SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: tmorgan on November 22, 2015, 09:35:06 PM
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So I'm looking to pick some brains here I have a 77 eliminator bubble deck and since she's down for the winter I am thinking of doing some engine work to her I would like to run pump gas and keep it reliable. preferably keep it n/a but want to get some more out of this old 460. I'm not quite sure what hp numbers this hull is capable of handling which is limiting my ideas. right now I'm guessing she's sitting around 450 hp running some worked over d3 heads mild cam edelbrock intake and some other little adjustments. I know these heads need to go to get some real numbers out of it and maybe punch out the cylinders a little bit. I'm trying to get to the 600 hp mark or so. What do you guys think?
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Good flowing heads, with an appropriately small port volume to keep flow velocity high, is essential along with a good intake. Get your static compression ratio in the 10.5-11:1 (w/aluminum heads) range. You are going to need a roller cam pushing .700 valve lift.
If it is in the budget, consider a stroker. At 466CI, your 650 horsepower goal works out to be 1.39 horsepower per cubic inch. At 514CI (4.25 stroke), that works out to be 1.26 HP/CI. More cubic inches could allow you to run slightly less compression ratio for your fuel selection.
P.S. Don't dismiss a centrifugal supercharger
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Thanks for the input flusher. I'd love to have a supercharger but of course who wouldn't haha I'll have to look into the centrifugal supercharger cost compared to an old screw type. Sure would be nice to throw an 871 on it with some engine work and call it a day but the budget won't allow all that at least this winter. Also a few people advised not to run aluminum heads on these river boats due to erosion from sand and what not in the water and to keep iron what's your thoughts on that?
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Thanks for the input flusher. I'd love to have a supercharger but of course who wouldn't haha I'll have to look into the centrifugal supercharger cost compared to an old screw type. Sure would be nice to throw an 871 on it with some engine work and call it a day but the budget won't allow all that at least this winter. Also a few people advised not to run aluminum heads on these river boats due to erosion from sand and what not in the water and to keep iron what's your thoughts on that?
Aluminum heads transfer more heat from the combustion chamber and reduce hot spots, reducing potential for detonation. General rule of thumb, aluminum heads require one more point of compression or one pound of boost to bring the combustion temperature back to that of cast iron heads. Actually, everything being equal, cast iron heads will make more power because of heat retention. The problem is availability of performance cast iron heads.
An advantage of aluminum is the weight savings over iron not to mention repairability of aluminum.
I think that contact with water is much less than that in a car with a closed cooling system, however marine application heads are available hard anodized.
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Once you go forced induction, the need for good flowing heads becomes less important as does a big cam. The supercharger easily overcomes the flow deficiencies of stock or entry level heads.
I would put my money into a good rotating assembly and an efficient supercharger. Personally, I am a roots guy, so I get it, if that is what you want. As a car guy, centrifugal superchargers have the worst features of both a belt-driven supercharger and a turbo. Once the centrifugal reaches its peak RPM, it's time to shift. A jet boat doesn't have that issue. The engine, the pump, and the centrifugal supercharger are all operating at their intended RPM.
Just food for thought,
Cheers,
Joe
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I run a 557 ci ford with 429 heads, ran it great motor. The boat had issuers took it all apart last year. Have a Taylor boat and haven't started my new project yet still building my yellow hydro 498 roller motor almost done,
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I am running trw piston eagle rods Brodix heads forged crank bored 0.30
708 sold roller cam crane gold roller rocker super victor intake and 1050 dominator according to the shop that is working on the heads I should be making 1.55 hp per cubic inch
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I am running trw piston eagle rods Brodix heads forged crank bored 0.30
708 sold roller cam crane gold roller rocker super victor intake and 1050 dominator according to the shop that is working on the heads I should be making 1.55 hp per cubic inch
Assuming you are running a 4.280 (+.030) bore 454 and not a 4.550 bore, those numbers are right on par with my speculation. A while back I read that in a conventional head BBC, .100" valve lift is required for every 100 horsepower. That also assumes decent flowing aftermarket heads running around 11:1 compression.
