11:1 Pistons for 283

[Bob B.]

Re: 11:1 Pistons for 283

Hi,

Thanks everyone for the great info. My use is for a '57 Corvette that raced back in the mid-60s that I am restoring to as-raced (see pic of '66 Enduro at Riverside attached).I'm shooting for American Heritage, so I probably won't be racing the car, but I still want to make the engine correct. Maybe I'll hit it a bit if I drive it to an event nearby, though.

As for OCTANE, I have question. I am running a crate '70 LT-1 350/370 in my '60 right now. I thought that the compression was 11:1 and I use 93 octane and drive it everywhere with no problems, knocking or run-on. Some people say I need racing gas. Others don't. So, what's the scoop?

Thanks,

Bob

[Duke W.]

Re: 11:1 Pistons for 283

This has been discussed a zillion times, and I covered it in detail in my San Diego presentation, which is on the Web.

Today's 93 PON is about equal to sixties vintage 98 RON, which is within the range of the average leaded premium back then.

As a result, most OE "11:1" engines will operate detonation-free on today's premium.

As-built, most OE engines had actual compression ratios about half a point lower than advertised. If you disassemble an "11:1" OE engine and take all the measurements to compute CR (an article about this was published in The Corvette Restorer a few years ago and in the St. Louis chapter newsletter, which is on the Web), it will very likely be closer to 10.5 than 11:1.

Very few owners of never rebuilt OE "11:1" engines report detonation on today's premium, and many OE engines that have been rebuilt with "lower" compression ratio can operate on 87 PON unleaded regular.

People who say you need "race gas" for OE "high compression" vintage engines are clueless.

If an engine operates detonation-free on commercial gasoline - either regular or premium, you dont need anything else.

Duke