Which fuel to use

[Jrsdart]

hi folks, just picked up a 1969 coronet with a 383 engine. I would like to know what octane fuel I should be using? Also should a lead additive be used?
Thanks again.

 

[69clone]

Do you know the specs of the engine? all original? If you don't think it has hardened valve seats I would personally run lead but I did read something awhile backing that mentioned it wasn't necessary on engines with a lot of miles on them. As far as what octane to run depends on the compression. If the valves are tapping try the next octane up. If not you may try the next octane down and see if it does or not.

 

[Jrsdart]

It's completely original engine,low mileage

 

[Ranger16]

The 383 2 bbl was spec'd for regular, while the 383 4 bbl was spec'd for premium.

 

[Ranger16]

If the valves are tapping try the next octane up. If not you may try the next octane down and see if it does or not.

I think you are referring to detonation aka spark knock. Octane has no effect on valves tapping.

 

[69clone]

I think you are referring to detonation aka spark knock. Octane has no effect on valves tapping.

Yes thank you, was talking about harden valves and must have had valves on my mind. lol

 

[Dennis H]

I'd run Shell pump super if available. Try midgrade then to see if if pings.

 

[moparwacko]

IMHO- oh boy.........69 RR, 383,11.0 comp
I only use Ethanol free, and AV gas.
The Ethanol free is 92 octane around here, and the AV gas is LL 100 (low lead) Octane.
Most marinas around here have E Free, but several regular stations have as well.
The AV gas is sourced from my small airport.
I mix mine about 2.5:1
5 gal E Free, 2 gain AV, car fires instantly, no heat issues, best of all it smells like an old hot rod should.

 

[65-440]

El cheapo stuff in my 9.44:1 383 coronet, no problems. Anything less than premium in my 10.5:1 340 swinger, no Good !!

 

[GetX'd]

I run premium in my 440 - but in CA that means 91 oct is the best you can get. I also add some race gas additive that I buy from Summit. It ups the octane level from 91 to 95. No pinging or problems so far. Also have hardened valve seats.

 

[67300VERT]

Comments about racing gas and AV gas are helpful. Yes, the high octane gas without ethanol does make the car run a lot better. Problem is racing gas is Expensive! Around here its $10 a gallon and that's an issue if you want to use it often. I occasionally get a couple of gals of racing gas and mix it with pump premium for my 67 300 with 440 high performance engine.

 

[SublimeSixpack]

It's my understanding that Chrysler's cast iron had more nickle content then some. I wouldn't worry about using a lead additive unless it gives you peace of mind.

 

[ckessel]

Don't forget that the regular when the car was new was about the same as the current premium. Go for premium on old cars and be safe. Also I read some studies done by fleets, taxi/trucking, on the loss of lead in the fuel and it said that under normal diving conditions that there was no appreciable wear issues on the valves/seat etc. But if you have a chance to get them upgraded, go for it since your guides are probably a little loose and the seal might not be top notch from the age of the components.

 

[TRT1954]

Not to hijach this thread, but does ethanol content matter? I can get 92 octane with 10% ethanol or 87 with no ethanol here in NE Ohio.

 

[Ranger16]

Ethanol increases octane, but produces less energy than gas.

 

[ckessel]

Ethanol probably isn't as effective on octane like lead but its all we get now and its way more temperature sensitive. Case in point, look at all the threads with people having fuel boiling issues on the older cars.

 

[Jrsdart]

Thank you for all the replys , much appreciated

 

[threewood]

I'm bumping this for more input....

91 octane w/ethanol vs. 87 octane clear gas. Would I see a difference if I currently run the 91 without issue? Someone explain the RON rating of gas. I want to try out the 87 because corn gas is dumb.

 

[threewood]

I just added 12 gallons of 88 clear gas to about 3 gallons of 91 ethanol. No issues in my 440. Running 22 initial/37 total with soft advance springs.

 

[1967coronet]

I run 87 non ethanol but I have a low compression RV 440 bottom.
I would not have ethanol in the tank and carb if the car is going to be stored for winter ect.
If your useing it and running the fuel through I don't see a problem.
That stuff draws moisture so don't store a car with it in the tank.