SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: propless on July 09, 2010, 10:44:14 PM
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OK engine gurus, I have a question.
Lets say someone ::) wanted to put together a high compression BBC. Lets say this someone wanted around 12:1 compression (or a bit more). Is there a point where the piston domes become a real issue with flame travel ? Most of the heads this someone is seeing are up around 119/120cc, so a fairly large dome would be needed. The engine in question will be .030 over 454 with 4.25 stroke (thats the plan so far).
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proppy..
From my uncle, the guru of the machining world..
Get the heat as deep into the cylinder as you can for RPM, and as high in the cylinder for torque no matter what the CR...
That being said, the shape of the dome in relation to the combustion chamber is more important than all else. The confusing part comes when talking about RPM and and quench area...
Look into some later Vortec heads, I have heard that they work pretty well in high compression applications, but are not very tough.
The type of intake and exhaust will greatly effect these also, flame travel is based totally on air charge velocity and piston speed........
GT
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Sorry, but late model Vortecs aint gunna cut it GT. This someone has been lookin at the AFRs and such. Need lots of exhaust flow.
Intake is an 871 / injected, exhaust is zoomies, and fuel is not gas. :-X
This someone has been going round and round with the idea of low comp/high boost vs high comp/low boost. This someone likes the idea of high comp/low boost.
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Sorry, but late model Vortecs aint gunna cut it GT. Been lookin at the AFRs and such. Need lots of exhaust flow.
Intake is an 871 / injected, exhaust is zoomies, and fuel is not gas. :-X
Well, that changes everything..BTW, it is commonly called "flame front travel" ;)
Of the two force fed engines I have ever gotten to play with, I will say get the smallest chambers possible and the flattest smoothest pistons made....It will pay dividends in the end when it comes to turn key reliability...Domes are the weak link when it come to the heat of compression, inter cooler is all I will add...The Zoomies will indeed keep things moving... :thumbup:
You need to talk to Gromm Racing Heads.....These guys are the Shizzle and well known. (408) 287-1301 They are in San Jose.
GT
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I run blower pistons, prolly 8:1 and a 10% over 6-71. Should run 9 psi @ 6000 RPMs. I feel this is a very mild setup. Good for cruising and I hardley EVER get into the secondaries, two 1050's. Heads are 990's. What fuel are we talkin? alky, E-85?
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HD, its going to be an E85 only motor, no switching back to pump gas. Ive seen guys say there running 9:1 and 22+lbs boost on the stuff, As well as a turbo deal thats 8.5:1 with over 30lbs so It should be fine with the cylinder pressures. I dont think the blower in question will make those kind of crazy boost numbers. Thats the reason for the high comp/lower boost idea.
GT, I was thinking the same thing, small chamber and flat tops (or close to it). And if it was a Ford that would be no problem, lots of small chamber heads for those (down into the mid 70cc range). But I cant find any good aftermarkets like that for a Chevy. Theres got to be a way around the big dome piston deal. Those things are lumpy, bumpy and heavy.