compression ratio question and need ideas

[2, 40oz]

Im looking into getting a gt2871r .64
My current setup is

s14 SR
CP 9.5:1
cosworth Headgasket 1.5mm (im 90 % sure. penny test)
stock everything else
i just got the Z32 maf and currently looking for a deal on some 550+ injectors
some 260-264 in & ex 11.5-12mm lift cams
ill probably keep the stock intake manifold
i dont know if i should upgrade to magen exhaust manifold or just keep stock exhaust manifold hmmmmmmmm
currently i have a AFC neo (sucks) but when all is said and done im getting my ecu tuned by Emphaty
My goal is 340ish whp maybe more but i dont want to pass the stock rods hp rating (400hp) or should iii....:jerkit:


My main concern is the pistons, i don't want to blow my engine by applying too much boost on that compression ratio. So should i just get a S15 turbo instead?

This is my first build so i want to get it right.. any advice is greatly appreciated. :x:

[punxva]

you will be fine with a good tune. plenty of people are running this setup without any problem

[s14unimog]

There are a few things I would like to comment on here.

First of all, I wouldn't consider swapping to a Megan manifold as an upgrade. Typically those equal length tubular pieces will give you a higher peak HP number but its stolen from the bottom end of the curve. Personally, I would recommend either a Tomei or just keep the stock one (there are a few PC processes that will actually increase the performance of the stock piece).

Secondly, I don't think changing from a SAFC --> an Enthalpy (correcting your spelling?) is a giant leap in the right direction. I've personally reviewed some of their .bin files and wasn't exactly impressed. It doesn't take a rocket scientist to see, they didn't spend too much time on their maps (lots of repeated values/ symmetrical maps). don't get me wrong though, the fact that you are concern with more than JUST your A/F's is a good sign. My recommendation is for you to research ROM tuners and Standalones instead and just do it right the first go around.

Which brings me to my next comment.

There has been this long said comment that turbo engines NEED a low compression ratio. This isn't exactly true. For a safe bet, you can always offset a lower compression ratio with more boost pressure, but the end result severely sacrifices low end power and the over all performance of the engines power outside boost. This brings the discussion back to the tune system. without proper control of the management system it will be easier to cause some sort of catastrophic failure. I think you need to go back and do some homework. Unfortunately it doesn't seem like you have a good grasp of what's really going to happen under the hood of your car and possibly "hope" that with a known re-flashed ECU all will be good. I can't tell you exactly what power goals you will reach, but if you tune that engine properly, and everything else is constructed correctly, then I can guarantee, with that setup, you will have a responsive/fast car to play with.

Some food for thought, Enjuku Racing has SR20's with compression ratios above 10:1 and are making close to 500whp

[2, 40oz]

Thanks to both of you +1. i will look into getting a P-fc or something similar, some good tunning instead of getting my ECU tuned.

One question
i currently have a unknown MAF on my car so i dont know the proper in and out settings on my afc neo. would it be safe to install the z32 maf (2in,5out) without getting injectors for the time being?

[fliprayzin240sx]

The MAF setting wont affect anything on the injector side...you can run stock injectors with a Z-maf no problem.

My recommendation for you, dont bother getting the 550s, get yourself 740s. You'll be pushing those 550s to their limit with your setup. I've seen 550s max out at 310whp with a PFC.


As far as your pistons, I wouldnt worry much about it. Its all gonna be dependent on the tune. The only thing with the higher comp is that you wont be able to run as high as a boost level as compared to running stock comp.

[2, 40oz]

ok good i will install my maf today..
yeah i figured i would need 740s

So with the 9.5:1 compression what amount of boost do you think is safe
and doesnt my head gasket 1.5mm drop the compression a bit?

[s14unimog]

So with the 9.5:1 compression what amount of boost do you think is safe
and doesnt my head gasket 1.5mm drop the compression a bit?

I agree with the statement above, 740's are where you'll want to be, esp. since you haven't purchased anything.

To answer your question, yes, a 1.5mm head gasket will lower your compression a bit, but its not a lot. If you figured the cross sectional area of a cylinders difference between the stock head gasket thickness and the 1.5mm one, and converted that into CC then you could see the difference. With higher compression you'll find the need for much higher octane fuels, at comparable boost pressures to a lower compression motor, but this can all be determined on the dyno. Just make sure you monitor knock and don't be quite so aggressive with your timing adjustments. I really think you'll be surprised on how fun the car will be to drive, after everything is said and done. Once everything is done, you might want to be a little careful about running higher levels on hot days, esp. without the proper octane.