# Reducing compression for turbo use.



## Roop (Sep 5, 2003)

Whats a) the best way of reducing cylinder compression prior to fitting a turbo to a normally aspsirated engine and b) what's the most cost effective way?


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## TheVodKA (Sep 19, 2002)

Best way: Getting lower comp pistons

Most effective way: Thicker Headgasket


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## holy200sx (Jan 8, 2003)

lol, if you get really balsy.. and im talking like.. super god ultra balsy..

get a CNC machene to duplicate the head gasket, and print it out in 1/2" stainless steel, then put a head gasket on top of it, and one on bottom... then you can have one stroker GA.


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## rios (Jun 10, 2002)

holy200sx said:


> *lol, if you get really balsy.. and im talking like.. super god ultra balsy..
> 
> get a CNC machene to duplicate the head gasket, and print it out in 1/2" stainless steel, then put a head gasket on top of it, and one on bottom... then you can have one stroker GA. *


vhat? is this true or is this some sort of farce?


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## holy200sx (Jan 8, 2003)

think about it.. you are making more space inbetween the piston and head.. maybe not 1/2 inch.. but lower comp pistons are simply shorter pistons.. but. its down to a MUCH more presice measure... as far as it being a stroker... lol.. technically speaking.. it would be a bigger combustion chamber.


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## Roop (Sep 5, 2003)

Welll, from a practical point of view two head gaskets would be simple AND cheap but I feel uneasy about the flexible element of a double thickness gasket. Is it more prone to leaking?
I can get metal laser cut. The only snag is finding the right thickness and metal (aliuminium/copper).
And to my next question: what thickness head 'gasket' gives the appropriate compression reduction? And while I'm at it; what is the appropriate compression reduction? Is there some mathematical formula or summin'??


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## chimmike (Oct 17, 2002)

if you have a pulsar, SR20DE, a GTiR Pulsar, you've got 8.3:1 compression, iirc....or is it 8.5:1? Either way, you don't need to be reducing compression for turbo.


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## javierb14 (Jul 9, 2002)

*Tuning is very important*

on the topic of compression ratios and high whp.....my next motor will most likely be a high compression turbo motor 

this is 10:1 b18 with a SC61(big T3/T4). it made 520whp at 25psi...tuned by tony at jotech motorsports. it also did 372whp and 231wtq at 9psi on pump gas, which is 93 octane in Tx. enjoy

right click, save as 

dyno run

running a supra: 
[email protected]=520whp 225/50-15's DR's 
[email protected]=520-540whp 

run 1

run 2

oh ya, its a 10sec street car too


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## Roop (Sep 5, 2003)

so how do you stop pre ignition at those pressure ratios on 'pump gas'. And does'nt it knock the bottom ends out? Do you need to consider a stronger crank if you turbo a factory N/A engine???


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## javierb14 (Jul 9, 2002)

very conservative tune.


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## holy200sx (Jan 8, 2003)

god with those high comps.. do you still use a high rev limiter?... i would think you would keep it low eh?


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