitude. Changing the nozzle angle will change the attitude, airing the boat out. You can change the nozzle angle with angle-shims or with a diverter.
Sorry to be long winded, but to summarize, getting your boat to ride right is a big part of achieving your speed goals. Not all of it has to cost money. Take a look at your weight distribution and think about what can be done to help that. You have what you have to work with, it is just time to start optimizing your configuration.
Cheers,
Joe
Flusher, mean no disrespect to you at all. But...
Going to have to disagree with the point of moving the weight forward. It is actually the polar opposite if looking for top speed as a number.
The idea is to try to get the hull to "fly". Any weight forward of the center of gravity is hurting you in some form.
I would recommend the weight be transferred rearward and losing unnecessary items from the boat. You would be amazed at what your interior weighs, also moving the weight around can make the boat handle better.
That being said, a back cut shoe will do nothing on a heavy hull unless you have the HP to back it up. I would go neutral cut shoe and a 3*up ride plate, adding a quality loader is a must.
Virtually the only time you see a forward installed motor would be on a hull with a little rocker built into it and very little weight.
Here is a quick list of must have's for your 70 MPH goal.
1. The diet. Get as much weight out of the boat as possible, this may even require drinking light beer instead of the leaded stuff. :-\
Don't forget things like possibly using acrylic sheet for side panels on the upholstery and what not instead of plywood. Also don't forget to check for water logged foam and silly things like that, water weighs 8.33 pounds per gallon, so that adds up fast. One cubic foot of water weighs 62 pounds.
2. Adjustable trim device. A Place Diverter is a must have, used is fine but make sure it is the later flat bottomed nozzle design, it works similar to a ride plate.
3. Keep the weight as centered to the keel as humanly possible. This keeps the hull riding square in the water and reduces the requirement of excessive steering input.
4. Check the bottom for straight, this can be huge if the hull has the typical ride hook built into it. If the hook is present, Grind, block, fill repeat until it is squared up, leave the bottom either really rough or use speed coat to refinish it, a glossy bottom is NOT fast. We were known for taking 40 grit block paper and scouring the ride areas of the race boat.
5. The engine needs to be tough, I don't think there is any engine application more brutal than a jet. Roller camshaft is near a must, which is why I bumped your budget, spend the $1000+/- on a quality roller cam kit. You mention your cam is flat... A roller will simply not ever do that. It's broken, make it better.
6. The tune, I don't care how much horsepower they dyno says you made, unless it is all working together, you will miss your target and get frustrated. You may find yourself playing with different impeller cuts until you get your HP where you need it. Once together, check everything, throttle blade operation, timing curve (I do not recommend going full lock out on a family deal, set it up for 15 degrees advance with it all in by about 2000 RPM. Big carburetor, free flowing exhaust, proper intake, etc...
7. Safety equipment. This should be number one, but have a good jacket and keep your head when making runs.
Good luck, looking forward to seeing your progress...
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Flusher, mean no disrespect to you at all. But...
Going to have to disagree with the point of moving the weight forward. It is actually the polar opposite if looking for top speed as a number.
The idea is to try to get the hull to "fly". Any weight forward of the center of gravity is hurting you in some form.
I would recommend the weight be transferred rearward and losing unnecessary items from the boat. You would be amazed at what your interior weighs, also moving the weight around can make the boat handle better.
That being said, a back cut shoe will do nothing on a heavy hull unless you have the HP to back it up. I would go neutral cut shoe and a 3*up ride plate, adding a quality loader is a must.
Virtually the only time you see a forward installed motor would be on a hull with a little rocker built into it and very little weight.
Here is a quick list of must have's for your 70 MPH goal.
1. The diet. Get as much weight out of the boat as possible, this may even require drinking light beer instead of the leaded stuff. :-\
Don't forget things like possibly using acrylic sheet for side panels on the upholstery and what not instead of plywood. Also don't forget to check for water logged foam and silly things like that, water weighs 8.33 pounds per gallon, so that adds up fast. One cubic foot of water weighs 62 pounds.
2. Adjustable trim device. A Place Diverter is a must have, used is fine but make sure it is the later flat bottomed nozzle design, it works similar to a ride plate.
3. Keep the weight as centered to the keel as humanly possible. This keeps the hull riding square in the water and reduces the requirement of excessive steering input.
