Hey everyone, I'm a newbie here but definately not a newbie to SR20s.

So I have an 89 240sx with a blacktop SR20 with a bent rod (actually warped from overheating, long story :( ) but I'm going with Eagle H-beam forged rods.

I'm in the process of rebuilding it and I was wondering if anyone had input on running like 10:1 CR. Now, before you instantly say I'm stupid and it's a recipe for disaster, let me give you my set up.

It's actually a pretty built motor except the bottom end. GT2871R, Walbro 255, Denso 700cc injectors, Cometic HG, 1mm larger Ferrea valves, Sard FPR, Apexi AVCR and SAFC, etc etc etc. I'm not going to list it all, f you have questions just ask :biggthump

But the kicker is I run only E85, roughly 107 octane, also burns cooler. Now, I typically hit 16-18 psi when out and about, but would bumping the CR from 8.5 to 10 or 10.5 and lower the boost to 10-12 be worth it? I know, I could just up the boost, but I'm looking for a more linear curve and I know upping the CR would give me better power below boost.

I've searched for this and really only come up with negative thoughts but other people were planning on running 91 or 93 pump.

Thanks in advance for the help!

I run 10.5:1 CP pistons in my SR20DET, with around 18psi boost (peak). It wont run safely on 102 octane, so I have been running it on MS109 from VP Racing. I have however just bought some bigger injectors to run the E85, I am hoping the E85 will work without turning down the boost.

THe power delivery is fantastic with the higher comp, you can drive it off boost and it still feels really good. Even low boost like 5psi feels great, but when it hits bigger boost - it's lots of fun.

i'm running a 10:1 bottom end. i made 227whp and 217wtq on the stock t25 at 7psi. holds up just fine, no detonation. i am also running 93 octane no problem.

don't worry about compression as long as you plan on getting it professionally tuned.

10:1 on forged parts will be fine on pump gas at low boost 7-10psi. Now if you have a good tune and run c16 race fuel I have worked on and seen(on the dyno) 10:1-10.2:1 c/r turbo cars make 700+whp. I would say YES do it.

yes you can run higher compression with a turbo. many of us have boosted stock 9:5:1 motors and stock ve 10:3:1 motors with no issue. you will have to turn the boost down or run higher octane gas to be safe. With water/meth injection you can run more boost but it will need to tuned right or it will blow up. why not go 9:0:1 and be in the middle.

just search 10:1+boost there are tons of threads on here about HC boosted motors!! DO IT you'll love it!! GL

I know I might get flamed for this, but whatever

I do know the honda boys have been running higher than typical (8-8.5:1) compression pistons on thier daily driven (forged) turbo engines for the past 3-5 years now (seems tuning has gone leaps and bounds in the past 5 years)

I personally think 9 to around 9.5, 9.8 should be good on a proper, daily driven pump gas setup with proper tunning (I am talking turbos bigger than T25 - T28 here. More along the lines of a T3 frame turbo like GT30 or GT35R, Holset HX35, Bulleyes turbos, etc). I can look this up over there and bring over some info on thier setup................if you wish

And again, all in the tune. Simple

Also, look at the numbers stock block S2000 have been running lately

Not certain what it is, but the hot setup is a GT35R turbo with supporting fuel, stock block (head studs I think, if that much) and 12-16 psi of boost. For some reason those engines love boost (11.1 compression, mind you) and reliably hold 400 whp on pump gas

Mase Engineering just put out a kit (or close to) that uses a Precision 5857 turbo, stock block, that made (makes) 420 whp and 250 lb ft or twist (its a honda motor, so that torque is expected) at 14psi of boost.

And it seems these high compression honda motors have been fairly reliable to boot

http://honda-tech.com/showthread.php?t=2651113&highlight=s2000

(P.S, not really a honda boy, but information is information and whatever you can learn to make your life easier, much simpler and more informative, Im down)

I know a few people that run 9.5:1 CR setups with forged internals, and they're easily over 500whp on a 35r. One in particular runs around 22~24psi of boost on pump/race mix, and 20psi on pump.

The car is NUTS. I'd go anywhere from 9.5-10:1 CR and have fun! Easier/more forgiving as far as tuning goes. IMO if you're up there beyond 10.5:1 tuning becomes a little more obsessive to ensure you don't blow anything up.