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Runs fine on 87

Paul_G

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Have put about 300 miles on the rebuilt 383 now. First tank was the remainder of the 91 octane gas. Ran that out with no issues. Put 10 gallons of 87 in the tank and surprisingly there were no issues with that. Just put 10 more gallons of 87. I think the 383 is going to be happy with no high octane addiction.
 
It may for a while but once you get some carbon build up in there things will likely change.
I used to be able to run my charger with 89 for a few years when the motor was fresh.
Later on that it started to get predetonation.
Depends what you have for compression, iron heads, weight of the vehicle, stall speed if it's an automatic, how quick your advance is set up etc.
 
Personally, I wouldn't 'trust' the higher octane levels at the pump. Between how quick gas goes bad nowadays, and how few people buy the upper grades, is the gas any good by the time you come along and buy it?
While I 'only' have a stock '77 440 out of a NY'er in my wagon, when I first swapped it in, darn near everyone told me, regardless of year, big blocks need the higher octane. So, that's what I did. One day I found myself at a station that had ONLY 87 octane. Being on fumes and not sure how far to the next station, I put 10 gallons in, expecting the worse.
Much to my surprise, the engine seemed to run better and it didn't ping at all when I stuffed my foot into it which I was getting with 93 octane. Hmmmmm.
Thinking maybe it was a fluke, I switched back and forth over several tanks, and the results were always the same. I ran 87 all the time after that.
All I could figure was the upper grades had been sitting awhile and possibly 'bad'. Whereas 87 is constantly being renewed since everyone buys that.
 
A 77 440 has really low compression maybe 8:1 if you're lucky more likely 7.5 : 1.
It's not the displacement which causes predetonation.
A diesel essentially runs on predetonation (spontaneous combustion)
Your engine was designed to run on lower octane.
 
A 77 440 has really low compression maybe 8:1 if you're lucky more likely 7.5 : 1.
It's not the displacement which causes predetonation.
A diesel essentially runs on predetonation (spontaneous combustion)
Your engine was designed to run on lower octane
.



Which is why I mentioned it being a '77, I understand that. Maybe I didn't make it clear enough that it DID ping at WOT with 93 octane but NOT with the 87.
It did it pretty consistently when I switched back and forth between grades.
That being said, if a '77 440 is pinging with 93 and not with 87, wouldn't that make you wonder about the quality of the gas? I made no changes to the tune, heck, I never lifted the hood.
 
My 383 should be right about 9:1 with 452 Iron heads. The calculation depends on the combustion chamber volume, which from what I have read was very inconsistent. The ratio could be much lower than 9:1. I am running 35* of timing. Time will tell.
 
I have to say I agree with satilite73.
I too have played the pump octane game with similar results.
The higher octane fuel sits for a long time in the tanks.
Locally the stations with "Race Gas" (mostly for boaters round here) get their fuel once a year and must buy a minimum of 1000 gallons.So usually that means fresh fuel in or around May then maybe one year later before it is freshened again.But who knows if it is really fresh new stock ?
That was told to me from the station owner.
 
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