Stock Lt1 10.4:1
Stock Lt4 10.8:1

Depending on the gasket thickness I can be anywhere between 11.1:1 to 12.2:1.

What is the most we can go on pump gas?

 

Which pump gas, regular (87) or premium (91 or 92)

In a properly built engine, 91 can get away with 12:1 without any pinging. The less spark knock you can get, the less the timing is retarded by the computer and the more power you can make. A typical engine running 91 octane should stay below 11:1. The only way to know for sure is to use a scan tool and look at the spark knocks under load.

 

Here in NE Ohio we have 93 at all the pumps. We can get 94 at the Shell stations, but mostly 93.

I ran 11.5:1 on my big block Olds. With the reverse cooling of the LT1/LT4 heads I figure 1 whole point above that (12.5:1) could be had.

I know there are many factors that affect detonation (cylinder pressure, cam overlap, hot spots, etc). My cam is ground on a 107 centerline, I believe this works in favor of reduced cylinder pressures due to more overlap.

Using the 0.027 head gasket will give me 0.039 quench area, and I believe optimum quench should be close to 0.035. This will yield a 12.2: cr.

An 0.040 gasket will give a quench of 0.052 and a cr of 11.1:1. This is nealy stock cr but the quench is getting further from optimum.

What's more important, optimum quench or near-stock compression?

 

Also depends on the VE% of the motor... i've seen motors with a low VE run lots of DCR/SCR and be fine, higher VE can cause detonation issues easily.

Now E85 is another story.

Bret

 

9.0DCR is the accepted max. Like Brett said if ya are running 120%VE at 6000RPM's ya might want to back off a touch.
Your cam will determine what STATIC ya have to run to come out with the right DCR

 

A more productive way of reducing cylinder pressure is to delay the intake
valve closing. This has a much bigger impact on reducing dynamic cylinder pressure
compared to increased overlap.

 

Little more than a touch.... run into motors wanting closer to 8.0:1 than 9.0:1 DCR with everything done right and lots of VE%

Bret

 

my zero deck 358 LT1 is at 11.7+ on California 91 4300lbs auto

 

My advice: go with a proven combo. Unless, of course, you have the time, money, and patience to experiment.

Rich

 

Very good advice. I kept band-aiding my combo with bigger cams. I can still make it ping if I try. I certainly can't let somone drive it that doesn't know about the issue. 6th is really easy to ping.

@ 13:1 running 91 pump gas. Think my current tune is 39 degrees of advance up top, but it took a lot of playing at low rpm / high load settings.