I don't have to run PREMIUM fuel anymore !

For over 23 years, I've been a slave to the high cost of Premium fuel when I buy gas for this car...



The first 440 was built and swapped in the summer of 2001. It was iron headed and around 9.2 to 1. I ran Premium 92 then...



When the octane dropped to 91, I don't know if I noticed a difference. I built another 440 in 2004, this one with 9.5 compression and aluminum heads but still ran Premium 91. That mill threw a rod at around 850 miles so I got another 440 block and got a 4.15" stroke assembly to get 493 cubes. I was now at 10.8 to 1 and still needed Premium fuel.
Over the years I've dealt with detonation. I've tried delaying spark advance, limiting the advance, making sure I wasn't running lean, bigger cam, thicker head gaskets, higher octane fuel like so:



In 2022, I pulled the engine to go through it after a camshaft went bad and ate several lifters. I took this opportunity to lower the compression a bit but add quench.
I'm now at 9.8 to 1 but I have a quench distance of .040. I've been careful and have kept using 91 octane fuel at every stop...until May of this year.
On the way home from a car show weekend in Van Nuys, the group I was with stopped for gas just off the freeway. Just for the heck of it, I topped off with 89 octane mid grade.
Now, I still run 35 degrees of total timing which is in around 2500 rpms. The engine did not knock at any time but just to make sure, the next fill up I tried 89 octane again.
Still no knock and no run on when I shut it down. It has me wondering if I could actually run it on 89 octane.
I've been careful to always run the highest grade gas for years so being able to get away with cheaper fuel in the lower octane is great! I don't mind paying for the better gas in this car since the car is not a daily driver.
Still, if I can save 20 cents a gallon, that is cool. Also, it is nice to feel okay if I stop at a gas station that only has 87 and 89 octane.
What is the highest compression ratio that you have ran on regular or mid grade gasoline?

You could hear det with your engine using a particular fuel. So you know & can hear it [ hearing still good ]? If do not hear det now with a cheaper fuel, go for it.....
I have seen tests where higher octane fuel made less HP than a lower octane fuel, so no point spending extra $$ if it does nothing...

That is another good point....that it may be possible to make more power with less octane.
I've read for years that you should run the lowest octane that allows you to avoid detonation and that using a higher than needed octane is just wasting money.
Again, it isn't a daily driver. It is a hobby car that usually gets less than 2000 miles a year put on it. Spending 20 cents more per gallon isn't that much when I'm only using 200 gallons in a year. It just feels like a little relief to be able to step it back a bit.

They are so fickle these cars. My GTO had the usual induction system: high rise intake & 4bbl carb. 9.8:1 CR. I had to use 98 octane [ similar to your 95 ] to stop det. Had cold air induction, cool running engine. Could get det on very hot days.

Switched to a completely different induction system, still carbs though. 20 yrs now. Nothing else changed. Car runs on 91 [ about your 87 ] & I have never had it det under any conditions.

What this showed me is how important the distribution of the fuel & air is because when you hear det, might only be one cyl that is detonating because it is lean.

Congratulations! I’m sure it’s the same in California, but I know in Texas we have some pretty small towns that either don’t offer 91, or it’s just a few farmers that don’t need that so who knows how old that gas is, even if it can be considered gas anymore ! Lower octane is more common , and it is cheaper too, but if it’s not a main driver cost isn’t too much of a factor, it’s really also piece of mind that you don’t have to stress out about finding the Goldie locks gas station, you can go anywhere and fill up anywhere

I’ve been using 91 no-ethanol in my old cars for a couple of years now and tuned them all with shortened advance curves to keep base timing up while cutting back max timing a degree or two. They do just fine, even my Vette with 12:1 compression and 256/266 cam, although it does have L88 heads. The Hemi is fine on it too.

AR67GTX said:

I’ve been using 91 no-ethanol in my old cars for a couple of years now

Click to expand...

Agreed. The bigger factor for me is non-ethanol. I too have been using the 91 n-a, but have been adding an octane boost from VP Racing. The 340 may not actually need it, but the stroker I'm building probably will.

Have you tried DIY grade mixing at the pump, being its likely slightly cheaper and you can better dial in the octane your set-up needs?
An upgrade your combo is very ready for if not already reached, is almost any EFI set-up that includes timing control, a knock sensor and fuel sensor IMO.

You should do a cylinder pressure check to see what it is. This is always good info to have when paired-up with your fuel quality needs.

You still need to kinda monitor the situation.
I was able to run mid grade on my 383 for about 5 years after I rebuilt it.
Hypereutectic pistions, heavily milled 906 heads with 9.4 : 1.
But after some carbon built up over a few years it started pinging.
I backed off the timing but ended up going to "premium" at the time 93/94 octance.
That combo only had 145 - 150 psi but probably no the best quench setup with a cut down open port head.

and yet another reason to drive her across the country

I have about 160 pounds of pressure in my 318, so I use 89 octane. Had to put 89 in my bike a week ago, and it ran quite sluggish, and sounded bad. Back with 91 and Bluzu is happy again. I think compression is about 10.5. Fuel injected.