4. Check the bottom for straight, this can be huge if the hull has the typical ride hook built into it. If the hook is present, Grind, block, fill repeat until it is squared up, leave the bottom either really rough or use speed coat to refinish it, a glossy bottom is NOT fast. We were known for taking 40 grit block paper and scouring the ride areas of the race boat.
5. The engine needs to be tough, I don't think there is any engine application more brutal than a jet. Roller camshaft is near a must, which is why I bumped your budget, spend the $1000+/- on a quality roller cam kit. You mention your cam is flat... A roller will simply not ever do that. It's broken, make it better.
6. The tune, I don't care how much horsepower they dyno says you made, unless it is all working together, you will miss your target and get frustrated. You may find yourself playing with different impeller cuts until you get your HP where you need it. Once together, check everything, throttle blade operation, timing curve (I do not recommend going full lock out on a family deal, set it up for 15 degrees advance with it all in by about 2000 RPM. Big carburetor, free flowing exhaust, proper intake, etc...
7. Safety equipment. This should be number one, but have a good jacket and keep your head when making runs.
Good luck, looking forward to seeing your progress...
GT Jets,
No disrespect to you brother man. I don’t see the disagreement. And I do look forward to hanging with you in the future.
Maybe I wasn’t clear in my previous post. In my 3rd paragraph, I said, “Moving the weight ahead of the center of gravity will cause the bow to plow through the water increasing drag.” “Any weight forward of the center of gravity is hurting you in some form” was my intent here. Anyway, another opportunity to improve my writing skills.
Good point on putting everything on a diet and removing unnecessary weight. I missed that one in my post, however the intent was there. There will come a point when the OP needs to make a compromise between performance and functionality. Does he want to go fast or enjoy his tunes? Does he want to race or have his friends and family ride along? The more weight he removes, the more expensive weight will cost to remove. It is all a compromise, but as we have both stated, “...moving the weight around can make the boat handle better.”
Regarding the back-cut shoe, it is our current belief that it is not actually the back-cut of the shoe that creates the lift, but the ride plate height. The back-cut surface is simply a necessary transition between the biting edge and the ride plate. Realistically, we are only talking about a surface that is about 2 inches (plus or minus) long (at the biting edge) by 6.415 inches wide.
My suggestions are start with the easy modifications then, move to the increasingly difficult and challenging.
Cheers,
Joe
P.S. I like #3 on your quick list for 70 MPH.
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Excellent read guys!
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GT Jets,
No disrespect to you brother man. I don’t see the disagreement. And I do look forward to hanging with you in the future.
Maybe I wasn’t clear in my previous post. In my 3rd paragraph, I said, “Moving the weight ahead of the center of gravity will cause the bow to plow through the water increasing drag.” “Any weight forward of the center of gravity is hurting you in some form” was my intent here. Anyway, another opportunity to improve my writing skills.
Good point on putting everything on a diet and removing unnecessary weight. I missed that one in my post, however the intent was there. There will come a point when the OP needs to make a compromise between performance and functionality. Does he want to go fast or enjoy his tunes? Does he want to race or have his friends and family ride along? The more weight he removes, the more expensive weight will cost to remove. It is all a compromise, but as we have both stated, “...moving the weight around can make the boat handle better.”
Regarding the back-cut shoe, it is our current belief that it is not actually the back-cut of the shoe that creates the lift, but the ride plate height. The back-cut surface is simply a necessary transition between the biting edge and the ride plate. Realistically, we are only talking about a surface that is about 2 inches (plus or minus) long (at the biting edge) by 6.415 inches wide.
My suggestions are start with the easy modifications then, move to the increasingly difficult and challenging.
Cheers,
Joe
P.S. I like #3 on your quick list for 70 MPH.
You are right, I think it was just semantics.
I am pretty sure we are on the same book, even the same page. My reasoning for the neutral shoe is adjustability down the road. (pretty sure he is going to want too much of both) both being comfort and speed... The neutral shoe is something I feel can be adjusted later, if you start back cut, it is difficult to go back the other way unless you buy more parts. Similar to why I always start guys off with an A or a double A impeller, you cant cut them to be bigger... ;)
I enjoy reading your posts my man. :thumbup:
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So with $3,500 to put in the engine what combo do you guys think I should go with?
