octane booster vs premium fuel ?

[Guest classic.car.fan]

Wondering for my 65 deville. Should I use octane booster or premium. as It does not seem to happy with regular gas. A friend of mine has a 72 caddy and puts premium in it. Is this a good idea?

[Rusty_OToole]

10.5:1 compression and unprotected valves and seats suggest premium+octane boost would be a good idea.

Edited April 23, 2015 by Rusty_OToole (see edit history)

[NTX5467]

Back in the middle-60s when I tended to enjoy being around service stations, it always seemed that a Cadillac owner would ask for "regular" rather than "premium" gas back then. I might gently ask how it worked and they all said "great".

In the current nomenclature for octane, "pump octane" of 93 is pretty close to what premium fuel was in the earlier '60s, at 97 Research Octane. So, super unleaded it should be. Might need a slight timing adjustment (down a few degrees) if any "trace rattle" is heard on moderate acceleration.

There are MANY types of octane booster. Some are mostly alcohol-based, which can put more alcohol in fuel that already has 10% ethanol in it. Some do work better than others, but none are really inexpensive. IF you decide to go that route, you might find out what the drag racers are using and go from there. Of course, finding a local source for 100+ Research Octane "race gas" (the local drag strip?) would allow you to get about 5 gallons of race gas to add to the tank of "normal" fuel, which might just do the trick.

The '72 Cadillac should have the GM-mandated 8.5 to 1 compression ratio, so it should do decently well on "mid-grade" fuel or even "87 pump octane" fuel (which is what they were all supposed to be able to use).

Look for "top tier" gasoline, without concern about octane levels, as they ALL have about the same levels of detergents and such in them now. No need to buy "premium" just to get the full load of beneficial additives any more.

NTX5467

[Marty Roth]

I always add an ounce of Alemite CD-2 Lead Substitute, as well as 4 oz of Marvel Mystery Oil for each 10 gallons of gas for each of my collectible cars. I know that some here on the FORUM will say it isn't necessary, but I've accumulated hundreds of thousands of miles on them over the many years we've been touring cross-country without pre-ignition, valve seat recession, or other mechanical complication. I've always been told to use the lowest octane gas on which my engine will NOT PING (the sound of marbles rattling in a coffee can), and using higher-than-needed octane is a waste of money, and contributes to vapor lock. I've also found that it is better to reduce octane in higher elevations.

Your car - your choice - just my $ 0.02 .

Edited April 23, 2015 by Marty Roth
typo (see edit history)

[Rusty_OToole]

I like Mr Roth's idea. In the case of your 65 Caddy you would need to use the highest octane premium because of the high compression engine. If it knocks you could back off the timing a little.

[60FlatTop]

What is it about the way this 50 year old car runs that makes it seem "unhappy"?

I just put Mobil regular in my happy cars. Of course, the same tanker stops at the Mobil station each time.

Bernie

[Rusty_OToole]

65 Caddy compression 10.5:1 requires premium. 72 Caddy 8.5:1 and built for unleaded, requires regular.

[Guest]

I always add an ounce of Alemite CD-2 Lead Substitute, as well as 4 oz of Marvel Mystery Oil for each 10 gallons of gas for each of my collectible cars. I know that some here on the FORUM will say it isn't necessary, but I've accumulated hundreds of thousands of miles on them over the many years we've been touring cross-country without pre-ignition, valve seat recession, or other mechanical complication. I've always been told to use the lowest octane gas on which my engine will NOT PING (the sound of marbles rattling in a coffee can), and using higher-than-needed octane is a waste of money, and contributes to vapor lock. I've also found that it is better to reduce octane in higher elevations.

Your car - your choice - just my $ 0.02 .

That's a good $0.02. On one of my cars I lowered it's original compression from 10.75 to 9.8 just so I could run on 92 octane. When I moved from sea level to 5,000 feet all that was required was 89. On all my cars without Catalytic converters I add two pints of ATF to twenty gallons of gas having the same effect as Marvel mystery oil.

[NTX5467]

Higher altitudes mean "thinner air" and a less-dense "charge" in the cylinders. Hence, lowered octane requirements, plus the need for slightly smaller carb main jets.

NTX5467

[Guest]

Higher altitudes mean "thinner air" and a less-dense "charge" in the cylinders. Hence, lowered octane requirements, plus the need for slightly smaller carb main jets.

NTX5467

Absolutely, although one of my 70's cars didn't need a thing because cars of that era were factory tuned so lean and on the fence of going super hydrocarbon to lean misfire that at 5k feet nothing was required.

[carbking]

Try this link:

http://www.thecarburetorshop.com/Octane.htm

Also, check how your transmission is functioning. When we upgraded our shop truck (450 HP Ford 390 CID with 10.5:1 compression) from an automatic to a manual; octane requirement DROPPED from 91 to 87 for normal driving. When pulling the 18 foot trailer loaded, I do put in 89.

I realize a manual transmission is not an option in your Cadillac, but if the transmission needs maintenance, it may be placing an additional load on the engine.

As to the octane booster:

I have a 1979 Ford factory turbo. For a long time, 91 octane was the highest we had available at the local pumps. I tried every octane booster then on the market to no avail. Tried double strength - still ping. Tried TRIPLE strength - still ping. Gave up on the octane boosters and started mixing unleaded race fuel of 105 octane ar 1 to 5 ratio with 87 octane pump gas. No ping. A few years ago, one local station put in 93 octane. Tried it - no ping. So basically 91 octane plus a triple dose of octane booster did not equal the results of 93 octane fuel.

Don't have sufficient chemistry background to offer an opinion on octane booster; however, the above is my personal experiences.

Jon.

[Guest classic.car.fan]

What is it about the way this 50 year old car runs that makes it seem "unhappy"?

I just put Mobil regular in my happy cars. Of course, the same tanker stops at the Mobil station each time.

Bernie

Ticking and rattling somethings. And it diesels when you shut it off. Also noticed its getting worse than usual mpg it should get 8 or 9 and its getting like 5

[Rusty_OToole]

Should do a lot better than that. A 65 Caddy should be good for 18mpg on the hiway.

Right off the bat you need the best fuel and probably a tuneup. Do a compression test and oil pressure test to diagnose the condition of the motor. If it is halfway decent you should be able to tune it up.

Don't overlook vacuum hoses, they get hard and crack with age. There could be other parts like choke pulloff, idle dashpot and vacuum advance that need checking too.

[60FlatTop]

A faulty thermostat, soft lower radiator hose, or timing issues can cause that. A good plan would be to check all the home repair items; then take it for and exhaust gas sniff.

I remember you had a brake issue a while back. Dragging brakes could make those symptoms happen. I knew of one old Caddy that used to boil its transmission fluid and mysteriously spit it all over the engine. The owner was at a cruise in one night and went back to his car to pull the brake pedal up by hand so the brake lights wouldn't stay on. I had to go to confession because of my comments, Irish, you know.

Bernie