hell ya, I have a little over 11:1 and run just fine with a 351 and H/I/C

 

My 306 with aluminum heads is about 9.8:1. I run 93 just to be safe and have never once hear the hint of a ping.

My 351 is 9.5:1 with cast iron heads. Granted it's in a 4x4 F150, but it's the pinginest damn engine I've ever seen. I can't set timing for power and use vacuum advance. I run 93 in it as well, anything less will ping on the highway.

You should be fine though.

 

I had somewhere between 10.5-11 to 1 in my mustang with the 331. I put over 15,000 miles on it with 93 octane and was fine, never had any problems with it. I could have lowered the timing to run 91 octane, but that might have slowed it down a tad.

 

I think it would depend on your cam, heads, etc. the thing that causes detonation is cylinder pressure, not necessarily compression. A general rule of thumb is 180 psi of cylinder pressure for a stock type motor running on pump gas. There have been people that could run like 200psi on pump gas because their heads flowed really well along with other variables. If you have a stock cam you may run into problems with 10.1 compression because there isnt a lot of overlap to bleed off pressure. If you are running a big cam I wouldnt think about it twice.

 

So GT40-P's and an E cam should flow enuff for 10:1 comp?

 

I would think you would be in the clear, but I don't know for sure. I've been reading a lot of books, but I haven't got a lot of personal experience with specific combos. Does anybody know the cylinder pressure with a similar ecam setup? You could prolly do some sort of math to figure out the pressure with increased compression ratio.

 

Don't forget to keep quench in check.

I'm running 9.78:1 on 91 just fine. I still have to tune it though.

I was aiming for 10.25:1, but came up a little short. Time for somemore milling.

Greg

 

Static and dynamic C/R are different animals. Dynamic depends on the cam you run and rod ratio.
Like Ryman said, 180-190 psi on a cylinder compression gauge is OK.
You can generally run about 4-7 pts. higher with aluminum heads.
If you ping, you back off the timing.
Here's a good link: http://www.grapeaperacing.com/GrapeApeRacing/tech/misccompratio.cfm

Ed

 

Not to Hijack this thread but would anyone wanna take a stab at what my compression is? stock block 302, stock pistons and afr165 milled to 54cc

 

Some of the math is real good, something to have in your hip pocket.

It figured out real well, never thought about using the manifold pressure for calculating VE before.

Guess I did OK, seeing I have an engine thats turnning 121% VE....

The swept volume of the cylinder after closeing the valves is very good for calculating a "static" semi dynamic compression ratio. But unfortunatly its going to calculate in error, as the cylinder will fill above 1 atmosphere before compression takes affect with the ram air charge of the intake.

Using static numbers of comparrison for engine builds will net you a "reasonably" safe number so long as equal build technques are used.

As has been stated above, so long as careful consideration to quench is built into the engine. The timming curve and advance mechanisms are properly mapped, and the head material is known you can build a better engine than the average junk yard slap together.

91 octain gas, quality pistons (consider thermal barrior coating the combustion chamber and piston top and another 2 points compression can be built into the engine) propper quench, and a conventional aluminum wedge head and 11-1 static compression is not a problem.

Engine masters compettition that was held (is still being held) by PRI publishing has some engines running 91 octain that are in the "rummored" 16-1 compression range.