Compression ration for 14lb boost
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Staging Lane
Joined: Feb 2005
Posts: 73
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Compression ration for 14lb boost There are not too many off the shelf options for 402 pistons. One option is a Diamond -14cc which will give about 9.5:1 with a 72 cc head. Another is a Mahle -32cc which will give about 8.85:1 (I think). I'd like to run 91 octane at 8lbs and 2 cans of torco + 91 octane at 14 lbs. If I have to I will run a mix of 109/91 in the ratio of 30/70. What would be a better way to go? Is 9.5:1 too high. What is the optimum CR?
Application:402 TT
Application:402 TT
depends on how much boost you plan on running.
id say most popular setup on big Cube motors tend to be in between 8.0 and 8.7 or so, most usually at 8.5 Reason for that I believe is because you can have lower compression motors to run more boost and be safer because the cubes will still get you the tq you need to get moving at lower rpms...
id say most popular setup on big Cube motors tend to be in between 8.0 and 8.7 or so, most usually at 8.5 Reason for that I believe is because you can have lower compression motors to run more boost and be safer because the cubes will still get you the tq you need to get moving at lower rpms...
Also depends on whether or not you run an intercooler, what your FI efficiency is, whether you can inject extra fuel to cool the mixture, etc. There is no cut and dry formula for CR.
My 383 is about 9.5:1, and I am running a monster air-to-air intercooler after the Vortech. I am still tuning but am getting about 8lbs. of boost at 6200rpm. No knock yet.
Jim
My 383 is about 9.5:1, and I am running a monster air-to-air intercooler after the Vortech. I am still tuning but am getting about 8lbs. of boost at 6200rpm. No knock yet.
Jim
Launching!
Joined: Dec 2001
Posts: 289
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From: Wallingford, CT
If this is for a street car, I'd mimic the OEM offerings. Low compresion in the 8.0 -8.5:1 neighborhood.
If you are defining the specs on a new engine, get the compression down as much as possible.
For a street car, you want to run 93 octane with full timing. Why neccessitate race gas when you can just up the boost a little?
Anyway, thats me. I'm just getting my engine rebuilt at 8.25:1. I consider that to perfect.
If you are defining the specs on a new engine, get the compression down as much as possible.
For a street car, you want to run 93 octane with full timing. Why neccessitate race gas when you can just up the boost a little?
Anyway, thats me. I'm just getting my engine rebuilt at 8.25:1. I consider that to perfect.
run the 8:85:1 keep your timing conservative and you should be able to do it. A little octane booster just to ensure no detonation. As long as your fuel system is up to snuff you should be able to do it. Just run it a little rich.
