1773-1976 Eldorado V8's and fuel type

[64\/54Cadillacking]

I sometimes use 110 octane Race Gas where I live, and it really does smooth out the engine in my 64.

Any of the higher compression Caddies such as the 68-69 Caddy 472's on down, race gas truly makes a difference as the octane ratings are almost the same as they were in the 60's.

In CA, our fuel mixture is much different from the gas in every other state, therefore, I always have to readjust the carb and timing in the spring when the "Summer Blend" gas is added to the stations, and then again during the Fall because the engine will idle rougher, and have less power.

The potencies are different, and it seems as if I am constantly having to adjust something on the carb, especially the idle mixture screws to enrichen the fuel since our gas is so watered down and is less potent than what the rest of you here get.


So stick with 91, actually 91 is fine in a lot of engines and wont do any harm.

[walt chomosh #23510]

I'm sure there are some distributor "pros" in your city that can tune an advance curve to prevent detonation in any vintage Cadillac. I would also ensure that the vacuum advance was working properly irregardless of the year. Like all rubber products they deteriorate and can cause various performance problems.....walt...tulsa,ok 

[TJ Hopland]

Factory when you got into emissions years sometimes had dozens of part numbers for carbs and distributors that all had subtle differences in the 'tune'.   Over time both the OE's and especially the aftermarket seem to condense that into one size kinda fits most. 

I have seen vac advance units that claim to be 'exact' replacements that pull 3x the amount advance they should when tested and compared to what the service manual said was the original.   That much advance will make even the low comp 71+ engines ping like crazy on premium gas which they should not need.   Most people solve that by retarding the whole distributor which usually really kills performance so you end up paying extra for gas that doesn't help and you loose performance.   

I pretty much only now buy 'performance' vac units that have BOTH the rate you adjust through the vac line and the travel limiting cam you can adjust under the rotor.   With those and a tach, timing light, and hand vac pump/gauge you can pretty much dial them in to be an exact match to the specs in the shop manual.     

[dochawk]

I sometimes use 110 octane Race Gas where I live, and it really does smooth out the engine in my 64.

octane level is an "either/or"--either you have enough, or you don't.  once you have enough, detonation doesn't happen prematurely, and any more is irrelevant.

I understand, though (Carl may jump in any second) that today's levels of octane are *high* for early century cars, such as the 20s, which expect about 50

Any of the higher compression Caddies such as the 68-69 Caddy 472's on down, race gas truly makes a difference as the octane ratings are almost the same as they were in the 60's.

Keep in mind that there is a several point adjustment to be made on reported numbers between the 60s and now, do to the different ways its measured--you have to add 4-6 points, iirc, to today's numbers to get the number that would be reported on the same gas in the 60s.

In CA, our fuel mixture is much different from the gas in every other state,

Not quite--Las Vegas and the area around end up with CA gas; we have a single pipeline into town, although there are a few trucks coming in when CA prices spike.

The potencies are different,

octane isn't related to fuel potency; it's about resisting detonation by compression.

As a practical matter, using ethanol, which has 2/3 the energy content/volume of gasoline, *does* boost octane while the typical 10% mix results in about a 3% loss of energy by volume.

When Cadillac went to premium for the northstar, it wasn't about *need*, but because after decades of telling Cadillac owners that they didn't need premium, 90% were still using it.  so as long as it was going to be there, they adjusted timing accordingly.

hawk