And now back to our regularly scheduled topic:
What is reusable from your last engine? You said the cam went flat; did that trash the crank, block, pistons, etc.? Do your rods have the 3/8 bolts or 7/16 bolts? If you have the 7/16, you can put some decent worry free power to them. I think people way underestimate what stock parts can handle. If you are on a budget, no point in spending money just for overkill on something you are not stressing anyway. It depends on how hard you are going to kick it in the guts. It would suck to have rod break and take out a really nice expensive head.
I wouldn’t recommend a longer rod in your application. Longer rods will reduce friction by reducing piston skirt to cylinder wall loads, but might increase the tendency to detonate because of increased dwell time at TDC. A shorter (stock length) rod will favor your lower flowing heads by dwelling at BDC longer, allowing more cylinder filling. Shorter rods also dwell at TDC less (not much) compared to a longer rod, possibly reducing tendency for detonation.
According to Chevy High Performance: Cylinder-Head Flow-Bench Database, the GM 049 iron oval port heads flow:
Lift Intake Exhaust E/I
.050 37 24 64.9%
.100 59 52 88.1%
.200 124 98 79.0%
.300 188 128 68.1%
.400 232 152 65.5%
.500 250 177 70.8%
.600 264 187 70.8%
.700 264 192 72.2%
.800 265 192 72.5%
Avg. 206 147 71.4%
Note: 2.06/1.72-inch valves, 122cc chamber, 253cc intake port. Exhaust flow numbers are with pipe installed. CHP recommends installing the larger valves if horsepower is your goal.
I am now thinking of recanting my former statement and recommending upgrading to the larger 2.19/1.88 valves along with a good 5-angle valve job. I would leave port work for an off-season upgrade, with the exception of slightly blending the transition between the as-cast port and the machined surface of the valve job. Get it together and see how it runs, then contemplate the costs/benefits of port work vs. aftermarket cylinder heads. Realistically, I think you would only gain about 40CFM max (if that) with extensive porting. That would get the flow in the realm of 990 or 188 castings but could make better power because of more quality airflow through a smaller port (increased velocity). My opinion here is that if you have to do extensive porting to meet your performance goals, you have the wrong head to start with.
Looking at the flow numbers, the intake port flow stalls at .600 lift and the exhaust port flow stalls at .700 lift. Opening the valves beyond the stall point of the port does not yield any additional flow, however the valve is held open at peak flow for a longer duration. The Exhaust to Intake Flow Ratio is a little weak (<75%). A low E/I ratio is indicative of a weak exhaust port and not of a strong intake port. Choosing a cam with a split pattern will help the head flow characteristics which is not being helped by the large diameter of your header primary tube diameter.
Cam, Carb, and Compression:
Camshafts
The cam that I would select is most likely going to be controversial to what others would suggest for your application. It is my belief that if you are not taking full advantage of your cylinder head’s flow potential, you are leaving horsepower on the table. However, as was stated earlier, you need to get your engine to produce good power in an RPM range where it will be usable in your application. If you can at all manage it in your budget, I would strongly recommend a hydraulic roller cam/lifters. My choice for cam would include as aggressive a tappet acceleration rate as possible, to provide maximum torque. You will also need good valve springs.
The intake lobe @ .050 lobe lift duration should be in the 218 to 224 degrees range. That should produce a peak power in the high 4000RPM to low 5000RPM range. Here are some intake lobe examples from the CompCams catalog:
Extreme Energy Lobe #3192, 276* Advertised Duration @ .006 tappet lift, 224* Duration @ .050, .378 Lobe Lift, .643 Theoretical Lift w/1.7 Ratio Rocker @ “0” Lash.
XFI Intake Lobe #3014, 268* Advertised Duration @ .006 tappet lift, 218* Duration @ .050, .356 Lobe Lift, .605 Theoretical Lift w/1.7 Ratio Rocker @ “0” Lash.
XFI Intake Lobe #3015, 274* Advertised Duration @ .006 tappet lift, 224* Duration @ .050, .358 Lobe Lift, .609 Theoretical Lift w/1.7 Ratio Rocker @ “0” Lash.
