What type of fuel you use in old GMs?

[sarantis]

In my country there is still available the old gas for cars before the introduction of injection that we call "super",the unleaded and the unleaded 100 oct.I asked a friend his opinion about starting using unleaded for my GM 305 (1979-1982)(until now i use the"super") and he replied that maybe it's risky because the old super offers better lubrication for big old engines.
Another guy told me that if i run unleaded 100 oct. my engine will get cleared from detonation and will perform much better.What is your suggestion?

 

[Uraijit]

Re: What type of fuel you use in old GMs?

What's your compression ratio?

Unless you're running some high compression, or a ton of timing advance, just use regular unleaded (87-89 octane).

 

[Bondo]

Re: What type of fuel you use in old GMs?

Ayuh,....

A Question 1st,.....
Is the "Super" just unleaded gas with a slightly higher octane rating,..??..??

Or is it Leaded Gas,..?? If so, What Octane rating,..??

What's the octane rating of your Regular, "Unleaded",..??

Personally,....

I've Tuned my 4.3LX to run Just Fine on the Cheapest regular unleaded Gas I can buy.....

Higher Octane is only needed with Higher Compression ratios,...
Otherwise,.... It's a Waste of Money......

OK,.... I guess that was a Few Questions,...

 

[WizeOne]

Re: What type of fuel you use in old GMs?

In my country there is still available the old gas for cars before the introduction of injection that we call "super",the unleaded and the unleaded 100 oct.I asked a friend his opinion about starting using unleaded for my GM 305 (1979-1982)(until now i use the"super") and he replied that maybe it's risky because the old super offers better lubrication for big old engines.
Another guy told me that if i run unleaded 100 oct. my engine will get cleared from detonation and will perform much better.What is your suggestion?

Your 305 cid engine has an 8.5:1 compression ratio. It would run very suitably on 87 octane unleaded gas all the way up to 9.5:1 compression.

Any higher octane would be a waste as your engine does not have the compression to sqeeze it, hence no detonation if you are set at factory timing. As lower compression cannot get the energy out of higher octane fuels, theoretically you would get poorer performance and efficiency by using it.

As for lubrication, octane has nothing to do with lubrication although it may run some cooler in the cylinders.(simply because it does not fully combust) Old leaded gas acted as a lubricating/cooling/cushioning agent on exhaust valve seats that were not hardened. Your '79-82 305 cid engine was a post lead engine and had hardened exhaust valve seats so even lead is not an issue.

 

[sarantis]

Re: What type of fuel you use in old GMs?

Thanks a lot,very helpful information!