Some detonation is a silent killer, it'll destroy your engine without ever hearing it. Pulling race cars all across the southeast 30 years ago with my 440 equipped dually taught me that. It was 8.5:1 and it sounded good even on 87, but after a 300 mile pull it sucked the valves through the seats from silent detonation on stock 1978 truck heads. After that I installed an MSD Electronic Knock Alert system which lights up at different stages of detonation, MSD timing controller, a Holley mile-dial system so I could richen and lean the mixture at will, and a methanol injection pump for quenching severe detonation. It could run on 87 but you had to back up the timing, fatten the mixture to the max and squirt alcohol on hills, absolutely no fuel mileage on most regular gas. It also taught me how inconsistent gasoline quality is. Some tanks of 87 knocked less than 93, and some premium knocked worse than regular. It's a shame they don't make EKA or mile-dial anymore.

Kern Dog said:

For over 23 years, I've been a slave to the high cost of Premium fuel when I buy gas for this car...

View attachment 1886350

The first 440 was built and swapped in the summer of 2001. It was iron headed and around 9.2 to 1. I ran Premium 92 then...

View attachment 1886352

When the octane dropped to 91, I don't know if I noticed a difference. I built another 440 in 2004, this one with 9.5 compression and aluminum heads but still ran Premium 91. That mill threw a rod at around 850 miles so I got another 440 block and got a 4.15" stroke assembly to get 493 cubes. I was now at 10.8 to 1 and still needed Premium fuel.
Over the years I've dealt with detonation. I've tried delaying spark advance, limiting the advance, making sure I wasn't running lean, bigger cam, thicker head gaskets, higher octane fuel like so:

View attachment 1886353

In 2022, I pulled the engine to go through it after a camshaft went bad and ate several lifters. I took this opportunity to lower the compression a bit but add quench.
I'm now at 9.8 to 1 but I have a quench distance of .040. I've been careful and have kept using 91 octane fuel at every stop...until May of this year.
On the way home from a car show weekend in Van Nuys, the group I was with stopped for gas just off the freeway. Just for the heck of it, I topped off with 89 octane mid grade.
Now, I still run 35 degrees of total timing which is in around 2500 rpms. The engine did not knock at any time but just to make sure, the next fill up I tried 89 octane again.
Still no knock and no run on when I shut it down. It has me wondering if I could actually run it on 89 octane.
I've been careful to always run the highest grade gas for years so being able to get away with cheaper fuel in the lower octane is great! I don't mind paying for the better gas in this car since the car is not a daily driver.
Still, if I can save 20 cents a gallon, that is cool. Also, it is nice to feel okay if I stop at a gas station that only has 87 and 89 octane.
What is the highest compression ratio that you have ran on regular or mid grade gasoline?

Click to expand...

Geoff 2 said:

You could hear det with your engine using a particular fuel. So you know & can hear it [ hearing still good ]? If do not hear det now with a cheaper fuel, go for it.....
I have seen tests where higher octane fuel made less HP than a lower octane fuel, so no point spending extra $$ if it does nothing...

Click to expand...

The higher the octane, the more resistant the fuel is to burning. 87 octane gas dos have more energy in it, so the lower the octane you can safely run, the better. Of course, detonation can be a very bad thing...

PlymouthMakesIt said:

... installed an MSD Electronic Knock Alert system which lights up at different stages of detonation...

Click to expand...

This is a great idea. I might need to buy me one of those!

"The higher the octane, the more resistant the fuel is to burning."
That is a mistaken characterization
Technically, the real issue concerns the tendency towards self-ignition/pre ignition, not resistant to burning.

Your valid comment on lower octane often having higher energy deserves an explanation. Energy when defined by the gallon, and has its octane altered/increased by another additive, displaces a certain amount of low octane fuel that makes up the original gallon, and that octane booster seldom has more energy per volume than the amount of low octane fuel it displaced, resulting in slightly lower energy fuel per gallon with a higher octane.

I guess I've been lucky. I'm able to run 88 clear gas through my 440, aluminum headed engine with a decent sized cam and about 10.25:1 cr. Quench is around .044"

Heck, maybe I could run the 87. I have not tried.
I too have read that the anti-knock compounds that make up "octane" do factor in with energy density, in other words, 87 octane has more energy density than 91. It may not mean much overall, I've never looked that deep into it.
It just impressed me that I could run a cheaper, lower octane fuel than I have in the past. It gives me some relief knowing that I'm not in a jam if the 91 isn't available when out on the road.

All this talk of Electronic Knock Alert and mile-dial devices... too complicated for this dumb Appalachian hilljack. Since I'm not towing anything, and I'm not looking to pull 9-second passes, I'll just stick to non-ethanol fuels, and enjoy my cars. But for those in need, I hope all these solutions work.

Modern Car. While back East with more sane gas prices, I’ve been using 93 Sunoco and an occasional 94 treat. Mileage seems to have improved and it seems happy. Hellcat.