I've been using regular gas in my 68 6-cyl, and adding lead substitute to the gas. Read an article that said use premium gas with no lead substitute instead of regular gas. What do you cats think about that???

 

Use premium if you're concerned. You may not need the octane, but premium fuels are made from better refining and blending. They have less crap in them and better additives. You'll get less deposit buildup in the long run.

 

unless your having problems with detonation or have the timing advanced just use plain ole regular. if you have the detonation move up to the mid and then premium if need be

 

True about the refining, not so true about the deposits.

Higher octane fuels burn slower and colder. In a high-compression engine, you need this extra fuel stability to prevent detonation. Putting high octane fuel into a car designed to run on a lower octane will cause carbon deposits to build up in the combustion chamber due to the slower rate and colder temp at which the mixture burns. What happens is you don't have enough compression to increase combustion pressure/temp, and you get incomplete combustion. You can counter this to some extent with increased timing advance, but only so far.

Ideally, you want to run the least octane possible without detonation. I run 89 in my 9.3:1 331 stroker all day. 87 causes slight pinging, 91 is simply wasting fuel/power.

Unless you're lugging that I6 all the time, or climbing hills a lot, you shouldn't really need lead additives. Usually the only time you really have valve recession problems is when you put the engine under heavy load, such as towing or climbing hills at low rpm's. Under normal driving conditions, you don't get the kind of combustion chamber pressures you'd need to bury the exhaust valves in the seats.

 

why not use premium in the first place? its obviously better since it costs more.

"well because it costs more! and gas is expensive! blah blah yadda yadda whaaaa whaaaaa"

but is it really worth the $2 you save each time you fill up? unless youre filling up everyweek, then theres not much difference between the prices of the two.

say you fill up every 2 weeks. thats 25 times a year. which means $50 a year you save. not that much. so be good to your car and get premium each time

 

premium is not better unless you need it, other wise you just gumming everything up with carbon

 

well in my case, i need it

 

I work at a refinery. Trust me, premium fuel will leave your engine cleaner. A LOT cleaner in some cases. It's not just burn rate, it's what's being burned. There's often all sorts of crap in lower octane fuels that can't be properly burned in a combustion chamber. Heavier oil ends turn to nasty tar like deposits. The octane rating is also coming from blending additives. Higher octane fuel is not only higher quality fuel, but has additives to reduce the likelihood of detonation, as well as additives to aide in rapid combustion and vaporization. The burn rate difference between 87 and 91 often isn't enough to be noticed on a dyno, provided the premium fuel has good blending for increased burn rates.

Low compression street cars won't have slow burn issues between 87 and 91/93, but once you start talking about 100/130 Avgas, or something like a VP 100 octane or greater racing fuel, then yeah it might affect combustion.

Yeah, running lower octane fuel won't really hurt your car, but premium is better for it in the long run, generally speaking.

 

WHAT IS DETONATION???

 

Octane rattings are more about the compression of the engine pretty much most cars do fine on 87 octane some lose mileage if you use a higher octane then needed.Premium only has a higher octane ratting nothing more and if used on a car that can't fully burn it your just wasting money.All the cleaners and other junk they put in gas is the same on every grade the difference is in what gas station you use each company has there own cleaners they add.Detonation is spark knocking the engine sounds funny timing can fix it most of the time.If i was you id run 87 octane unless it knocks the lead substitute is up to you i know a few with old cars that don't use it and there cars run just fine.