Again, some exhaust lobe examples from the CompCams catalog:
Extreme Energy Lobe #3194, 282* Advertised Duration @ .006 tappet lift, 230* Duration @ .050, .389 Lobe Lift, .661 Theoretical Lift w/1.7 Ratio Rocker @ “0” Lash.
XFI Exhaust Lobe #3036, 282* Advertised Duration @ .006 tappet lift, 230* Duration @ .050, .355 Lobe Lift, .604 Theoretical Lift w/1.7 Ratio Rocker @ “0” Lash.
You can gain a little lift by going to a 1.8 ratio rocker. Be advised that the geometry of the rocker will dictate where the added lift is applied to the valve. Some high-ratio rockers will apply the increased ratio at peak lift while reducing low-lift. Some will increase low tappet lift numbers at the valve, increasing your @ .050 duration (not advertised duration) and will make your engine perform like it has a bigger cam installed. Please see http://www.socaljetboats.com/engine-mechanical-electrical/1-7-vs-1-8/msg223042/#msg223042 (http://www.socaljetboats.com/engine-mechanical-electrical/1-7-vs-1-8/msg223042/#msg223042) for additional info on rocker ratio.
Ready for more controversy? I like tight centerlines, and have run cams in the 106* to 108* in just about everything I have done. More overlap, by decreasing the lobe centerlines, is necessary for top end horsepower. It has been stated many times that large overlap numbers are not “wet” exhaust friendly. This is another compromise that you will need to make. Can you live with running “dry” exhaust (not recommended in your family boat)? OR! Can you handle, as a captain, operating a valve to shut off the water to the headers at low RPM? You can also shim the spring in the Bassett T-valve to increase its cracking pressure, as a secondary failsafe, but you may hurt your engine getting that right. My new thinking on wet exhaust is to run .028 MAX ID jets in the headers with as short a run of hose as possible between the Bassett T-valve and the header water lines so that the pressure in the line drops faster, but that is a whole different topic.
Tight centerlines increase power output, but vacuum at idle and cruise is decreased along with fuel economy. Wide centerlines, 112* to 114* will improve idle quality, increase vacuum at idle and cruise, and decreases fuel consumption. Wide centerlines, and therefore less overlap, will also prevent reversion as the intake and exhaust valves are open at the same time for a shorter period of time as well as at lower lift levels. Basically, wide centerlines will be more jet boat and user friendly. Again, if it was me, I would have the cam ground on a 108* centerline and advance the cam 2* to an intake lope centerline of 106* to start. Also invest in a good true roller timing chain that will easily allow you to adjust cam timing. A gear drive or belt drive will eat away at your budget and can be added later if you like. I like gear drives personally because, if set up properly, will provide rock steady timing that will never changed like a chain or a belt. With that being said, you will be shocked at how much your chain will stretch after just a few hours. You might even consider advancing your cam one more degree to 105* to compensate for that stretch as the cam timing will retard as the chain stretches.
Carbs
What carb and intake do you currently have? Since you are limiting your RPM to the low 5000 range, I would consider an Edelbrock RPM AirGap to maximize torque and economy throughout your RPM range. However, if you wanted to maximize your top end horsepower to reach your speed goals, a good MODERN single plane would be your best choice. If you want to go to the expense and complexity of a tunnel ram, that can be made to work well and give you the associated cool factor. Just keep in mind that you might only be touching the affective operating RPM range of a modern single plane, which could hurt your cruising speed economy and not really help you on the top end. My thinking on carbs has always been to have “just enough” carb for the application to increase midrange drivability. The new school of thought is “BIGGER IS BETTER” when it comes to drag racing and jet boats. It seems that I have been reading recommendations of minimum 850CFM and even square bore carbs pushing 1000CFM. Yet others claim going to a Dominator will give your more horsepower at the same CFM rating. Not too long ago, the carb companies were claiming better drivability and more torque from the big square bore carbs.
As for me, I am a mechanical injection kind of guy. I think going back to carbs would be a step backwards for me.
Young Padawan, ready you are not that step to take. Learn you must, together your engine to keep, before that step you take.
Compression
I would for your compression ratio to be 10.5:1 with your iron heads. Advertised compression ratios never come out where you expect so make sure you measure everything. I would make every effort to get your quench distance down in the .040 to .045 range by zero-decking your block. A tight quench distance will increase burn efficiency, power output, and resistance to detonation.
