Hey all,

So, I did a search of the forum and really only found one thread that addressed it and there wasn't really much of a consensus (though I guess that's expected). Anyway, I just got a 75 with a 350 (and only 56k miles!!!) and I'm trying to figure out which would be the best octane of gas to fill it up with. The owner's manual says 91 but that was way back in 75 when gas didn't have nearly the same kind of additives and such to make engines run better/cleaner. So, can I get by with 87? Should I use 91 as the book said? Any advice is appreciated!

 

87 should be fine. Compression was waaay down by then. I always ran 87 till i put in a built motor. Really just depends on what has been done. If bone stock you are wasting money using higher octane.

 

Listen to your engine while under full load. If it does not ping with regular fuel, stay with regular gas. If it pings, check the spark timing, and if correct, then try mid grade.

 

Hey, sorry, I was out of town when you wrote back and just totally blanked on it when I got back. So, I have been running it with 87 - the engine is really just stock, only had 56k miles - and it's been fine. No knocking, not running badly or anything like that. So, thank you for the input, I appreciate it!

 

Hey Pete, thanks for the tip. I have been running 87 and haven't been having any issues with pings, knocks, gremlins, or anything else. Thanks again!

 

sometimes it not about the knocks and pings, unless you just want to save a couple cents on gas. you said it yourself, the gas back then is different than today's gas. it has all kinds of additives and ethanol in it. it's total crap compared to gas from the 70's on back. what happens to gas when you leave it a can over the winter and don't touch it? it starts to turn. i've cleaned many push mower carbs just because of this. the lower the octane the worse the gas turns. 87 might run fine but it won't be as clean as 93. i run super in everything i own now. cam 2 in my quad. i also blend cam 2 and sunnoco 93 in the Challenger and Z28. when that ethanol came out, we had all kinds of carb problems. now that i blend in the cam 2, no more carb problems.

 

I'm just the opposite. I run 87 octane in everything I own, and I build my engines to run on the lower octane. Only time I run higher octane is when I'm taking one of my hotrods to the strip to go racing.
These both run great on 87 octane, 10% ethanol and no detonation or pinging.

 

Ya know Val I have neve looked at the thread for your Falcon? I didnt know it was driving really. Looks like a monster.

For the record I would guess the motor is 8.5:1 and that is what determines the octane rating, mostly at least. You could run more timing with higher octane but not really gonna gain much.

 

Yeah, it's a bit of a beast, and really too much engine for the '63 Falcon, or the 10" slicks. It's tough to even hook up in 1st or 2nd gear on the 4 speed. Both the 327 SBC and the 464 BBC pictured are around 9.25:1 engines.

 

that's a sweet engine

maybe it's a compression thing. the 350 in the Z and the 440 in my challenger have 11:1 compression. i can definitely feel a difference in power when i use a higher grade octane. they love 110.