LT-1 Advice please re: compression

[Mark K.]

I'm starting my search for a nice LT-1 and I'm looking for some advice regarding the various compression ratios offered during '70 - '72 and how they are affected by today's gas. I don't want to mess around with octane boosters etc., so should I focus on the lower compression '72's only? Thanks in advance, Mark

[Terry M.]

Re: LT-1 Advice please re: compression

Those who keep track of these things will correct me if I am wrong, but I believe 1971 and 1972 have the same compression ratio. 1970 is the bad boy.

Duke will tell you the compression ratio is always short of the advertised mark anyway.

[Duke W.]

Re: LT-1 Advice please re: compression

Assuming no engine modifications, the '70 LT-1 can be operated on modern unleaded premium, and the '71-'72 versions will be happy with a diet of unleaded regular. Neither has a spark advance map optimized for performance/ecomony - it was optimized for emissions - and optimizing it for the former will actually REDUCE the octane appetite!

The advertised CR of the '70 is 11:1 and the '71-'72, 9:1.

Actual CRs depend on the individual engine, but most, as built by Flint, will average a half-point lower than advertised, and because the camshaft has a late closing inlet valve, they can tolerate modern gasoline with the as-built compression ratios.

I recommend rebuilding the '71-'72 version with the '70 pistons to get the CR up. It will yield 5-8 percent higher torque/power across the rev range and a similar improvement in fuel economy.

At today's prices, premium is only five percent more than regular, so the fuel cost is a push and the extra torque/power is free!

Duke

[Michael W.]

Re: LT-1 Advice please re: compression

Assuming no engine modifications, the '70 LT-1 can be operated on modern unleaded premium, and the '71-'72 versions will be happy with a diet of unleaded regular. Neither has a spark advance map optimized for performance/ecomony - it was optimized for emissions - an optimizing it for the former will actually REDUCE the octane appetite!

Absolutely! There's plenty of owners around who run their cars on pump gas, ethanol or not, without difficulty or modifications. I'm beginning to think there's some people who want to boast about their cars that supposedly won't run properly on pump as gas a way of suggesting that it's a special 'beast' that can't be tamed.

[Mark K.]

Re: LT-1 Advice please re: compression

Thanks you guys! That makes the search a lot easier

[George J.]

Re: LT-1 Advice please re: compression

Absolutely! There's plenty of owners around who run their cars on pump gas, ethanol or not, without difficulty or modifications. I'm beginning to think there's some people who want to boast about their cars that supposedly won't run properly on pump as gas a way of suggesting that it's a special 'beast' that can't be tamed.

Mike,
I think you're on to something here.

George

[Jim T.]

Re: LT-1 Advice please re: compression

Absolutely! There's plenty of owners around who run their cars on pump gas, ethanol or not, without difficulty or modifications. I'm beginning to think there's some people who want to boast about their cars that supposedly won't run properly on pump as gas a way of suggesting that it's a special 'beast' that can't be tamed.

Mike I let my 1968 L79 327/350 HP 11:1 with original engine sit for a year or so. Did not do anything to the 7-8 gallons of premium in the gas tank. Started right up, ran good on the highway and burned the fuel down to about two gallons before I added fresh premium. I had no problems with the added ethanol pump gas.