# Is 93 octane sufficient for an original 400 engine



## Nitro (Jun 23, 2019)

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?


----------



## PontiacJim (Dec 29, 2012)

Nitro said:


> 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-compression-detonation-134555/


----------



## bigD (Jul 21, 2016)

Can add some Torco Accelerator octane booster to your 93.

https://www.summitracing.com/parts/tic-f500010t/overview/

https://www.amazon.com/Torco-F50001...coding=UTF8&psc=1&refRID=MM2NE59W253MWCECTAFD

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________?


----------



## Nitro (Jun 23, 2019)

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.


----------



## Instg8ter (Sep 28, 2010)

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.


----------



## jayvee53 (Aug 26, 2018)

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


----------



## parrella (Nov 26, 2014)

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.


----------



## GTOJUNIOR (Aug 7, 2011)

jayvee53 said:


> 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.


----------



## Bob Young (May 27, 2018)

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.


----------



## geeteeohguy (Feb 2, 2008)

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!


----------



## GTOJUNIOR (Aug 7, 2011)

FWIW we run JUST V-Power in the '67 as well with no issues.


----------



## geeteeohguy (Feb 2, 2008)

I am very, very envious of you guys who can still buy 'real' gasoline!!


----------



## jayvee53 (Aug 26, 2018)

GTOJUNIOR said:


> FWIW we run JUST V-Power in the '67 as well with no issues.


Apparently, all Shell V-Power is not created equal....the only Shell station near me sells V-power non-ethanol with a 91 octane rating, or at least that's what the pump is labeled as....at $3.44 per gallon I might add...


----------



## 1966tempest (Jul 14, 2015)

I have a 67 GTO engine, I use 93 with no problems..


----------



## Stereolab42 (Apr 6, 2018)

The 400 on my '68 got rebuilt last year and I've had zero problems running it on 91 octane. It was not overbored or otherwise hot-rodded, but they must have done something to make it more friendly with today's gas or surely something would have gone wrong or sounded wrong in the 1500+ miles I've since put on it, right? I've also been told by a shop I trust absolutely to never add octane booster since it can eat through stuff (I forget exactly what they told me but that was the gist of it).


----------



## Ebartone (Aug 18, 2019)

I’ve been running 93 since I’ve gotten my rebuilt 400, 9.5 compression, raiii cam with no signs of detonation or ping, idles great runs well. But I admit this string makes me nervous......


----------



## GTOJUNIOR (Aug 7, 2011)

The 75# cast iron head on my '66 Sprint is not much different then those V8 heads. The OHC's run hotter then hell and suffer the same effects as such, so Shell V-Power is IMHO a great choice. It's all about tuning your engine and it works well right out of the pump.


----------



## LarryK (Aug 20, 2019)

My '70 GTO has the base 400 with (fresh rebuild .030 over), 10.25 CR but added the RAIII cam. Heads received hardened seats during rebuild. Currently running Sunoco Ultra 93 Octane. I just use Stabil360 for freshness and ethanol purposes. No issues encountered during general cruising and the occasional blast through the gears. Idles fines and runs great.


----------



## geeteeohguy (Feb 2, 2008)

Stereolab42 said:


> The 400 on my '68 got rebuilt last year and I've had zero problems running it on 91 octane. It was not overbored or otherwise hot-rodded, but they must have done something to make it more friendly with today's gas or surely something would have gone wrong or sounded wrong in the 1500+ miles I've since put on it, right? I've also been told by a shop I trust absolutely to never add octane booster since it can eat through stuff (I forget exactly what they told me but that was the gist of it).


I've run Octane Supreme 130 TEL octane booster for the past 16 years with zero issues in my '65, so your shop may need to do some re-thinking. Octane Supreme by Kemco and Torco Accelerator octane booster are the only two on the market that actually raise the octane of the fuel several points, unlike 104+ and 108+ and all the other products you see at the parts store that maybe boost octane 1/10th of a point. Those will indeed cause issues......coated my spark plugs with yellow and red built-up deposits when I tried them in the '90's. But, adding REAL octane booster will not 'eat through stuff'.....cars have run on tetraethyl leaded fuels since the 1920's.


----------



## Eric Animal (Oct 28, 2007)

geeteeohguy said:


> I am very, very envious of you guys who can still buy 'real' gasoline!!


Long Island NY.....100 octane at the pump.....$9.50/ gallon !!!!:surprise:>


----------



## bigD (Jul 21, 2016)

jayvee53 said:


> Apparently, all Shell V-Power is not created equal....the only Shell station near me sells V-power non-ethanol with a 91 octane rating, or at least that's what the pump is labeled as....at $3.44 per gallon I might add...


Our Shell V-power pump is labeled 93 octane. I think it's now around $3.00. Haven't looked lately. 87 is now down to around $2.20. 

I can now buy ethanol-free 93 for about $3.50. That's what I buy for my bracket car. If it was a daily driver, I'd want something cheaper.


----------



## gtojoe68 (Jan 4, 2019)

I'm running 10:1 iron heads and struggle as well. I have 160deg thermostat which helps run it a bit cooler. I luckily live on the N end of Lk Washington in Seattle Area. The local N Lake Marina has non-ethanol 93 at the boat dock which I can drive right up to and fill up (also lawnmower - but that's a different story). First though, I fill a 5 gal can next door to the marina at Kenmore Air - where they have lovey smelly 100LL for the float planes. Yum - good stuff. They won't let you pump right into your car though, have to use a can. I have found that mixing 4:1 with the AV gas is fabulous. Even 5:1 is just fine. Seeing as the AV gas is $5.30 a gal and the non ethanol 93 super is $4.60 - it can get a tad expensive. But I don't drive my hot rod more than 1000k a year. Probably really only 500.

Anyway - that seems to do the trick for me - otherwise, you have to retard the timing so much your power goes out the window.

J


----------

