whyt00

I'm just trying to figure out how much compression I can safely run on pump gas. I know that the bigger the cam the more you can get away with, to an extent. I also know that there is a point to where you have to take so much timing out to run it on pump gas that the power gain made from the extra compression is out weighed by the power loss of low timing numbers. I have not decided what i am going to build yet, but I am sick of going slow.
P.S. we only have 91 up here

sintered

The combustion chambers on these engines are very efficient... I used to run an LS1 on 87 octane (factory 10.1:1 compression) all the time and the computer never pulled any timing. Before that I had an LT1, which had 10.5:1 and would ping all the time on 87 and about half the time on 89 (starting around 1/2 throttle under 3k rpm) even with the reverse cooling and 160* thermostat. Gen III+ chambers are a much better design than the old SBCs and much more detonation resistant as a result.

If you run 91 all the time I don't see 11:1 being a problem at all. I kinda remember a lot of LS1s back when I was still in the F-body game running 10.8-11:1 compression on mid grade without problems.

TXSZ66AVLANCHE

iTrader: (7)

My LS1 seriously pings on the cheap stuff.

CHILLLLLL

iTrader: (3)

I'm at 11:1 in my truck and I have no issues. I'm putting together a turbo kit right now as well to run on my current setup. You can get away with a lot if you have a good tune.

budhayes3

iTrader: (19)

As you mentioned about the cam, you can run a lot of static compression if you keep your dynamic compression ratio within check. A "bigger" cam with a lot of overlap will help give the cylinders a natural EGR effect and bring your dynamic compression ratio down. If you want to squeak a little more out of it, make sure that your EGR system is operational as it will actually bring cylinder temps down and help prevent pinging.

whyt00

Awesome piece of information I never would have thought of that. Thanks
I was really hoping to get 12:1 I really want to get as much naturally asperated horsepower on pump gas as humanly possible, and then spray the crap out of it

TXSZ66AVLANCHE

iTrader: (7)

So...with a larger cam I can use the cheap gas with no detonation in my LS1?

00ChevyScott

iTrader: (10)

Pinging is most likely due to your tune/tuner


If the timing curve is based on 93octane gas, that's why you're having trouble.

MikeGyver

iTrader: (5)

Just posting in case you didn't know that high altitude needs less octane and you can have a lot higher compression, if the "up" in "up here" means at altitude.

TXSZ66AVLANCHE

iTrader: (7)

Posted that question just for you Scott, Dyno tune is in the works.