With the gas prices rising, I tried regular unleaded gas vs. my normal super unleaded and it starting pinging after getting hot (Nashville).

I backed timing from 35 total to 32 total, and it's fine now, but I have learned that running a 9.3:1 compression 330 iron block/heads won't allow for optimal timing without super unleaded on my combo (carb setup, camshaft, and dynamic compression play a factor, so not true for all builds). I will switch back to super and 35 after burning through this tank.

My engine -> https://classicoldsmobile.com/forums...esults-123475/

 

Try using Stabil (Marine) at every fill up. You may be surprised as how much better it will run. Still use the Super not the Regular gas.

 

What is your regular octane there 87? With 9.6 to 1 and a 204/214, 91 non ethanol was barely enough. With 9 to 1 and a 214/214 cam, 87 with 10% ethanol worked fine with an aggressive timing cure. Talking 22 base, 38 total in by 2600 and 20 vacuum advance off the manifold. I actually had 30 degrees vacuum advance canister on it. The motor liked it accept at very low speeds, I experienced bucking, the 20 degree canister fixed it right up. I am going to be at 9.65 to 1 with a 218/218 roller cam with .039" quench. Our best is non ethanol 91 octane, it will be tuned with a wideband but will probably need 91 and 87 will be out of the question with iron heads.

 

No Ethanol is best to use on any automobile (this was a great mistake by the US government) here you can purchase up to 93 octane with or without ethanol (depending on were you live and your local gas stations) the Stabil Marine is only good if you have to use Ethanol. You cannot purchase any lead additives in the USA as they are illegal. You should not have to modify your timing from the original so i would stick with 91 octane.

 

I have ran 91 on my 10.25 to 1 355. Granted the car is fairly light , has a 4000 rpm stall and 3.90 so it does not see the same cylinder pressure spikes that a fully loaded car would under load. On the flip side I run 87 octane on my 9 to 1 350 on my cruiser and it does not care . It's not only total timing you need to worry about but the rate of advance for the overall wants of the car. For example my car I can run the timing locked at 36 total. but since I do drive it on the street I have a very short curve where it's all in around 2200 rpm . This would not work very well on another wise very stock application or mild application in a heavy car. Just some food for thought.

As far as the total timing goes if you run vacuum advance I wouldn't even set it back . Are you leaving a little on the table perhaps but do you really need it ?. I don't think the engine would run retarded enough to run bad or really affect anything . Since you still run a vacuum advance imo those few degrees won't kill much. I cut back my total timing on my street car and actually much happier. ( 32) I found with 36 total it really was not happy above 4000 rpm and it would labor to 4800. I set the timing back to 32 and it pulls clean to the shift point. My wife races the street car so on both cars my tune has to do both things . I dont make changes at the track between race and street.

 

Thanks Copper, good info, I have my total timing coming in at 2400, and with a heavy car, that might be too much too soon. I have a Hughes 2500 stall, but it's flashing at about 2200, not making enough torque to reach 2500 haha. Car is a convertible and weighed over 4,000 lbs, but I am using a Th400 with a 3.90 rear, so it helps a little off the line. It runs great on 93, so will just pay a little more at the pump, but I am intrigued about your experiences in the upper RPMs with a little less total timing. I will definitely experiment with that

 

Along with total timing.

 

Next time you get lower octane fuel just try something as simple as stiffer mechanical advance springs. Timing sooner makes it leaner if you will. So you got a heavy car with all the timing coming in soon and cylinder pressure spikes due to the load and you are asking for trouble imo. I think a car like yours should be more in the 2800 to 3k rpm range for total timing.

 

Good advice, thanks Copper!