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Compression Calculations

This is a discussion on Compression Calculations within the Internal Engine forums, part of the LSx Technical Help Section category; Does anyone have a formula to calculate static compression ratios for assembled engines? I figure X= bottom end compression and ...

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    GM made me do it!! IT_SS's Avatar
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    Compression Calculations

    Does anyone have a formula to calculate static compression ratios for assembled engines? I figure X= bottom end compression and Y= top end compression, so X + Y = Total static compression????? or is it X(Y)/2?

    I'm asking because in the next year or so I'll be starting my FI build, and I'm in the planning phase now and I want to make sure my numbers are right. The Lunati 395 Stroker Kit seems to be the direction I'm going in. The kit is offered in 3 different compressions :

    8.7:1
    10.4:1
    12.2:1

    In my mind, the 10.4:1 would be the wiser choice to use with say and LS head with these specs:

    Combustion Chamber: 72cc
    Intake Runner: 227cc
    Exhaust Runner: 70cc
    Intake Valve: 2.055"
    Exhaust Valve: 1.57"
    (Patriot Performance LQ9 Stage II)

    Which advertise a drop from 10.1:1 to 9.0:1 on a stock LS1. So if X(Y)= Z, am I looking at a 9.5:1 compression?

    I've also posted this on LS1Tech
    Last edited by IT_SS; 03-23-2009 at 09:16 PM.
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    King 0f n00bz shady milkman's Avatar
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    its much more complicated..you need to know Bore,Stroke,Head Gasket Thickness,Deck Height,Piston Dome cc..like (-2 etc) ,Combustion Chamber of the heads

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    blacker than wesleysnipes
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    plus i doubt that stroker that is pushing the limits as is for a ls1..will be able to handle boost etc...why not go 402-08 or just do a 346ci with forged internals and boost the fuck out of it..

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    Quote Originally Posted by shady milkman View Post
    its much more complicated..you need to know Bore,Stroke,Head Gasket Thickness,Deck Height,Piston Dome cc..like (-2 etc) ,Combustion Chamber of the heads
    Quote Originally Posted by shady milkman View Post
    plus i doubt that stroker that is pushing the limits as is for a ls1..will be able to handle boost etc...why not go 402-08 or just do a 346ci with forged internals and boost the fuck out of it..
    I figured it would be, I'm looking @ the 395-6 CI forged internals because of the price, but if i keep the stock crank, i would just have to worry forged everything else.....hmmm

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    blacker than wesleysnipes
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    why not get a forged crank ? ..dont go half ass and cut corners when it comes to strokers or forging when going the FI route..YOU WILL BE SORRY~! and it will be expensive

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    Quote Originally Posted by shady milkman View Post
    why not get a forged crank ? ..dont go half ass and cut corners when it comes to strokers or forging when going the FI route..YOU WILL BE SORRY~! and it will be expensive
    well, getting the forged crank justifies the 396 stroker, that's as high as an LS1 can go with out re-sleeving the block to my understanding. Im my mind, the goal is a 396 stroker twin turbo, no matter what tho, forged internals are a must!!!

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    blacker than wesleysnipes
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    Quote Originally Posted by IT_SS View Post
    well, getting the forged crank justifies the 396 stroker, that's as high as an LS1 can go with out re-sleeving the block to my understanding. Im my mind, the goal is a 396 stroker twin turbo, no matter what tho, forged internals are a must!!!
    nice but pushing the limits of the already thinned walled ls1 then pushing pushing boost on top of it isnt the best idea..why not a 383 TT project..i think you will be much happier with that set up ..since you will have a little leeway for things

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    Quote Originally Posted by shady milkman View Post
    nice but pushing the limits of the already thinned walled ls1 then pushing pushing boost on top of it isnt the best idea..why not a 383 TT project..i think you will be much happier with that set up ..since you will have a little leeway for things
    that has a bit of a sexy ring to it...383 twin turbo..... I just want to make sure i can hit 9.0:1-9.5:1....

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    Quote Originally Posted by IT_SS View Post
    that has a bit of a sexy ring to it...383 twin turbo..... I just want to make sure i can hit 9.0:1-9.5:1....
    well you can always pick up a cheap lq4 and you will have nooo prob getting that ratio..just make sure you get a short/long block that is made for FI..for example the ls3 427 from texas speed is not made for fi at all..but the heads and cam make or break that set up

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    Quote Originally Posted by shady milkman View Post
    well you can always pick up a cheap lq4 and you will have nooo prob getting that ratio..just make sure you get a short/long block that is made for FI..for example the ls3 427 from texas speed is not made for fi at all..but the heads and cam make or break that set up
    im either going to get the patriot performance LQ9 stage II or port a set of LS1 heads i have @ home......

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    Quote Originally Posted by IT_SS View Post
    im either going to get the patriot performance LQ9 stage II or port a set of LS1 heads i have @ home......
    go big or go home..if your aiming for a TT dont take a shortcut on the heads..

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    patriot performance LQ9 stage II it is, now to start selling drugs....

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