IloveNewt

I was talkin to my builder today and we were discussing what pistons to go with. He recomended m actually going down from 9:1 to 8.5:1. He stated that this would lower cylinder presure, would be able to add more timing, and would that i woul dbe able to run higher boost.

I guess the tradeoff is power for tunability/safety. But this is going to be a street car and personally from my knowledge here from HT, it seems liek 9:1 is ideal and perfect for street.

BTW this is on a h23 w/a t3/t4b.

Prod

Personally I'd go with the 9.0:1 for a street car...I'd be afraid 8.5 is going to make it feel possibly too sluggish off boost which is where you're at when you're cruising. Besides how nuts are you going with the tuning anyways...it is a street car like you said and 9:1 should leave you some headroom anyways.

intekragsr

I would go with 10:1 for a street car. If your doing good dyno tuning(every FI should be doing that anyway), 10:1 is perfect for the street. Faster turbo spool, car feels stock(gsr) out of boost, and lower intake temps(dont need as much boost to hit goal power goals)

Some people say 10:1 is high, but there are plenty of Type R's running 10.6:1 successfully.

10:1 is mild, and perfect for street IMO as long as you get good tuning. 9:1/8.5:1 is for serious drag stuff when you are running insane amounts of boost and looking for HIGH numbers. You dont need super high numbers for the street, but im sure you know that.

theres my 51 cents

IloveNewt

Yea thats what i was thinkin too but my builder thinks otherwise. I think i will go 9:1 despite his recomendations. But he did make some points that made me think about how the lower CR would lower the cyl presure and how i could run more timing, maybe make up for the loss of power by running more boost. I can see how a lower CR might be good, ever come around a bad tank of gas it could be nice.

intekragsr

Well this is for the street right? I dont see why you would want a "pig" outside of boost on the street..

How much whp are you looking for? 10:1 wont give you insane cyl pressure..... i dont think...

Who is your engine builder? Maybe he is recommending that low of compression because of his tuning ability and needs a bigger tuning margin? Just a guess.

Anyway to each, his own. Good luck

IloveNewt

About 350whp, but not sure if ill be able to hit that with this turbo. The builder is Howard from AR Fab. Well to tell the truth im not sure of his tunin ability, but from my impression it seems pretty good. He has a 500whp b18 in his race car.
The other day he was tryin to get i thinkm he eitehr said 700 or 800whp....slips my mind right now. But he ended up jusr meltin his block on that attempt. But this wasn't because of his tuning but rather one of his injector's failed.

Type-GS-R-Turbo

Absolutely, go to 8.5:1. I'm running 8.8:1 on my built GS-R, and its not low enough. 8.5:1 would be awesome. You could safely run like 20 psi w/ proper fuel management. Definitely. Read up on RC's website about compression and boost. How low can you go is the name of the game. My car is a little bit sluggish around 2-3000, but as soon as boost kicks in, its stupid fast. Go 8.5, you won't be disappointed

IloveNewt

rc's website?

enginjim

If you are planning on running anymore than about 10 psi boost I would reduce the CR to less than 9:1. If the turbocharger is matched properly there will not be any problems with response. The increase in the usable boost and not having to retard the timing to keep out of detenation will make more power and the response will be there. Compression ratio does not always make more cylinder pressure and more power. More air/fuel mixture trapped in the cylinder will make more power. Lowering the compression ratio and running more boost will accomplish that.

IloveNewt

Rigth now i have a t3/t4b with .63 a/r and a stage 3 wheel on the hot side and a super v on comp side.

Right now w/the JE 9:1 i had we went to around 1 bar on 93 and made 311whp. Dont you think with my small turbo going with a lower CR and higher boost i will be able to make near 350whp? I think i turbo starts wheezing out past 1 bar.

Sonny

I'm running 8.5:1 in my engine and I wish I would have gone with a little higher compression. I don't have the turbo on yet, but the torque is definitely a little on the soft side below 4000 rpm.

I think 9:1 is a good compromise for a street car. It won't be too sluggish off-boost and you'll have a larger tuning window than 10:1 on pump gas.