Another word of caution. When you upgrade to aftermarket heads, your compression ratio with your iron heads will crash big time when you install aluminum aftermarket heads. 1.) The combustion chamber sizes of aftermarket heads all seem to be larger than 122cc. 2.) Aluminum will conduct more heat away from the combustion chamber, reducing burn efficiency. The general rule of thumb when switching to aluminum heads is that you run one more point of compression or one more pound of boost to compensate. Aftermarket heads are not exactly a bolt-on upgrade that you can just slap on in an afternoon and get more horsepower. That too should also be planned. Not all head manufactures offer this, but Brodix offers angle machining (not angle milling) of their heads at time of order to produce rather small combustion chambers. This will allow you to get the compression ratio back up to where it needs to be without decking a huge amount off of your new (expensive) heads.
After spending all this time writing and examining these numbers, I think that it is possible to get to the 500HP mark. 550HP is definitely unrealistic until you start getting into head work and even then, without spinning the RPM up, you are not going to make a lot more than 500 (best case). I would now start considering adding a nitrous kit. Even with stock internals, your engine should handle a small fogger system. Just remember nitrous is addictive and you WILL find the limit the weakest link in your engine.
That centrifugal blower is looking better and better all the time. Building an NA motor is like driving around with half of your plug wires off. Maybe it is just me, but I would put my whole budget into having CSU convert my carburetor into a blow through, a boost retard ignition, and a Procharger (or Vortech); then bolt it onto a sound stocker, and have some fun learning your entire boat. Then build the engine that you want and crank up the boost as budget permits. That is until you reach the limits of your hull.
I hope that this helps.
Cheers,
Joe
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Jeez.... I was just going to say calculate your parts to get the 10:1 compression, bore the cylinders as small as possible to retain bore strength/integrity, go forged pistons on stock length rods with good bolts, forged crank and roller cam...
Now I feel like I am on stage naked and it's cold outside.... :screwy:
Good stuff Flusher, But will add, to utilize a more common single pattern cam you can play with rocker ratios and dumb down the intake to salvage some of the top end torque and provide the ability to have the adjust-ability if the heads get upgraded when he wins the lottery. :sly:
Playin' through... 8)
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Thanks for the detailed replies! I am going to reuse the rods, crank and heads from my engine. Not sure what bolt size the rods are. I already have an eddy air gap on it and a 750 holley but I am going to get an 850 dp holley causer my 750 is shot. I'll upgrade the pistons to boost the comp and I'll look into those cams you posted. I'll probably go with a tapper until I can get nice heads and a better cam. I like your idea of slappin the spray on her! I'll probably buy a nos kit some time in the summer as well. A blower sounds nice but I heard they put a lot of stress on the bottom end and mine will basically be stock besides some forged pistons.
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A blower sounds nice but I heard they put a lot of stress on the bottom end and mine will basically be stock besides some forged pistons.
This is an important myth that I would like to dispel. First off, sure you can make anything fail if you kick it in the guts hard enough. If you are running a pump gas program with a reasonable amount of boost, it should be fine.
The major players in stress on your bottom end are centripetal and inertial forces. These forces are four times greater if the RPM is doubled. For the sake of my feeble math skills, assume a force of 100 pounds at 3000 RPM. That force will become 10,000 pounds at 6000 RPM. I will try to get back to piston speed when I have more time later. It is these forces along with the other parasitical forces, such as friction, that exceed the forces generated by the expanding combustion gasses that cause the torque and horsepower curves to drop during dyno testing. And the reason why everybody is afraid to RPM up the engine with internals that are not up to the challenge.
Centripetal force is a force that makes a body follow a curved path (crankshaft, rod bearings, and big end of the rods).
Inertial forces - Inertia is the resistance of any physical object to any change in its state of motion including a change in direction (pistons, pins, rings, and small end of the rods). The mass of the pistons etc. accelerate down the bore as the air/fuel mixture expands. This mass needs to then decelerate at the end of its stroke at BDC, stop, reverse directions, then accelerate back up the bore towards TDC, and repeat. These inertial forces are greatest when the piston changes directions at TDC and BDC. But let’s look at that in greater depth per cycle:
1.) Compression Stroke - the air/fuel mixture is compressed into the combustion chamber by the piston moving up in the cylinder bore, the forces on the rod are in compression.
