Fuel mix for my 69 Camaro L78

[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.

[JoeG]

I did find that the AC'S seem to keep the tune longer for street use, ----At least in my case---Just some info----

[Chevy454]

Joe: does that still hold true today, as in the last couple years or so? The reason I ask is that our engine builder as well as some of the S/SS guys I've talked to seemed to feel like the *quality* of the AC plugs has gone away the past few years, which is why they are all going to NGK or Autolites. In fact, I believe it was Moparts that told me he was at a parts vendor's tech conference somewhere and the AC rep told the crowd that the AC plugs were being made by Champion? On the first L72 we had on the dyno, we made right at 30 pulls with it, and it had a stumble and rough idle with a couple different sets of AC plugs...the NGK's smoothed it out and picked up the power.

[moparts]

Stay away from the "airplane fuel" if it is true airplane fuel it has alochol in it and it will destroy your rubber parts in the fuel system....not to mention it is hard on the aluminum parts too.

For street driving I agree with Sean70ss run a 20 percent or so mix of good fuel. This will help with part throttle detonation and help lube the valve system. Don't tell Rob but there is positions on the throttle other than idle and WOT. With a properly working vac. advance and low octane fuel even 9 to 1 compression engines will spark knock under the right loads.

Just a thought, spark knock, detonation, ping or what ever they call it in your area, could be listed by the surgen general as a almost silent killer of your high compression engine.

[moparts]

Yes Rob it is hard for me a true Bow Tie Guy to admit but you can make almost anything run better on something other than the AC plugs. The new platinum plugs seem to be alot better. It was the champion rep that was bragging they made ac's for them.

[JoeG]

Don't get me wrong--I used NGK'S--Fine plug--And for sure go by your Dyno read out-- I just said in my car the AC's seem to hold a " Street" tune --no rough idle/ slight stumble longer without pulling them out to clean them up--I do have a high output ignition that use to keep the Champions going back when----Didn't mean to push one plug or another--Just something that I've observed in trying different plugs---Nothing is written in stone---Didn't intend to put starch in Moparts shorts--