• Hello there guest and Welcome to The #1 Classic Mustang forum!
    To gain full access you must Register. Registration is free and it takes only a few moments to complete.
    Already a member? Login here then!

What octane fuel are you running?

6

67resto-coupe

Member
I've always been running my '67 with 91 octane, but since I added a "new-to-me" car that also requires 91 octane, fuel bills are going to get pricey. I'm wondering if anyone is running 87 or 89 octane with a similar set-up:

'86-93 5.0 block
GT-40P iron heads, 1.7 roller rockers
E303 cam
MSD billet distributor
tri-y long tube headers
625 Road Demon
Edelbrock Air-Gap RPM intake

Thanks,
Jeff
 
My D-coder has a relatively mild 292 in it and my penchant for building cylinder pressure down low comes back to bite me, even with pump premium, which is labelled 91 octane around here. Guess I better join the modern world and get one of those EMU's or ECU's or whatever they call them. Heck, my early Turbo 'bird can run on regular. No reason why the old naturally aspirated beast can't.
 
This question is somewhat ambiguous, as there are inline 6 all the way up to supercharged race engines and everything in-between. Most engines are designed for pump gas (87 octane), but a few require higher octane ratings. I try to get 93 octane ethanol free, but I can only find 89 ethanol free at a relatively close-by gas station. My 289 4V car has fairly high compression from the factory.
 
Your reply caused me to reflect on if I've ever seen, recently, ethanol-free gas here in Cali. I couldn't recall so cast around and found a site called 'Pure-Gas' which has a database/wiki of e-free stations across America. The list has only nine in California, all 'unbranded'. At one, in Corning, they dispense out of a 55 gallon drum and the 93 octane fuel is 6.89 per gallon. Next time I go to Oregon I'll stop along I5 up there (Corning is right on I5) and see if I can find the place and put some in the Mustang as a comparison.

BTW, I checked OR and there must be over 100 stations which carry e-free. Can't wait to get out of California!
 
Fuel for the 289 on the street was 91 eth free. At the track I ran 110-112 leaded. I've been running 91 eth free in the 302 since last year.
 
What is everyone seeing as a price differential between grades? Around here it has jumped to 20 cents. Wasn't too long ago it was 10. Regular (87) has been hovering around $3.8x for a while now. Premium (93) is 40 cents more.

Reason I ask is the tank cost at fill up to go from 87 to higher octane is not that much. Do the math. Certainly not worth risking detonation and the damage it can cause.
 
"67resto-coupe" said:
I've always been running my '67 with 91 octane, but since I added a "new-to-me" car that also requires 91 octane, fuel bills are going to get pricey. I'm wondering if anyone is running 87 or 89 octane with a similar set-up:

'86-93 5.0 block
GT-40P iron heads, 1.7 roller rockers
E303 cam
MSD billet distributor
tri-y long tube headers
625 Road Demon
Edelbrock Air-Gap RPM intake

Thanks,
Jeff
Click to expand...

Sans the MSD distributor our builds are identical and I find I get the best drive out of 91 octane but I must confess I don't notice a difference between 91 pure and 91 with 10% ethanol. I do agree with Horseplay that the price differential here in South Dakota is not worth the risk of lowering my standards.....paraphrasing of course.
 
I have a completely different engine combo (429 with 10.5:1 CR) but I have to run at least 93 or I get detonation. Sometimes I even add octane booster. Wish I could get 98 or even 95! I don't worry about Ethanol, I haven't had any issues running 10% for several years now. If I knew I could get E85 everywhere I would convert the carb to run it.
 
If you're running traditional 385 series iron heads, that's a fast-combusting chamber and the relatively low MON rating of the E85 could be biting. Have you tried the pure 93? Apparently SS on Bowling Green has it.

This thread caused me to do a bit of catchup on what's been going on, as I used to work in the petrochemical industry and it's pretty interesting, to say the least. What I'm reading about our blends here and my personal experience with the same engine now versus back in the 90's before ethanol causes me to want to investigate further. Sorry if I'm behind. Heck, I still have some 104 octane booster out in the shop from 20 years ago :D
 
I haven't tried E85, but I understand it has a pretty high octane rating. Carb is not jetted for E85, I also haven't tried pure 93 either.
My static CR is 10.5:1 but my dynamic CR is 8.11:1 based on cam valve timing, stroke, etc. I run whatever I can find as I have driven in 16 states now. In Oklahoma I could only find 91 and it did NOT like that. I had to run octane booster with 91. I only occasionally run 104 Octane booster with 93.
 
Everything I have ever seen as far as real testing of those store bought cans of octane boost suggest they have very little actual affect on the true octane level. Most just bump a tankful a tenth or two of a point. Complete wastes of money. I've seen test data that even demonstrates they cause a LOSS of power. Don't waste your money.
 
You must log in or register to reply here.
Back
Top