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View Full Version : sr pistons 8.5:1 or 9.0:1 ?



EMC2
08-10-2008, 10:16 PM
i searched with no real luck to my answers. im rebuilding my sr i would like to have more lowend response. my set up is 740cc gt2871 .64 bc 264cams. intake manifold. z32 maf. how much boost could i run with these pistons and 1.5mm or 1.1mm headgasket? do i need to retune for the pistons or can i run my current tune? what headgasket thickness is preffered? any downsides/insight? or should i stay with stock comp pistons thanks.

I_Heart_Silvia
08-11-2008, 02:57 PM
You would benefit from having 9:1 CR pistons by having more power with less boost, also, slightly faster response overall. This will help with the low-end response you're seeking. I would ditch the IM and retain the stock one if low end is your goal. Any time you alter aspects of your motor you should get a re-tune, especially after changing the CR.

nissanfanatic
08-11-2008, 03:28 PM
The 8.5:1 pistons will give you leadway to run more boost on pump gas.

EMC2
08-11-2008, 04:01 PM
will the greedy intake manifold hurt low end greatly? and what kind of boost could i run with these pistons? will the extra boost posibility of the 8.5:1 pistons give me higher hp mumbers or could i make the same or close to it with the 9.0:1's? thanks

TS4l
08-11-2008, 04:36 PM
I'd keep the intake mani and run the higher compression ratio. The 9:1 is a lot more responsive and takes less boost to make the same power. Why run more boost and stress things out if you don't have too. The IM will hurt low end power but the higher compression ratio will help, but with the IM you'll have more room to breath up top. I think the 9:1 and IM match your setup nicely and should make for a nice flowing set up that will make power to around 7000 rpm's.

You should stick with the 1.1mm HG unless you decide you want the lower compression ratio. That is stock thickness, going any bigger will just drop the CR. I actuall run 9:1 with an Apexi 0.8mm gasket and its sweet. I hit 18 psi at 4000 rpm's with a gt30R.

EMC2
08-11-2008, 04:57 PM
ok well last question do i have to re-tune for the .5 higher compression? i have 2 ecu's for my set up one r.s and one redline tuned. will i be able to run these on my tunes for 8.5:1? thanks

master chief
08-26-2008, 04:26 PM
You rebuild the engine, change pistons (even if you keep he same CR), etc.... its always a good idea to have a quick retune.

You dont HAVE to, but you should - especialy if you are looking for maximum power.

Big_Bronze_Rim
08-27-2008, 10:36 PM
9:1 without a doubt.

sr20goofus
09-02-2008, 07:20 PM
i have been running 9.0:1 for 2 years now, and since moved up to 9.6:1 with my new engine this year. Very responsive ,i am running a much smaller turbo and smaller cams, but overall it has torque down at low RPM and does not have bad spool-up by anymeans. I use my setup for roadracing btw and do my best to stay out of low gears which means low end torque is a must for me.

sorce
09-03-2008, 05:47 PM
i have been running 9.0:1 for 2 years now, and since moved up to 9.6:1 with my new engine this year. Very responsive ,i am running a much smaller turbo and smaller cams, but overall it has torque down at low RPM and does not have bad spool-up by anymeans. I use my setup for roadracing btw and do my best to stay out of low gears which means low end torque is a must for me.

What turbo setup are you running and how much HP?

sr20goofus
09-03-2008, 08:32 PM
What turbo setup are you running and how much HP?

GT2860 turbo @ 12psi, BC 264 cams, 540cc injectors, Enthalpy ECU

270-280 rwhp

i have old dyno chart before compression bump.

http://i42.photobucket.com/albums/e331/sr20goofus/Casey.jpg

hungryjoseph
09-20-2008, 04:05 PM
would you be able to run pump gas? more specificaly, 93 octane

sr20goofus
09-21-2008, 03:23 PM
heck yes.....