Hi guys,
Just a question to see what gas all of you guys with a similar car to be are using.
In the couple of weeks I have had my 74 Eldo, I have been using High Octane (91) gas.
Is this considered the right thing/the best thing to use on these?
Mine is obviously not fuel injected, but I am just curious to see what others with similar Eldo's are using.
Thanks,
Alan
On my '72, I was using plain Unleaded petrol. The same should be for the later ones.
Bruce. >:D
Whale oil for the 18th century Eldorados, steam for the 19th century ones.
My 69 barely pings on 93, but they did lower compression and I understand the mid 70 cars were far more forgiving.
I use regular in my '71 and '73.
Detonation is very hard on engines. It occurs before you can hear it. By the time it "barely pings" it is no longer detonation. The technical term for this condition is "SEVERE detonation". Modern 93 octane gasoline is inadequate for most old 10:1 or 10.5:1 compression engines. I believe I have written about running my '70 CDV on 100 or 110 octane gasoline available in L.A. What a difference ! You must not run high manifold pressure in pre '71 Cads using modern pump gasoline. Keep your foot out of it. By all means continue to use 91-93 octane gasoline in your low compression post 1970 Cadillac. It is cheaper , and is easier on your engine , and you can use full throttle any time under any conditions. Oh , wait a minute. Did I say "CHEAPER" ? Huh ? Hmmmmm. Let's see. Pump price might be 5 - 10 percent higher. Could you get 5 - 10 percent better gas mileage ? Maybe under certain conditions. Very slow , light throttle , probably not. Higher speeds ,higher manifold pressure , probably. Road and Track mag tested this back in the late '50s or early '60s in a large sample of cars. All , save one , got better mileage on the high octane. The reverse was true with the VW they ran. "VWs" , as old Cadillac Carl used to say , " ain't Cadillacs". Cheaper ? Hey , it's easier on your engine. What's that worth ? - Carl
Alan,
Continue to use the 91 and higher octane "premium unleaded" in your Cadillac. That is what I use on any Cadillac that runs on pump gas unless it is 80's or newer that were designed for regular unleaded. Carl is right, when you hear a slight ping that is bad, and why take a chance.
Enjoy your Cadillac!
It would be great if I had easier access to something higher than 93. I'm running stock timing, with full manifold vacuum. Tried in the past using commercial additives, maybe they help a bit...but not convinced its a huge jump (think I heard .07 octane point per tank). Looked into toulene and other home brews (even mothballs ::)) - they all have seem to have real downsides, not to mention questionable effectiveness. Spent a night reading about running a bit of E85 mixed in with the 93. Just a little freaked out generally about what it will do to the system, and also thinking it would necessitate tuning the carb a little differently.
I don't want to carry a barrel of race fuel around with me. I just really wish there were a few pumps that had 95. Just a little edge. As is, I just try to really stay off the pedal, especially on hills.
(not trying to hijack your thread, Seachange)....
I don't know what the manual for 1974 states, but in my owner's manual for 1976, it states that Research Octane Number 91 unleaded gas should be used.
Research Octane 91 is the same as (R+M)/2 of 87. That's regular unleaded gas at the pump.
Research Octane 96 is the same as (R+M)/2 of 91. That's premium unleaded gas at the pump.
I use 87 octane but I can understand using premium as a rule to avoid any chance of a problem.
I believe the compression ratio on the engine went down from 10.1 in 1970 to 8.5 in 1971 which I think means that different octane recommendations would be in effect for the lower compression engines, all other things being equal. My 1976 is an 8.5 compression and it takes regular 87 octane pump gas. A 1974 is an 8.25 compression and the manual likely recommends 91 RON as well but I don't know.
That's the numbers but each car is unique and might need different octane from what is recommended in the manual. For example, my first car was a 1977 Mercury Grand Marquis with a 402 engine. This engine had a compression ratio of 8 and the manual recommended 87 octane at the pump but it pinged on 87 and I had to run premium. All depends on the car. The manual can't tell you what your individual car needs - the car tells you that.
WTL : What are the downsides to Toluene ? - CC
Too many people suggested that it was a carcinogen, so my concern is either exposure upon dumping some in the tank, or breathing whatever fumes it produces after combustion. Not that other additives, or indeed todays pump gas (or the leaded gas of 1969) is much better.
Quote from: WTL on April 26, 2017, 08:39:45 PM
Whale oil for the 18th century Eldorados, steam for the 19th century ones.
My 69 barely pings on 93, but they did lower compression and I understand the mid 70 cars were far more forgiving.
