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Discussion Starter · #1 ·
Lowering the Compression on a K20 Motor for a Turbo & general question on engine mods

Hello

I am in the process of building a K20A2 Motor for my RSX Type S. I would like to be able to use pump gas so it can be somewhat of a daily driver. The standard K20A2 motor puts out about 200 HP and 142 Ft Lbs of torque with a 11:1 Compression. Since I would like to install a turbo but still use pump gas, I would like to lower the compression to 8:1. At this compression, how much boost can I use on pump gas (91 octane)? Also when I lower the compression, how do I calculate my HP and Torque? I know it will lower it but I do not know how much. Also how do I calculate the compression ratio (prefer the dynamic) at different PSI of boost? I am looking to do between 15-20 psi. I have found some compression calculators but none are really good for the K series motor. I would like to have around 300 whp but I don't know if this is achievable with a 4 cylinder on pump gas.

I am going to install Brian Crower Stroker Kit to make the engine a 2.35L. The turbo I am planning to use is a Full-Race twin Scroll turbo. I am also planning to redo the head and send the tranny out to gear speed in California to get strengthen for the rebuilt motor.

Any watch outs that I should be aware of with these type of engine mods?

Thanks,
R
 

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Re: Lowering the Compression on a K20 Motor for a Turbo & general question on engine

8.1 cp? jesus thats low. i run 10:1 with 91 and my friend ran 18psi 6766 91octane and 32psi c16.. with 11:1 sleeved k24.
 

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Re: Lowering the Compression on a K20 Motor for a Turbo & general question on engine

That is interesting especially the 11:1 compression ratio. Are you running a secondary unit to help with your a/f ratio? I heard you can run Methanol for this but I don't know too much about it. All of the compression calculators that I have found show if I run too high of a boost my dynamic compression ratio gets too high, which means I have to use higher octane. I picked 8:1 compression ratio because that seems to be the norm for V8s and that's what I am some what familiar with. I would think that 4 cylinders have the same limitations as V8s when it comes to compression ratios and octane, unless there is something I am missing?

Does anybody know a good compression calculator for turbos?
The one that I have used is:
http://www.zealautowerks.com/kseries.html

Thanks,
R
 

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Re: Lowering the Compression on a K20 Motor for a Turbo & general question on engine

That is interesting especially the 11:1 compression ratio. Are you running a secondary unit to help with your a/f ratio? I heard you can run Methanol for this but I don't know too much about it. All of the compression calculators that I have found show if I run too high of a boost my dynamic compression ratio gets too high, which means I have to use higher octane. I picked 8:1 compression ratio because that seems to be the norm for V8s and that's what I am some what familiar with. I would think that 4 cylinders have the same limitations as V8s when it comes to compression ratios and octane, unless there is something I am missing?

Does anybody know a good compression calculator for turbos?
The one that I have used is:
http://www.zealautowerks.com/kseries.html

Thanks,
R
Although you are on the right track.. well.. no not really.. lol you are stuck under a LOT of old information, technology improves so much every year we can do so much more with what we have.. so basically saying you dont need to over complicate your project. there are plenty of proven stock motor turbo setups, that you wouldnt need to touch a thing unless your looking for 500+.

So lets start over.. forget all that 1990 stuff your talking about with 8:1 compression.. you want to make 300whp? geez I wish i had people like you walk thru my doors every day. the most simple setup i would build someone would be bone stock motor (not even head studs) and 6266 will net you 450whp at 15psi. maybe 420ish at 12psi to play it safe with 91.. although we have 93 here.. on e85 and 18-20 psi i would be shooting for 500.

so no need to touch anything. dont invent the wheel for such a simple goal!
 

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Re: Lowering the Compression on a K20 Motor for a Turbo & general question on engine

Don't touch anything. Slap a turbo on it and call it a day.
 

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Discussion Starter · #6 ·
Re: Lowering the Compression on a K20 Motor for a Turbo & general question on engine

I take it that 6266 is a turbo? Is this a particular model I should go after instead of the full-race one? I am not too familiar with turbos so sorry if this is a stupid question.

Another stupid question, what has changed that allows up to run high compression with a turbo? Is it the new turbo models? The computers?
 

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Re: Lowering the Compression on a K20 Motor for a Turbo & general question on engine

I take it that 6266 is a turbo? Is this a particular model I should go after instead of the full-race one? I am not too familiar with turbos so sorry if this is a stupid question.

Another stupid question, what has changed that allows up to run high compression with a turbo? Is it the new turbo models? The computers?
whats the address to that cave you popped out of? :) jk jk

well... there are many turbos out there.. so are more reliable and some make better power.. either way almost any turbo you decide to go with will get you your goal.

precision turbo has great turbos.. 5858 (have one for sale) 6266 & 6466 etc etc which are rated for 600, 700 & 900 hp.

basically tuning technology has come a long way, fuel correction is very precise and since we dont need a huge margin of error we can get away with high compression which actually helps motors spool turbos faster and make better power.. back in the day everything was 8:1 because we didnt have much options with gas and turbos sucked, and everything was designed poorly that such low compression would allow a big area for mistakes, which now a days is very different.
 

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Re: Lowering the Compression on a K20 Motor for a Turbo & general question on engine

I figured it was a turbo, as for what cave I am at, I am not new to building motors or tuning them. In fact, I just did built a LS1 motor and tuned it myself using HP tuner. Maybe I need to do a little more research but I will figure it out. I just don't want to be one of those people that build their motor (or even worse pay someone to that for them) and have it blow up on them. I see too many imports that are built incorrectly. In fact, I have seen one very similar to what I want to build but he is on his third motor and second turbo. When I make something I want it to last or at least make me laugh my @$$ off when it goes.
 
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