Looking at various combinations and dyno sheets, as well as actual real world performance, that seems to hold true.
However, to the best of my knowledge, dyno testing was NOT performed with pump gas in any of these instances.
That being said, power numbers will be down running pump gas and more so if timing needs to be pulled to prevent detonation.
My thinking is that a more efficient head is required to compensate for limitations brought on by the fuel choice. An intake and exhaust that doesn't restrict the flow of the heads (below the following value), but has the appropriate cross-section to maintain good port velocity should be selected. Careful attention to air/fuel mixture motion and quench can pay off big time.
Minimum peak airflow per cylinder @ 28" multiplied by .257 is the theoretical horsepower potential of the heads. Peak airflow is what the engine actually sees. If the heads flow to .800 valve lift but the cam only has a lift of .650, the flow at .650 should be used instead of .800. The exhaust to intake ratio should be in the neighborhood of 75%.
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I am 12 to 1 been down this road already did homework. Already
Pistons have a 38 cc dome
Cam 268
271 @50
Intake 705
Exhaust 708
Heads are milled to 113cc
30 over
Head gasket is 38 thou thick
6.135 rods eagle
Forged crank
Gear drive
Super victor vr intake
1050 dominator
Along with that the shop who is doing the work has said that's what it should be I'll know more when it gets dynoed
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Are you running pump gas? Correct me if I'm wrong but at 12:1 you'll have to run higher octane than what you're getting from the pump
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I will be doing a blend I am running aluminum Brodix heads
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Correct me if I'm wrong but at 12:1 you'll have to run higher octane than what you're getting from the pump
There are three different compression ratios in an engine:
1. Static compression
2. Dynamic compression
3. Effective compression
Static compression is the actual measured volumes.
Dynamic compression is loosly based on static compression, but uses the closing point of the intake valve as the stroke to calculate the volume above the piston. This is a function of the stroke, rod length, and the degrees after Bottom Dead Center (BDC) that the intake valve closes. This is because air can not be compressed until it is confirmed. Basically, a larger cam requires more static compression to produce the same cylinder pressure.
Effective compression is what the engine actually experiences while running. It is a product of dynamic compression ratio and volumetric efficiency (VE). Good flowing intake and exhaust systems promote higher VE, restrictive ports or overly large (lazy) ports with low velocity can reduce VE, as ca the operating environment.
Check out these other threads for additional information:
Another cam question bbc
http://www.socaljetboats.com/index.php?topic=23935.msg278726.msg#278726
How to choose the right octane?
http://www.socaljetboats.com/index.php?topic=23425.msg271550.msg#271550
VE changes throughout the RPM range with peak VE being at peak torque RPM. For every VE, the dynamic compression will compress the air/fuel mixture X amount with a corresponding increase in temperature. This change in temperature is added to the Intake Air Temperature (IAT). Heat is always conducted from areas of high temperature to areas of low temperature. Combustion chamber heat can be lost or gained by conduction through the cylinder walls, piston domes, combustion chambers in the heads, valves, head gaskets, or any surface that is in contact with the air/fuel mixture that I might have forgotten. In the event of supercharging, the turbo or blower heat the air in its own right in which case, this number is added to the sum above. If this number is greater than the flash point of the fuel, prior to ignition, detonation will occur.
Then there is the matter of mixture motion inside the combustion chamber. A highly turbulent mixture is homogenous and burns evenly. Fuel droplets fall out of suspension and/or from large droplets that do not burn evenly.
Here is a good article by Jim McFarland on burn patterns:
http://www.hotrod.com/how-to/engine/ctrp-1108-combustion-patterns/
A good article on compression ratio by Da Viz:
http://www.hotrod.com/events/coverage/0311em-power-squeeze/
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Thanks for the info some good stuff here for sure!
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