Tech Talk with Colin Comer

“I just purchased a 1969 L88 4-speed convertible. Everybody tells me I need to use racing gas in this baby, or I risk blowing it up. Can it be adjusted to run on premium pump gas?” —BBL, Chicago, IL

First, congrats on buying an L88. They are awesome cars, and I think the performance will be an eye opener. Just remember to aim it carefully before you drop the hammer.

As far as race gas—yes, if the L88 was rebuilt to factory specs, you must use fuel above 103 octane as per the original L88 instructions. Why? The compression ratio of 12.9:1 makes it basically a racing engine for the street. Lower octane fuel will cause the engine to detonate and do serious damage. It won’t literally “blow up” like a bomb, but it could possibly detonate hard enough to destroy pistons, which will likely take valves, connecting rods, and other expensive stuff with them. An internal “blowing up,” if you will.

Unfortunately there is no way to tune the engine to use lower-octane fuel. Even with severely retarded ignition timing, you run the risk of detonation and engine damage.

Here in Wisconsin, there are any number of places that sell 110 octane leaded race gas in bulk. I buy it in 55-gallon drums and keep one in my garage with a simple drum pump, available at any farm or fleet supply store. You might even be able to get one from the people who sell you the fuel. Last time I checked, it was under $7 a gallon for the good stuff. Alternatively, find the nearest drag strip and carry some fuel out in five-gallon jugs.”