Whats the highest compression ratio that you would want to run on 93 pump gas before you cause any problems and cause knock?

 

ive seen as high as 12.5 on this board... its all about how much timing your run

 

Also how your quench is set up and what your DCR is.

 

Yea, I've seen up to 12.5:1 but like the other guys said it has to do with a few other things too.

 

I have seen 15:1 on 112....it came out of a pump.

 

All fun aside, but how high do you plan on running? 11:1?

 

I wouldn't run anything past 11.5:1 That would be the highest you could probably run safely.

 

What is DCR? Vaguely famliar with quench, but I have never heard of DCR.

 

Here is a link I found, thanks JRod, that can explain it far better than I can. https://ls1tech.com/forums/advanced-engineering-tech/102153-math-figure-out-if-your-car-will-run-pump-gas.html

 

12:1 - 12.5:1
depends on your supporting modifications.
A heavy, emissions equipped, full operating temperature car will not handle it.

 

Keep the dynamic compression ratio (DCR) below 8.8:1, have a spot on tune, keep the A/F ratio in check, have an extremely tight quench (head gasket thickness minus the piston out of the hole--for very high compression you want this at .030" or lower), and upgrade your cooling system to cope with the excees heat of all that cylinder pressure is creating. If you do all of that, you can run 13.1:1 on 93 with a big enough cam. I run 12.8:1 no problem.

DCR is a function of the ABDC ICA at .006". JRP's cam guide has an Excel calculator so that all you need to know is the static compression (which it configures for you), the cam specs at advertised, and the ICL of the cam. Basically, the MS3, when the static compression ratio (SCR) is at 11.7:1 in a 346cid, has a DCR of 8.5 (pretty safe for 93). This is when it is installed at a 113 ICL, or 113 LSA without any advance. Without the compression, the cam will be down on power everywhere. But because the high compression will make torque down low and power up high, and the cam is designed to rev high and make power high in the band, the overall powerband is very broad with a terrific top-end kick. I'd suggest a quench between .030" and .040" for a SCR/DCR similar to this.

I like lots of DCR, a big cam, and a wide LSA... makes for a very good overall powerband that makes tons of top end power. And, due to the force a high DCR creates (aka torque), it does well in the lower RPMs as well. It also idles very well and has good street manners, because of the wide LSA and high compression. Take a stock LS1, replace the heads with 6.0L heads unmilled, and drive it around. It feels lazy and unresponsive. That's because the SCR was lowered and the cam didn't shrink to keep the DCR up.

 

Good info! I share the same preferences with high compression as well, but obviously you've done your homework.

Jason

 

You can run far above 11.5:1 if the cam has a late enough intake closing point to allow for a 8.7:1 Dynamic compression ratio. Saying a blanket statement like above 11.5:1 isn't safe is clearly uninformed.

 

12:1 here on 93. No problems.