fuel selection, What kind of gas? brand? octane? Options

[Carlitos Way]

I'm curious. I'm sure a lot of gas selection comes to personal preference, but I'm wondering what some of the engine builders and long-time techs recommend for the Type IV engines that we run. Would your selection depend on the year? (i.e. smog pump vs. no smog pump?) carbs vs. carbs? brand? octane? additives?

I'd love to hear what you guys have to say on the subject.

Thanks,

Carlos

[IronHillRestorations]

Generally speaking, use the LOWEST octane you can without pre-ignition, unless the car maker or engine builder says otherwise.

Higher octane fuels have more additives to make it burn slower. These additives can end up as carbon deposits in the combustion chamber (top of the piston, cylinder head, valves), and cause pre-ignition which can make an endless cycle; you have to use high octane because it pre-ignites and it also adds more carbon deposits.

Using a fuel additive like the BG products, or Techron can help reduce combustion chamber deposits.

Air cooled engines generally operated at higher temps than an engine with watercooled heads, so carbon deposit build up usually isn't as bad, but it can still happen.

If you want to play Mr. Wizard, take a medicine dropper of regular gas, put the gas on a white plate and burn it. Do the same with high octane, and you'll find the high octane burns slower, has more sooty smoke, and leaves more residue. You'll find a side by side comparison of the two "burns" interesting.

As far as leaded gas, I'd bet my money that is a urban myth. Last I heard "old style" leaded fuel is no longer in production, and it's against the law to sell it anywhere in the US.