2.) Combustion Stroke - Air/fuel mixture, expanding as it combusts, pushing on the piston to drive it down. Again, the rod is in compression.
3.) Exhaust Stroke - the exhaust valve opens and the piston changes direction forcing the consumed air/fuel mixture out through the exhaust port. Yet again, the rod is in compression.
4.) Intake Stroke - At TDC, the piston changes direction to move towards BDC while drawing in a new air/fuel mixture through the intake port. The flow of the air/fuel mixture moving through the intake puts resistance on the piston moving down by the means of a reduction in pressure above the piston. There is also frictional resistance, resistance from a differential in pressure from the crank case side of the piston to the combustion chamber side trying to push the piston back up the bore. It is this point where the greatest forces are being exerted on the rods and pistons because the rods are now placed in tension.
In a supercharged application, boost will help to push the piston down, placing less tension force on the rods. The forces on the rods will actually be slightly less during this changeover between the exhaust cycle and the intake cycle. The forces on the pistons and rods during the combustion cycle will not reach the forces that are exerted during this changeover. Not at your power levels anyway, not to say that you wont eventually get there.
Next, we come to the blower drive. YES, this puts a lot of stress on the snout of the crankshaft. Compressing air is doing work and with any crank driven accessory that is doing work, additional forces are being applied to the cranks. So much so that blower engines that are making good boost (or for the above mentioned forces turning the blower) are great enough to shear a single keyway and spin the crank up. Any belt drive is also imparting a great deal of bending force on the crank as well.
The reason why I recommended a centrifugal over a roots or screw is because the centrifugal really isn’t producing significant boost at lower RPM. In a car, the centrifugal has the worst features of both a turbo and belt driven supercharger. The impeller has an RPM window within which it needs to operate to produce boost efficiently. Below that RPM and you are not producing any boost. Above that and the tips of the impeller wheel break the speed of sound which could cause damage to the blower. In a car, because a centrifugal is driven in relationship to the crankshaft, the compressor wheel only gets to its ideal RPM for a split second, then it slows after the gear change and has to come back on its curve. In a jet boat, you simply calculate the drive ratio to match the RPM of the engine and pump. At cruise speeds, hardly any boost will be produced; so, realistically, you will really only be in a boost condition at WOT. Of course there are ways around that if you want to kick it harder, but that is another topic.
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Just say’n... you will make way more PUMP GAS POWER with a supercharger ON THAT ENGINE than you ever will with any cam, heads, and intake combo AND it will live longer.
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I already have an eddy air gap on it and a 750 holley but I am going to get an 850 dp holley causer my 750 is shot.
You might call Dennis and/or Kevin at CSU and inquire about having yours upgraded. Might save you a few bucks over buying new.
http://csucarbs.com/ (http://csucarbs.com/)
I'll look into those cams you posted.
Those are cam lobe profiles selected out of the CompCams Master Lobe Profile Catalog, not actual cams. If you wanted to have a cam custom ground, that is where you would select the profiles. Bullet/UltraDyne Cams has some real aggressive and modern profiles that rocket-ship open the valves and don’t hammer them closed. The only reason I selected from the CC catalog, is that I have it to look through and the last engine I built used the lobe profiles Extreme Energy #3192 intake and Extreme Energy #3194 exhaust ground on a 108* centerline. That engine produced peak power at 5400 RPM and carried it until 5800 RPM (without dropping) when the dyno test ended because the HP numbers were not climbing any higher.
The lobe profiles that I listed are for hydraulic roller lifters. Going with a flat tappet cam, you will not be able to reach the same lift numbers in as short a duration ~220* @ .050. You can always spin the RPM faster and cut down your impeller to match, but in a heavy boat, you won’t want to go too small. Zinc additive will also help an aggressive flat tappet cam live.
I am far from a cam guru, but what I have been reading from those who have posted cam theory, the characteristics of that engine meet most of the requirements of a cam selection for a jet boat. Peak horsepower was at 5400 RPM, in keeping with suggestions by GT Jets and Six-oh-nine, and corresponding to the Jack Seastrum Berkeley Impeller chart for an A impeller. Peak torque was below 3700 RPM (where the dyno test started), but it held a very flat torque curve through the end of the test. That would put your peak torque right around your cruising RPM.