I'm in the final stages of putting my LSV together. However, at the last minute I've started to consider CTR 81.25mm pistons over the pr3's i have. With my GSR head, it looks like my compression ratio is going to be around 12.3:1. Is this safe on 91 octane? At what compression ratio due you start getting out of the range for pump gas? Thanks ahead of time!

 

maybe if it was around 11.5:1, but 12.3:1 seems to me you should use 93 or 94 if you can get it. otherwise the tuner may have to compensate with pumping more fuel in the cylindar.
At 12.5:1 gasoline is best not from pump, but high octane like 96. Actually Sunoco's website has a guide to all of this just check it out and examine it for a while, and you'll know just what to do.
Ethanol is another choice here, but more fuel is consumed in ethanol than gasoline in a like engine.

 

Well they changed their website around, but I look around for a fuel & cr calculator.

 

Thanks for the info. I felt pretty safe with the pr3's @11.5:1, which is why I originally bought them. After talking with my buddy though, he suggested that I go with the CTR's and informed me that I would be okay on pump gas. So I just figured I see what others opinions on this were.

 

My build has pr3's & P72 head and run 11.5:1 cr on 93, tuner says any pump premium will work. Here is a url to VP Fuel:

http://www.dmperf.com/vp_fuel_specialty_fuel.htm

 

You can run pump gas at that compression ratio with a good tune, although it will not give you much room for error. Big cams will help a little bit.

Keep in mind that as you increase compression, you need to pull timing so, in the end, running higher compression may not actually net you more power.

Personally, I like running less than 12:1 on 91 octane. You are right at the upper limit of what I personally feel is safe.

 

Here's my current setup. Like I said I am up in the air on the pistons.
65mm tb
sk2pro im
MSD 370 inj
hondata im gasket
GSR head with supertech dual springs and titanium retainers
sk2 stg2 cams with adj cam gears
everything is port matched
stock guides and valves
mild p&p
arp head studs
b18b block
either stock bore pr3 or 81.25 ctrs
stock ls rods shot-peened, polished w/arp bolts
stock ls crank
acl tri-metal bearings
type r oil and water pump, timing belt
act streetlite flywheel
act 6 puck sprung clutch
gsr tranny

 

With a B18b block and GSR head CTR pistons WILL hit the head.