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Turbos and compression

James

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A friend of mine starting to gather Intel and source parts to turbo his CRX that has a 2000civic SI motor swapped in.

This was all fine and dandy until today he tells me the previous owner claimed to have swapped in high compression pistons and it conpression tested at 250-260 per cylinder.

That's way to high for a turbo setup isn't it? I've never really delt with anything other than stock conpression Dsm setups so fill me in!
 

LIV4PSI

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Isn't cylinder compression different than piston compression? I don't know much, but that sound too high for boost, especially on pump gas. E85 would help, or maybe install a thicker headgasket?

I'm way out of my league here, I probably shouldn't have posted. /ubbthreads/images/graemlins/dunno.gif
 

James

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I appreciate any input, if you're not positive just say so ( as you did). So now other people that actually have the answers can agree with or correct it.
 

LIV4PSI

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I know piston compression and cylinder compression are different, as the names imply. I do not know how much one affects the other, as in how much a higher CR piston will raise the engine compression.

E85 helps with higher compression, no doubt there. I know a thicker head gasket will help lower the compression, but I don't know if it will help enough.

I always mention it when I'm not sure. Hopefully I can help you out a little, and learn a little in the process. Or at least that was my goal.
 
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James

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I know he won't be doing E85 in his CRX, he only wants to run minimal boost an this is first ever project... Also it's his DD lol.

He's basically trying to bolt on, tune, and go.

He's planning on using 14b turbo and 1g BOV :p
 

James

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Nobody has anything to add?
 

quato

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I'll throw this out...

Back when I had an S2000 (11:1 comp), I was looking a putting a turbo on it and about the max boost people were looking to "safely" get was around 7psi intercooled. I *think* the comptech s/c does around that with water/air.
 

LIV4PSI

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I did some google searching. The average cylinder compression is 180-190, so your friends it abnormally high. The stock piston CR is 10.5:1, which is dangerous for boost already, as its higher even for NA. Running under 5lbs of boost on a 14b turbo isn't really worth the effort IMO. And I would never turn my only car into a project car.

It sounds like your friend is cheap and wants a reliable turbo build. You know the saying: Cheap, fast, and reliable, Pick which two you want.
 
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James

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He's not being cheap, he has $2000 to spend on his build. He wants the 14b because he likes the feel of it in my car, and it's cost effective, good for low end boost, and with some customizing can be used for higher boost.

For the learning process, why is high compression bad for boosted applications? Does it make a difference turbo or supercharged? How can he lower his compression?
 

JNR

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Damn, wish I could add a turbo for only $2K!

forced induction basically adds to the compression ratio and in addition creates heat, so the engine is then much more likely to knock or detonate, go lean, etc....there are ways to combat most of that (intercooling, more fuel, richer mix, etc.)...the higher your static compression ratio is (think of baseline ratio), the less additional pressure (boost) you can do, as that raises your total effective compression ratio (base/static and additional pressure).

with higher performance cams, aluminum heads and such, you can bleed off some of the pressure, but youreally risk getting too much with higher static CR...we're lucky we have EFI and electronics, but even on a N/A engine, 11.0:1 is pretty high...I wouldn't risk any boost on it, as it would almost be useless (max 5-10 psi, let's say and that's nothing for a puny 4 cylinder).

as a GENERAL rule of thumb: increasing compression ratio 1 point (1.0, not 0.1) = ~4% increase in power.

Here's a handy chart I stole off another website...see how high the compression ratios get!

 
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TomN

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Quoting James:
He's not being cheap, he has $2000 to spend on his build. He wants the 14b because he likes the feel of it in my car, and it's cost effective, good for low end boost, and with some customizing can be used for higher boost.

For the learning process, why is high compression bad for boosted applications? Does it make a difference turbo or supercharged? How can he lower his compression?




He can lower his compression by using a thicker head gasket.
 

4thStroke

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Quoting James:
He's not being cheap, he has $2000 to spend on his build. He wants the 14b because he likes the feel of it in my car, and it's cost effective, good for low end boost, and with some customizing can be used for higher boost.

For the learning process, why is high compression bad for boosted applications? Does it make a difference turbo or supercharged? How can he lower his compression?



$2000 is not much for building a turbo car. $2000 is cheap.

High cylinder pressures cause detonation, detonation is what kills a motor.

Running a thicker head gasket will only help so much, probably not enough to take a high compression NA motor to a safe level for boost.
 

Vr4junkie

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Well I'm no expert but seems like that motor is going live a short life.

I know a few people that have turboed SR20 N/A Engines but max boost was like 6psi and anything higher than that will be shorting the engine life. Not sure on the compression on the SR20 but I don't think its as high as 260
 

James

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How is $2000 cheap for a basic turbo build?

14b- $150
1gBOV- $40
Evo8 IC- $100
Custom IC piping- $200
Ex manifold- $200
WB/boost/oil pressure gauges- $300
SAFC- $150
Injectors- $150
FPR- $150

That leaves him with $500 for misc shit...

Am I forgetting anything?

But if it's jut not possible with his high compression then he can just cam the shit out of it and take advantage of what he already has.
 

LIV4PSI

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You are missing several things

Custom oil and water lines for turbo
Fuel Pump
Manual or electronic boost controller
External wastegate to allow a 14b to run 4psi max
Hondata (SAFC are the cheap way to go)
Gaskets and fluids
Half size radiator?
Downpipe and catback exhaust
Professional tune
stronger clutch for higher power levels
 
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James

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His downpipe is being made by the same guy making his IC piping for next to nothing (just a lucky "nice to know people" moment). He has a half size rad and upgraded fuel pump and a monster clutch setup already. So the only thing I'm missing is wastegate. I assumed the 14b wastegate could be modified in some way to lower boost, of not than so be it! The coolant lines and such was in the Misc- left over money. He has a pretty big stash of Vacuume and braided lines/fittings.

But again this is all irrelevant if he can't run boost on that high of conpression.
 

theevozero

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You would have to lower the spring pressure of the wastegate actuator to go below 7 psi. Which is not really possible.

I've seen stock s2k engines make an excess of 800whp. With proper tuning software and a knowledgeable tuner, you should be fine. Using an safc only, is begging for failure on this setup. Without direct timing control, you will likely be picking pieces of piston out of the firewall. I would not even attempt this without Hondata or an Aem.
 

James

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I'm sure i could talk him into getting Hondada. He has a extra $500 buffer incase of "oh shit" moments, and we have some pretty good tuners down here in Florida.
 

TomN

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He should consider alcohol injection with such high compression.

Or put some cams in it and spray it.
 

James

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Ok so let's changes the direction of the conversation.


How would you build it?

Get some beefy cams, a better flowing exhaust manifold, get a beefy throttle body. Ect ect
 
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