Reg 87-Midgrade 89 or Premium 91

I have a 351C 2V with plenty miles..wondering what octane is best ?? I can't tell much difference in the grades, just maybe trying to save a buck or 2..

 

If your car is happy on the cheap stuff, use it. The high octane has no more energy in it than the low octane, it just burns slower thus helping to prevent preignition.

 

what he said. Actually too high of octane will expel unburned fuel into the exhaust, thus shorting you of power and mileage. Although to get that effect I think you'd have to be dumping bottles and bottles of octane booster into premium. If you're not pinging on the cheap stuff keep using it.

 

I've always used premium. My ol skool thought was that the higher octane resulted in hotter spark and better mileage, but at prices today WOW.
Curious what you guys/gals run in your 'cheros..???

 

strictly goat pee..."The Rock" doesnt seem to care with his lopo motor

 

What if you're 'Chero spends most of it's time parked? I don't drive mine very often so when I do have to put gas in it (every six weeks or so) I generally use premium with the thought that as gasoline ages it looses octane so if it starts-out as 91, weeks later as it sits in the tank it's slowly degrading to 87. Or am I just wasting my $$? Mine also seems to run fine on just about anything I pump into the tank.

Kevin

 

I think this can be a useful and interesting thread (seriously)

...NOW...where can I get summa that GOAT PEE

 

I have run both 87 and 91 in my Chero and Torino (engine swap). I seem to get better gas mileage with the 91 vs 87. Then I do use my Torino for a daily driver. Also the engine seems to run smother with 91.

 

With the older engines I always have found I get better gas mileage with the higher octane...that being said I don't know if that offsets the higher price at the pump. I understand all the gas nowadays is better than the gas from the past, whether they mean it is cleaner burning or what I am not sure. My new mustang demanded high octane once I had chipped it...and it ran great with the high octane. I could reset it to use the lower octane but preferred the extra performance etc it gave me. My 'chero will run on low octane but I usually use the mid-grade as I don't run it all the time so figure the gas will stay better longer than the low octane...if I am going on a longer trip I usually will run the expensive stuff for a couple of tanks to clean up the combustion chambers then run mid-grade. Maybe I am wasting my money...but then again maybe not!!!!

 

I usually put 91 alcohol in mine which is 20 cents higher then 87.
One of these days I am going to try non-acohol, 91 or 93. Which of course even higher in price. Hell whats another $6.00.
Non alcohol gas I hear gets better gas milage.
Again I do not know if the price difference will be worth it.

 

I started the thread after running a few hits of 87.. wasn't too sure if I could tell a seat of the pants diff..switched back today to 91 and I did seem to get further with the same gallon amount of 91. The power feels better too with the higher octane stuff.
I notice especially on the highway that I don't need as much pedal to sustain hwy speeds. That being said, I could be nuts, i guess that's why they invented placebos..now about that Goat Pee....

 

See Achmed about the goat pee, or Ahab.
The 'fruit of the loom dyno' is not worth considering. Write down your milage and the amount of gas used, and compare.
Don't discount the 'sucker' factor either. Doesn't a car feel faster after putting on $600 wheels? Of course it does. I am sure that if you put $6 a gallon race fuel in it it would run like a NASCAR rig.

 

Hell I know what you mean..I washed Ol' 'Foam the other day and I SWEAR it ran better..

 

My 77 has a 70 Windsor in it. I had a ping with low and mid-grade. Went to hi-test and the ping went away. After about 6 months the gas mileage improved from 11 to 13.5 mpg. Gonna try regular pure gas and see how that goes. I hate ethynol.

 

That's weight reduction! Get rid of enough dirt and you're good to go, lol!

 

I am able to de-tune my "302" (bored, re-worked heads with a Edelbrock RPM Performer intake and cam, Pertronix Flamethrower & Hedman headers) so that it runs on low octane. It gets decent mileage (average mid 20's ) mostly around town and with some highway. That said, if I want it to run really well (for the occasional drag race) I advance my timing, change the metering rods, open the secondaries sooner on my Edelbrock AVS and put in premium.

If you don't change the way your engine is tuned and are getting by on low octane (ie. no pinging under load) I see no reason you should spend more on higher octane. However, if your Ranchero is as loud as mine, you really need to check your spark plugs to see if you are running OK with regular. I can not not hear my engine pinging because my Dynaflows are pretty much straight through and come out just behind the rear wheels. I easily set off car alarms when I drive through a parking garage. When I first ran it I had 3 inch pipes that dumped just in front of the axle. Then the alarms went off just driving down the street. I was louder than a pack of Harleys and there was no possible way I could hear my engine knocking. I had to pull the plugs to see if my timing was off when I wanted to run on cheap gas.

 

Find a friend who is well versed in chemistry. More octane on the benzene ring means more oxygen, and therefore more energy when those bonds are broken through combustion. Yes, it takes longer to break those bonds, and that is benificial to pre-ignition. That said, in good old show me land of Missouri, you can't buy any grade of gas without at least 10% ethanol. The difference is in the octane rating, and the amount of additives (detergent, if you will) that keep the valves clean. Years ago, when gas was sub $2.00 and the mark-up was 10 cents between grades, you might quibble over the cost difference and effect. As the cost of gas gets higher, the premium paid for the higher grades gets less and less significant. If you tear down your engine on a regular basis as a matter of course, then go ahead and use the cheap stuff.

 

I guess I am fortunate...(???) to live in a town with a Marathon Oil refinery.
Talking to a couple of Chemical engineers about this, they recommend that for anything built prior to 1986, you run mid-grade or premium. (locally there is a $0.22 difference from 87 to 91 octane )
All 3 of them said it is because it burns slower, has more detergent in it to keep fuel injectors clean (And the inside of your carb....) and that cars built back then were actually DESIGNED to run on 90 octane fuel because that was the octane rating for REGULAR gas at the time.
All I know is my chero likes 89 -90 octane...it runs ok on 87 but fuel mileage suffers at 15.3 open road. If I run 89 or mid grade I will run 18.5 after about the 3rd fill, since you still have a few gallons of older fuel in the tank when you fill it. Running 93, doesn't improve mileage, but driveability around town gets better after a tank of it..( probably cleans out gunk from the power valve or something....)
So now I just run 89 all the time. When I go to a show 1-2 hours away I'll throw in a tank of 93, just to clean out the gunk...cheaper than fuel system cleaner!
So that is my $.02 on this topic.... The best way is to try a few tanks at each level of fuel, WRITE down your mileage as suggested before, and figure out what your beast likes and doesn't like! But I figured that for $3.10 extra a fillup...that isn't really too bad a deal for a nice running car.