Do I go 12.5:1 or 11.5:1 CR je pistons??

[matty74]

I'm planning a rebuild of my 3.6 for my 911 hot rod project, I am going to run RSR cams and 50mm PMO's.

I need to purchase a set of JE pistons and I'm not sure if what CR to go for.

Do I go 12.5:1 or 11.5:1 CR

What are the davantage/disadvantage with the different CR?

What kind of HP could I expect from this set up?

I'm going to use this for the Street as well as some track days so I want the best of both worlds.

[Steve@Rennsport]

Street use???

11.5:1 for sure,...

[rvanderpyl]

And twin plug I assume

[matty74]

absolutley

[kenikh]

You'd better get big enough cams to ensure that dynamic compression is low enough, unless of course you are integrating engine management w/ knock sensing. The only reason the factory 3.6s used such high CR on the 3.6 was due to the electronic gadgetry that could adjust ignition timing on the fly. If not, you'd better plan on GE80 or bigger.

[matty74]

I'm going RSR grind with 50mm PMO's

[cnavarro]

If going with carbs, you might want to add in a J&S Safeguard for independent cylinder knock sensing and control if you plan on running 11.5:1 still unless you plan on running race gas all the time.

[matty74]

I will be running it on 98 Octiane which is the highest quality one can get i n Australia.

[kenikh]

Originally Posted by matty74

I will be running it on 98 Octiane which is the highest quality one can get i n Australia.

98 octane (Australia uses the RON calculation) won't cut it without knock protection. 98 RON is just below 91 Octane US (ROM+MON/2). You'd be well served to consider dialing your CR back by ~1.5 points, even with twin plugs on those big pistons.

[matty74]

I'll talk to my mechanic today, I'm doing a ground up build so I guess it's a good idea to the Knock protection. Is there a website with info on this product?

[cnavarro]

http://www.jandssafeguard.com/