Sonny

IloveNewt

Well i guess it really has a lot to do with what turbo u got too. I have a relatively smal turbo for my engine and its fulled spooled by like 4-4.5k rpm. Maybe u'll change ur mind when u get ur turbo on.

MotorMatrix.com

do not go less than 9:1. if you are using atleast a hondata system, tuning will be fine at 9:1 for the street. some people are still stuck in the low compression days cause before we were all on fmu. not the case anymore. by the way, 9:1 is still low compression compared to what some peopel are running ont he street.

IloveNewt

Yea im leanin towards stayin at 9:1. We'll see.

Have u had any expirience w/CP slugs?

sweet

iTrader: (5)

i agree with MotorMatrix. 9:1 would be the lowest i personally would use on a turbo street car. any lower and the motor wouldn't make much low end power unless you're running lots of boost. as you mentioned your turbo may not make much more power over 1 bar, so lowering the C/R would most likely not be a good idea if you want to make the most power using the same turbo. keep it the same or increase it slightly to try to hit your goal.

i was shooting for 9.8:1 C/R in my new motor with 84mm pistons, but i ended up going with an 81mm block and different pistons. i got a good deal on the 81mm pistons though they weren't exactly what i wanted as far as the C/R. i didn't want higher than 10:1 but as of now i'll be running 11:1 cause i'm using a stock HG and the head had to be milled/resurfaced slightly. so boost will only be 7-8# instead of the 10-12 i was originally planning on, using pump gas and Hondata.

AlLMoToRvOtEr

I agree with intekragsr on the 10.1 compression if you have a street car make more motor power and less boost power. You can run just as much boost on a 8.5 motor as you can a 10.1 just has to do with tuning.

SIXTYdashONE

10:1, no more comments needed

TwistedHatch

ya i would do a bit more then 9to1 it all depends on your total setup, some people don't understand that a turbo and and engine have to match, you have some people who just put this and that on there engine cause of a name, but everything has to work together.....your compression should be based on your desired boost and your compressor efficiency in my opoinion, and i beleive the turbo your using is efficeint in the lower boost levels, so i would deffinately run around 10to1 just my 2 cents.....

TURBO18

How much boost can you guys run an a 9:1 set up on street fuel? How about 10:1? Just curious 93 octane fuel.

Tinker219

Im a Tad over 11:1. Havent driven or tuned, but I want to see 15 psi. Im anticipating 4-500whp if we can keep it properly lit on pump gas. Might have to sneak it to 20psi on c16

Turbocivic94

I agree with sixtydashone. 10:0:1

Quick 200k Mile Motor

I kinda disagree with anything above 10:1
reason being.. if its <u>street</u>, you'll most likely be using pump gas most of the time. You'll also need that tuning window if you're going for 400+

T-Blaze

Nice thread - Don't mean to jack but I'm just about to build my block and I'm trying to work out the best CR/Pistons for mine.

I have a T3/T04e 57 trim, I plan on running around 16psi with Hondata in my B16A2. hat CR/Pistons would u recommend? I was thinking of JE's 9:5:1??

boosted92

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Quick 200k Mile Motor &raquo;</TD></TR><TR><TD CLASS="quote">I kinda disagree with anything above 10:1
reason being.. if its <u>street</u>, you'll most likely be using pump gas most of the time. You'll also need that tuning window if you're going for 400+ </TD></TR></TABLE>

I agree I think that if you're running a tiny turbo that's going to be topping out at 14-15 PSI, going to 10:1 compression would be useful. When I finally get around to building my car, I'm going to go with 8:1 compression, mainly because I'm going to be using a precision SC61 which is big enough to flow a lot of air and is efficient, because I want to be able to crank the boost up to 20 PSI while i'm driving home from work on the highway if a guy in a Z06 wants some, and because I really think that an 8:1 compression 84MM bore LS/vtec is going to have just as much low end, if not more low end, than a stock LS has, and stock LS power is enough for me for cruising around town.

IloveNewt

The turbo isnt exactly "tiny". just at liek &gt;1 bar it starts to run out of breath.