Fuel Usage 1967 GTO
 

Hello all and thanks in advance for your help.

I have a basically stock 1967 GTO with the 400 4-bbl and 4-speed transmission. It is occasionally driven and not raced or really run that hard. The last it was driven was in 2015.

When it comes to the readily available fuel at the pump these days, am I better off to go with a higher octane (93) with ethanol, or go with a lower octane (91) and not have ethanol? The four fuel hoses on the car have been replaced with modern hose which is ethanol-resistant.

I am just looking for the lesser of two evils. I live in the Kansas City area, if anyone else is there and knows of a good resource?

Thanks, Olmanwinter

I run the 93 in my 67 GTO ..original born with drive train

From the standpoint of detonation , octane is octane . If your goat needs 93 to stay out of detonation , 93 E10 is it . Does it run safe on 91 ? If it does , I’d do ethanol free all day . My F150 and old 09 civic have more power and better mpg on it . The civic really responded in the midrange . It didn’t need 90 octane at all , it was just the pure gasoline releasing more energy . I haven’t tried it in my GTO because I just don’t think 90 will do the trick and I run 93 ethanol . Letting either fuel sit for years in your tank is going to cause trouble .

I have the same powertrain as you do, and drive moderately but at least twice a month during the April to October driving season. So maybe 200-500 miles a year. I have been using Sunoco 90 ethanol free for over 10 years. I use this fuel in my several 1960's/70's cars. No knock, no problem. You can go to www.pure-gas.org to find the ethanol free gas stations near you. I just looked at Kansas and there are plenty, 50+ for sure in the state. Most octane is 87 to 91. I bet you have one near you. The GTO has a big fuel tank, I think 21 gallons, so that's lots of fuel to use up before you store it for the winter so no ethanol makes sense. However if you do get knock with the 87-91 octane you could try a 50/50% mix of ethanol free and say, 94 octane. By the way, I called up the Sunoco tech hot line when I started to use the fuel. They said that the 90 ethanol fuel is the same fuel as their 91, 92, 93 and 94 fuels, same detergents etc. they just add more ethanol to get the higher octane.

As others have stated, use the least alcohol you can get away with. Lets say the 91 octane no alcohol fuel gives you an occasional very light ping. I would try the 50-50 mix of E10 93 and 91 no alcohol. That would give you approximately an E5 mixture, which is way better than E10 on your carb rubber and fuel lines. In my own car, I have exactly 10:1 static compression, but aluminum Edelbrock heads. It runs great on 90 octane no alcohol fuel which is all that's available in my area alcohol free. I run 37 degrees total timing and 12 degrees of vacuum advance. 14 degrees initial.

USING E10 is no problem. You know...actually driving around, burning fuel, replacing with fresh when the tank gets low.

STORING E10--especially in the vehicle's gas tank and carb bowls--can sometimes be a disaster.

I've been using E10 as my fuel of choice, in Rochester, Holley, Keihin, Mikuni, and small-engine carbs; and TBI, batch-fire, and sequential fuel injection vehicles since 1980. My only fuel related problems were in my boat--filled-up at the marina; the underground tanks at the station were contaminated with lakewater. My small-engine (Weed-whacker, Chainsaw, leaf-blower) fuel supply hoses rotted, which I believe is due to Communist Chinese plastic fuel hoses, not the fuel going through them. And a small generator had the foam in the gas tank rot, which I blame on some dumbass at Tehcumsah putting foam in a gas tank to control slosh, instead of building a better gas tank with baffles.

I've never had a problem I could genuinely blame on the Ethanol.

Have to hi jack a bit ! Now I’m wondering , does anyone think that a 10.1 iron head 406 can get by on 90 ? Or should I leave well enough alone ?

Fuel Usage 1967 GTO
 

Thanks to everyone for your responses.

After doing local research as to what is available, I ended up using ethanol-free 91 octane, with VP Racing's Octanium additive. With one quart of the additive to a tank of fuel, it seems to be doing well. Fully warmed up, I did a pull on a long hill in 4th from 35 to 55 mph, with no problems noted.

I thought that I had a local option for 100 low lead aviation fuel, but that didn't work out. :(

Thanks again for your opinions and experiences.

Olmanwinter

What is the hot cranking compression on your 10 to 1 iron head 406?
This is the starting point of getting a good answer to your question.

Blending 110 LL avgas
 

Not to hyjack thread. I blend 110LL (I think 110) avgas in my original 70 RAlll. Like 25%. Do I need to add lead substitute and MMOil as pervious owner told me to do? Thanks

Adding a lead substitute will surely help the life of the valve seats and valves in iron heads if you drive a lot of miles and or apply your right foot hard a lot.

every time i try going back to e10 i have problems ... pure gas for anything other than a modern daily driver!! lawn equipment, hot rod, chainsaw, dirt bike, use pure gas.

I run E10 93 in my '67. 69 400 with 62 heads and 2802 cam. I would run 93 straight gas if I could find it, but all I can find is 89 octane. 91 straight gas would be fine. Lead additive supposedly helps more with valve seat erosion, but not sure the modern formulations really do anything. I would not add any light oil (marvel mystery, etc) to gasoline. OIl reduces octane and can aggravate detonation.

The most obvious issue I have is gas vaporizing in the holley carb at idle. E10 seems to vaporize more aggressively. The AFR goes into the 11s at idle with air cleaner on, its 13s with air cleaner removed. Only does this when hot, so I assume it's carb vent fuel vapor being pulled back into the engine.. The E10 gas also evaporates really quickly if the car sits. Also, the E10 doesn't color the plugs like straight gas. I've run AFRs into the low 10s and the plugs stay pretty clean. E10 runs about 5 percent leaner than straight gas, so you need to go up 1 jet size when running E10, assuming the engine is tuned properly for straight gas. No audible detonation, no black specks on plugs and no overheating.

AV safe to use & how does it burn ? Did not think it was good to use in street cars.

I ran AV gas exclusively for 4 years in my 64 Lemans with 66 GTO running gear but that was 20 years ago. Don’t know about the formulation now.