SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: rstp on December 25, 2008, 05:48:31 AM
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I have a 1977 19 foot tahiti mini with a stock 454 and would like to know whats a good comp. ratio to run at on pump gas and how much hp if any would you gain just by raising the comp.
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i would think 10-1 with a good tune. raising the c/r wont get very much hp by itself. remember in a jet boat 50hp doesn't mean much because the impeller will absorb it without much speed gain. i think a cam, headers and good carb will give you the best bang for buck. just my x-mas .02
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I have a 1977 19 foot tahiti mini with a stock 454 and would like to know whats a good comp. ratio to run at on pump gas and how much hp if any would you gain just by raising the comp.
A lot of the time a good camshaft and timing set will be the largest seat of the pants gain, if your BBC is truely stock, you may find the cam timing is retarded due to the year, in the late '70's almost all of the Big Three had to retard the cam timing to be able to pass the SMOG mandates, this is actually most noticable on the 460 Ford, I am with Ralph 100%, 10.0:1 is more than enough with pump gas, the cam profile will actually raise cylinder pressures all by itself. Not much to be gained by CR itself, it would require a retarding of the ignition timing to prevent detonation, taking away any gains you would have made, you can get away with much more with a lower CR...
By the way, all gasoline comes from a "pump". ;D ;)
Good Luck!
GT
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GT Jets and Ralph...
I think 10.1 is plenty( w/proper cam/camtiming /tuning.etc.) --for pump fuel :)
In other words I agree 100 % w/ both of you. You already have the c.i.d. ;D
P/S happy holidays!
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As already said, 10.0:1 is good for compression.
But if your considering rebuilding the engine there is a lot of performance gains available in the cylinder heads. Either porting the original heads or up grading to a set of performance aluminum heads will help.
Some of the other things to consider are intake manifold, carburetor(s) and a good ignition system.
What are you starting with and what do you want to do when completed?