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what octane gas do you all run in your big block chevelles? what should i run if i have a 396 big block?

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15K views 23 replies 12 participants last post by  temp2c  
#1 ·
i’ve been messing around with 89 and 93 octane. i can’t really tell a difference. even if my car could run on 87, i wouldn’t feel comfortable, should i continue to run 89 or start only using 93. i don’t notice a knock, tick, or performance difference. but if my engine was setup for 93, could 89 really cause any damage? [the engine is not stock, i’m not sure what the previous owner did to it or what vehicle it came from]
 
#2 ·
What's the compression ratio and cam?
Plenty of folks running 87 with decent compression.
There's no need to run higher octane than you need to, it won't help the engine make more power...the only effect it'll have is making the wallet lighter.
 
#3 ·
I run whatever octane is ethanol free. I think it’s 91 around these parts. There’s also a filling station nearby that sells 100 unleaded and 110 leaded “off road” gas. Those, to me, would just be a waste of money. My car has only 9:1 or so compression, so anything above 91 would be a waste. It’s a 396, has iron heads, a cam with a bit of overlap (lopes at idle), etc. Busted Knuckles is correct, premium gas will lighten the wallet rather quickly.
 
#6 ·
I use non-ethanol 92-93 in my 11:1 L78 396. Even with 38 degrees total timing at 2,600 RPM you cannot make this engine knock or ping. Moderate mashing of the 'go' pedal in 4th gear at 1,500 RPM on a steep uphill results only in a smooth increase in RPM and speed. And the throttle response of a high compression, performance-built engine makes the extra cost of high octane fuel worth every dime.
 
#7 ·
If your engine needs high octane gas, then that is what is needed. Too much depends on compression, cam and heads to make a good call. However with that said it is safer to run premium until YOU can decide if you can get away with regular gas. Remember it is only the difference between what you will pay, not what is listed at the pump. I myself believe that not using premium gas in one of my earlier cars(69 390 AMX) is what caused it to blow up 4 times in one year. That or being a high school kid at that time.
 
#19 ·
The problem with eth gas and older cars with carbs is the rubber fuel lines and carb parts get eaten away if the vehicle sits any extended amount of time and will cause problems, the stuff screwed a carb on one of my harleys up and it was rode every day back when eth was all you could get that I knew of
 
#21 ·
If it's got original heads you need a led additive. Then I'd run NE fuel with an octane booster .
If the heads are ok for unleaded that's exactly what It means. it's ok for unleaded .
What that doesnt mean is that ethanol is good or even ok. I'd run 90 NE and a booster
I wouldn't put corn oil in ANYTHING. Its junk especially on a carbureted motor
 
#24 ·
Depends on compression and camshaft timing events. I have a 1978 454 with 781 heads it runs best on 87. I have the timing set at initial 20, mechanical 18, starting at 1000 rpm all in by 2400 rpm.. No vac advance.. Runs real strong sometimes I wonder whats inside this engine but the seller said the 454 was all stock from a brand new demolished Book Mobile truck. It has about 8000 miles on it now..