Is 93 octane sufficient for an original 400 engine - Pontiac GTO Forum
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post #1 of 13 (permalink) Old 06-23-2019, 02:08 PM Thread Starter
 
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Is 93 octane sufficient for an original 400 engine

Just bought a 67 gto and didn't even stop to think about which octane fuel it needs. It's an original 400 engine, would 93 work?
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post #2 of 13 (permalink) Old 06-23-2019, 06:51 PM
 
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Just bought a 67 gto and didn't even stop to think about which octane fuel it needs. It's an original 400 engine, would 93 work?
No. You will need 95-100 octane. https://www.gtoforum.com/f12/octane-...nation-134555/
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post #3 of 13 (permalink) Old 06-23-2019, 07:10 PM
 
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Can add some Torco Accelerator octane booster to your 93.

https://www.summitracing.com/parts/t...010t/overview/

https://www.amazon.com/Torco-F500010...9W253MWCECTAFD

Some have reported getting by with just lowering the timing advance a bit, for moderate street driving.

Back in the late '60's, the Musclecar guys in my area would buy cheap gas from our local Rose Oil station, when just puttering around town, drinkin beer. But, if they were gonna do any high speed driving or drag racing, they'd buy super premium AMOCO "white gas". Rose Oil gas was 29 cents. AMOCO was 49 cents, at the only American Oil station in our little country town. I suppose that dates me.

White Gasoline is now called________?
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post #4 of 13 (permalink) Old 06-23-2019, 07:39 PM Thread Starter
 
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A sunoco about 15 miles away sells 110 octane leaded

Or

There's also a sunoco five minutes away that sells 100 octane ethanol free un-leaded. I could use this with a bottle of lead substitute. Probably come out a little cheaper.

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post #5 of 13 (permalink) Old 06-24-2019, 08:57 AM
 
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thats what i use, Comp is just over 9.5, so i top off tank of 93 with 4 gallons of 110 Torco ....she likes it. never know what your getting with the 93, ive noticed differences from different station so i have only 2 i go to.

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post #6 of 13 (permalink) Old 06-25-2019, 08:05 PM
 
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Would it be correct to assume that as long as there is no knock/detonation, the engine idle is smooth and engine temp is good that the gasoline being used is acceptable to the engine operation? Great article from PontiacJim by the way, thanks for that!

John
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post #7 of 13 (permalink) Old 06-26-2019, 06:25 PM
 
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I had been having long time pinging and detonation issues. Trying to get the right mix of gas, lead additive for lubrication, and octane boost, while trying to avoid all the stuff in today’s gas that corrodes parts was tough. I just switched to airplane fuel from local airport. Great octane. Lead in it. And no junk. Runs beautifully.
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post #8 of 13 (permalink) Old 06-26-2019, 07:54 PM
 
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Would it be correct to assume that as long as there is no knock/detonation, the engine idle is smooth and engine temp is good that the gasoline being used is acceptable to the engine operation? Great article from PontiacJim by the way, thanks for that!

John
ABSOLUTELY! I'm still very close to factory 10.5 with my '66 4BC Sprint Cammer and have run NOTHING but V-Power for over a decade with no need for any other magic potions.

JM2C

Cheers.
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post #9 of 13 (permalink) Old 06-27-2019, 09:48 AM
 
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I use pump gas 91+ in mine and have no issues. But I do add a qt of Torco per each 10 gal when I fill to be safe. My engine is original and has never been cracked open except for the drain plugs.

I would be careful with retarding your timing as when you retard it moves the flame closer to the exhaust valve and causes more heat to the Exhaust valves and exhaust manifolds. If you have a factory HO/RA damage to those manifolds can be expensive. If everything is set to spec with your tune and you still get ping at WOT you can try replacing the secondary rods in the carb to add more fuel. This of course is with a stock factory engine, disregard this post if anything has been changed from original.
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post #10 of 13 (permalink) Old 06-29-2019, 05:43 PM
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A Pontiac V8 with iron heads and 10---10.5 CR will need 95+ octane fuel to be happy, especially during the summer when temps are higher. I run race gas in my '65 which has a true 10.75+ CR (milled 64cc heads) on a 389, and even my 9.3:1 '67 will ping on our crap 91 octane on a 105 degree day. I installed 87cc heads on it after years of fighting engine detonation with retarded timing, water injection, etc. I think part of it has to do with Pontiac's combustion chamber design, which creates higher temps. This reason alone is why California Trans Ams in the mid/late '70's came with Olds engines....the Pontiac engines produced too much NOx emissions. I have a '61 Corvette with a hot 383 stroker that is pushing 10.5 CR and it runs fine on 91 octane. Different design. The factory cammer OH6 Pontiacs have a different head design altogether which would account for decent running on today's gas. No such luck for the old iron headed strato-streak V8's!
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