Ben Franklin's was a hybrid: Whale oil or lightning. :o
Quote from: 7gen on April 26, 2017, 10:43:52 PM
I don't know what the manual for 1974 states, but in my owner's manual for 1976, it states that Research Octane Number 91 unleaded gas should be used.
Research Octane 91 is the same as (R+M)/2 of 87. That's regular unleaded gas at the pump.
Research Octane 96 is the same as (R+M)/2 of 91. That's premium unleaded gas at the pump.
I use 87 octane but I can understand using premium as a rule to avoid any chance of a problem.
I believe the compression ratio on the engine went down from 10.1 in 1970 to 8.5 in 1971 which I think means that different octane recommendations would be in effect for the lower compression engines, all other things being equal. My 1976 is an 8.5 compression and it takes regular 87 octane pump gas. A 1974 is an 8.25 compression and the manual likely recommends 91 RON as well but I don't know.
That's the numbers but each car is unique and might need different octane from what is recommended in the manual. For example, my first car was a 1977 Mercury Grand Marquis with a 402 engine. This engine had a compression ratio of 8 and the manual recommended 87 octane at the pump but it pinged on 87 and I had to run premium. All depends on the car. The manual can't tell you what your individual car needs - the car tells you that.
You are correct, the 1976 devilles manual suggests we use regular unleaded gas in our 500cu engines, and I assume that applies to the 75 years too since that was the year GM began with catalytic converters. I've been using regular gas since Feb 1977 in my 76 and made sure the timing was right on 6 degrees before top dead center; if the timing is not correct I don't care what octane gas you use you will get some pinging. Be sure the timing is on the money and use regular (87 octane) gas and your 75 and 76 should run very well. EAM
Quote from: Carl Fielding on April 26, 2017, 10:57:58 PM
WTL : What are the downsides to Toluene ? - CC
That tetra-eythel-lead is extremely poisonous stuff by itself; I wouldn't want to
be messing with it. I suppose they used a lot of it, plus super refining during
the war; by the end our fighters were running on 130 octane.
Ping can be caused by carbon buildup in an engine not used as hard as mine;
can be removed with the water treatment. And a loose timing chain about
drove me crazy with pinging 3 decades ago, till I figured out the problem.
Getting a tight chain is better than premium. Bruce Roe
The "water treatment"? What is that?
Google Italian tune-up and you'll have your answer.
High BMEP on takeoff during the heyday of the great recips of aviation required Anti Detonation Injection (ADI). A 50/50 mix of water and alcohol was used. The high specific heat of water in the mix cooled the temp of the charge as it changed state from liquid to gas. Sometimes you could see the carbon mess blown out in the exhaust at the right moment. We were taught that the alcohol played no part in suppressing detonation. It was said to be simply antifreeze , for obvious reasons. I have read that the methanol DID contribute somewhat. I cannot pass judgement on this. But I did use an Edelbrock Vara-jection water injection system on one of my Cads. This was a very long time ago. I wonder what the thinking on such systems is now. Anyone ? - Carl
I also used an Edelbrock Vara-jection unit on my 1937 Chevrolet Hot Rod that was powered by a 12.5 to 1 427 L88 Chev, bored out to 440. It used to consume a Gallon of water every 100 miles, but no hint of pre-ignition.
Wish I had kept it as I could use it on my '72 Eldorado to replace having to use a bottle of Octane Booster every time I fill her up.
Bruce. >:D
Quote from: EAM 17806 on April 27, 2017, 12:56:12 PM
You are correct, the 1976 devilles manual suggests we use regular unleaded gas in our 500cu engines, and I assume that applies to the 75 years too since that was the year GM began with catalytic converters. I've been using regular gas since Feb 1977 in my 76 and made sure the timing was right on 6 degrees before top dead center; if the timing is not correct I don't care what octane gas you use you will get some pinging. Be sure the timing is on the money and use regular (87 octane) gas and your 75 and 76 should run very well. The major oil companies state use the grade the car manufacturer report in the car's owner's manual; higher octane is a waste of funds because that specific car does not require it. Be certain, again, the timing is on the money and if it is then you better look elsewhere, not with higher octane, unless you have an abundance of cash to waste. EAM
Carl
I believe the over Boostwith water/methanol injection was the "war emergency" throttle setting.
Greg Surfas
I used Water Injection with great effect in my road car when running 12.5 - 1 compression.
Bruce. >:D
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.
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
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.
Quote from: 64CaddieLacky on October 13, 2017, 01:47:59 AM
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
Quote
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.
Quote
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.
Quote
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