SR20 from 8:5:1 to 9:1 compression

[gaz_moose]

Ive changed from stock compression ratio to roughly 9:1, am I going to be ok using the car on the current map that I had done for the old compression ratio? I want to put some miles on it before I stick a bigger turbo on it and go all out on the rollers. I don't plan on bashing it off the limiter just cruising it around on the 100RON fuel its mapped for..

its a VVT s14 engine mapped on nistune with s15 injectors and turbo/z32afm,

it had decent (140psi) compression test results when mapped and should have 150/160 across the board now as its brand spanking new.

soo. id going up half a point on CR a real deal breaker??

[hanzbrady]

You could be fine, you could melt a piston.

Or, you could tune the car and know it's safe.

[gaz_moose]

money..it all boils down to money.

tune the car on current setup cost money..which could go towards eventual goals..

buy new turbo cost money..

retune to suit new turbo even more money..

[hanzbrady]

Rebuilding engines cost more money.

[TheRealSy90]

150/160 with 9:1 pistons? My stock unopened s13 sr will do 180 on a compression tester on all four cylinders lol.

[RalliartRsX]

150/160 with 9:1 pistons? My stock unopened s13 sr will do 180 on a compression tester on all four cylinders lol.

Standard compression for a SR20DET @ 8.5:1 compression ratio according to the FSM is 156.......... :ugh:

[mewantkouki]

150/160 with 9:1 pistons? My stock unopened s13 sr will do 180 on a compression tester on all four cylinders lol.

Your stock unopened SR has carbon build up on the tops of the pistons. That's why you're getting 180psi.

[TheRealSy90]

Good, cause it runs like a raped ape.

[gaz_moose]

Rebuilding engines cost more money.


that's why I got no money left. the simple rebuild became out of control.

guess I will just take my chances!! :angel::2f2f:

[Kingtal0n]

I've never tested a used sr20det and come up with more than 130~psi. They all ran fine, great even.

from 8.5 to 9:1 compression is so slight, you won't notice, the computer wont notice, nobody is going to notice. If you think about it in reverse, at 130psi the original 8.5:1 OEM compression is probably down a notch, and it still runs fine. So up a notch, down a notch, same difference.

[TheRealSy90]

Idk, tested mine with throttle body open and 180 on all four.


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[gaz_moose]

@therealsy90... I wonder if you have NA pistons or something.

@kingtal0n... that was where my thoughts lay. ive seen sr20's that still run with 110psi, they were gutless but still ran non the less.

[pacotaco345]

@therealsy90... I wonder if you have NA pistons or something.

@kingtal0n... that was where my thoughts lay. ive seen sr20's that still run with 110psi, they were gutless but still ran non the less.
I just pulled my motor out that had 110 psi and that thing SCREAMED. I just wasn't comfortable with those numbers. Are you on 91 or 93? I'd be kinda wary running 9:1 on 91 octane.. but just don't go driving uphill in hot weather at low rpm and you should be fine.

[RalliartRsX]

9:1 on 91 octane is nary an issue.........especially with the tuning solutions we have. Many new turbo vehicles (non direct injection) run 9:1 and up on 91 octane

Commifornia max octane rating is 91, less we forget (which I see SoCal in your location, so you should be well aware lol) ;)

[S14kouki805]

Idk, tested mine with throttle body open and 180 on all four.


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Excuse my ignorance but are you SUPPOSED to do a compression check with the throttle open?

[pacotaco345]

9:1 on 91 octane is nary an issue.........especially with the tuning solutions we have. Many new turbo vehicles (non direct injection) run 9:1 and up on 91 octane

Commifornia max octane rating is 91, less we forget (which I see SoCal in your location, so you should be well aware lol) ;)
I just re-read OP's post, he's on 100 RON which is like our 93.. But if the car was tuned for his old setup on 100 RON then that's where the issue lies.

OP I'd ask your tuner how balls to the wall he went on the last map, if he left some on the table you should be fine, but if he was on the edge of knock trying to squeeze every last hp out of the car then you might have an issue.

[pacotaco345]

Excuse my ignorance but are you SUPPOSED to do a compression check with the throttle open?
yes messagelength

[gaz_moose]

wait how can you guys have 93 that is 100ron? surely it is 93ron?? man your country is crazy.

tbh it was originally tuned about 8 years ago so my tuner wouldn't remember a damn thing about it. im only going to cruise it around not go balls to the wall so I think I should be fairly safe if I put fresh fuel in the tank when I use it.

[RalliartRsX]

RON - Europe/UK (anywhere outside the US) octane unit
Octane - US octane unit