Can somebody explain this to me... is it the lower the number the more boost you can run or is it the higher the number???

 

Lower compression allows for more boost.

 

Lower compression for more boost.

When you add all that extra air into the motor it creates a crazy amoutn of total compression of like 16-18.1:1 compression so by lowering your compression you can add more air into the motor before hitting that total compression threshold and detonating.

My truck for instance with a static CR of 9.5:1 and 13psi should have a total effective CR of 17.9:1.

With my new heads I might be at 8.7:1 CR and it would take between 15 and 16psi to hit the same effective CR of 17.9:1......

Or I could run the same 13psi and have a safer effective CR of 16.39:1..

Does this make any sense at all?

 

Here is a nice basic graph for everyone that I keep handy:

 

That makes perfect sense... now my question is what is the "total compression threshold" of a 5.3???

 

I asked the same question in the forced induction forum and it seems it really comes down to your cooling and fuel. If you can somehow keep things cool and use good intercooling and fuel then getting into the 18:0:1 range isn't too bad but I doubt we could go a ton higher. I don't really know. As you can see I was at about 18.0:1 which is supposed to be the threshold for a street car and I can honestly say that I am not sure why my motor let go. was it due to detonation? Was it the loss of oil from the faulty device? Was it the gravel I got in the motor form the fire? I will probably never know but I will damn sure be a lil more on the safe side next time.

Also, don't tune on Meth then run water

 

In my opinion, on a pump gas 93 octane non-intercooled system, you should only attempt 10psi first...with or without a knock gauge. The other S/C systems for the LSx type motors only pump out this much boost for a reason.

Now, once you get some type of scanning device to monitor knock, as well as, some type of intercooler and/or some type of alky inj., then I would say you might try and push it to 12 - 16psi on your motor. ALWAYS MONITOR FOR KNOCK...BE SAFE FIRST.