Fuel mix for my 69 Camaro L78

[Chevy454]

Here's my experience with our L72, which is virtually identical to the L78...if you haven't extensively milled the block/heads and have a GOOD set of JE or CE pistons in there then you're compression is gonna be down and a load of octane will actually slow you down.

Our L72 had a stock rebuild by ourselves, and came in at a whopping 10.2:1 compression ratio when it was all said and done...I ran 91 octane (hightest we can get here in town) with occasionally a splash of 114. Our car actually picked up by only running the straight 91...especially if it wasn't just ungainly hot outside. With the low compression and high octane, we never could get enough heat in our engine...particularly in the combustion chamber, but we even had trouble getting heat into the block itself. And we weren't running in some extremely cold climate, it was Memphis in September. Anyway, I tried just straight 91, and the thing finally got some heat in the heads and picked up...you HAVE to have a certain amount of heat in your combustion chamber and block. So, if you've got a basically stock bigblock, a splash of some good stuff might not make optimal power, but it ain't gonna hurt anything...except maybe your ET...just don't go overboard with it.

[sean70ss]

I have ran many types of motors. I have found the best thing is a 80/20 mixture that way it does not break your wallet. 15 gallon tank put 10/12 of 93 and the rest 112 or 116. remember heat kills power if your good with reading plugs you can see where the fuel mixture is. i always run my motors as cool as possiable dyno proves they make more power. Sean

[Zedder]

Good timing on this thread as I am considering building a Sunday driver for taking the family out for an ice cream and am leaning towards a driver quality restored '67 Z. With this particular car, I don't want to mess with mixing fuel etc. and had considered taking the compression down from the factory 11:1 ratio. From what I've read here and on some other sites, this isn't necessary for 91 pump gas? My last Z ran on like crazy when shutting it down and would ping loudly on acceleration - that drove me nuts. Any thoughts on this? Some have said to have the distributor recurved to correct pinging on acceleration. I'd love to learn from some of your experiences...Thanks,

[ssl78]

When I ran my car at SCR7 its was running speeds of 98 and 99 mph all day.I was using 93 octane unleaded pump gas My tank was down to about 1/8 of a tank and Greg who had the orange clone copo Chevelle there had some aviation fuel, I added 5 gals and made another run and I lost 31/2 mph. The burn rate must have been way to slow so I guess more octane isnt always the case.
This brings up a point I have been wondering about I have a L78 Chevelle a L78 Camar and a L72 Camaro I have a hard time to get any one of them to spark knock set at 8 degrees with the stoick distributors. They also seem to run better at 12-14 degrees. does this new fuel even burn slower than the old leaded fuel? I even went out and bought a new timing light thinking my old one was bad. Anybody else notice this.

[Chevy454]

Hmmm...interesting, John!

I tend to worry more about total timing than initial...when you're driving (and especially racing) you will be at total timing for most of the time, while you'll be at initial timing only at startup and idle. You need to find where your engine runs best with the total timing...and what your initial is will depend on how your distributor is set up. If the engine runs best with 39 degrees total, but wants to kick back when you start it, then find what initial works...then you can either sacrifice your total timing or do it right and get your distributor curved. Our cars like 12-14 initial, and depending on compression ratio anywhere from 32-40 degrees total. I've found our lower compression (10:1) L72 likes around 39 degrees while our higher compression L72 (12:1) only likes around 33 degrees. The burn rate of fuels is built into them, which is why there are a gajillion types out there...but generally the race fuels have a faster burn rate, as well as a higher ignition temperature, which help alleviate detonation.

[Mr70]

To all you guys who answered in this Topic.
What Spark Plug size/Brand are you running the 1/4 with?

[Chevy454]

NGK R5671-A...I believe the heat range is "7". AC's killed our engine on the dyno, but when I plugged in the NGK's it picked it back up and cleaned up a couple cynlinders...go with either NGK's (preferance) or Autolites.