What octane level to use?

[BLLDOGG]

Originally posted by V8 Killer:
87 is what GM recommends.

89 and up is simply a waste of money...

do we have to metion why the mechanical engineers at GM get payed so much.

if you tune your car for 93octane, ofcourse it will run like *** on 87. just like if you tune for a bigger injector and have a stock one, it will probably run like ***. must i go on?

[oil pan 4]

I was wasting money with 87. I found it cheaper to run 91.
I must be waseing a lot of money saving over 1 cent per mile compaired to runing 87(even after factoring in 91 cost 20 cents more a gallon).
I was pushing 28-29 mpg on a rich running 5.0L Z28 with an auto trans.
That was before I tuned it up a lot and got it running realy good. I can burn the tires through 2nd gear all day now and bark 3rd real hard, when before it was strugeling to spin through 2nd.
It will be different for different cars.
Test it, don't let some one else tell you how your car will run.
All those GM engeneers were no where to be found when I figured out that my car was cheaper go miles powered by 91 (that was before I tuned it up too).
I did have to figure MPG but that didn't matter all I cared about was the $$$ I saved. After I started useing 91 it was very clear I was getting better gas milage but all I wanted to know was it cheaper to run 91???
I have a new LG4 runing 9.5:1+ (heads were milled a little and block was bored .01'' or .02'' when it was rebuilt) I run a couple of extra degrees of advance over stock at a not even near Stoichiometric A/F (need to play with the carb more) on my edelbrock 650 carb.
I spent a long time working on the Z when I was home this summer(so it could sit for a nother year and 1/2).
The only way to know for sure if it is cheaper to run your car off 91 then 87 is make sure you car is tuned up and figure you gas milage as close as you can then switch to 91 and then figure if it is cheaper to run 91.
Make sure the weather dosen't change a lot and that none of your tires get low and keep an eye out for little stuff like that.
Most you could be out is $6 or $8 after the few fill ups it will take to nail down the MPG on 91 and figure if you are runing 91 cheaper then 87. If you do end up like me and find it is cheaper to run 91 then you could be saving your self about 1 cent per mile or more.
Just think 1 cent times how ever many miles you run a year. Or even a half cent.
For me it is 1.4 cent's times how ever many miles I run a year. Yea it ads up fast.
So every oil change (5000miles with M1) I save $70 runing 91 compaired to runing 87.
I think I will keep wasing my money on the 20 cent more a gallon 91 and blow that $70 I save every 5000 miles on some thing else. I guess I would be waseing it if I went out and bought a new tool or some thing with that money insted of put it in the bank.

[oil pan 4]

Originally posted by 98Camaro3.8:
Lightly modded, untuned car: 87. Period.

True only about 99% of the time [img]graemlins/naughty.gif[/img]

[38fury]

Originally posted by oil pan 4:
I was wasting money with 87. I found it cheaper to run 91.
I must be waseing a lot of money saving over 1 cent per mile compaired to runing 87(even after factoring in 91 cost 20 cents more a gallon).
I was pushing 28-29 mpg on a rich running 5.0L Z28 with an auto trans.
That was before I tuned it up a lot and got it running realy good. I can burn the tires through 2nd gear all day now and bark 3rd real hard, when before it was strugeling to spin through 2nd.
It will be different for different cars.
Test it, don't let some one else tell you how your car will run.
All those GM engeneers were no where to be found when I figured out that my car was cheaper go miles powered by 91 (that was before I tuned it up too).
I did have to figure MPG but that didn't matter all I cared about was the $$$ I saved. After I started useing 91 it was very clear I was getting better gas milage but all I wanted to know was it cheaper to run 91???
I have a new LG4 runing 9.5:1+ (heads were milled a little and block was bored .01'' or .02'' when it was rebuilt) I run a couple of extra degrees of advance over stock at a not even near Stoichiometric A/F (need to play with the carb more) on my edelbrock 650 carb.
I spent a long time working on the Z when I was home this summer(so it could sit for a nother year and 1/2).
The only way to know for sure if it is cheaper to run your car off 91 then 87 is make sure you car is tuned up and figure you gas milage as close as you can then switch to 91 and then figure if it is cheaper to run 91.
Make sure the weather dosen't change a lot and that none of your tires get low and keep an eye out for little stuff like that.
Most you could be out is $6 or $8 after the few fill ups it will take to nail down the MPG on 91 and figure if you are runing 91 cheaper then 87. If you do end up like me and find it is cheaper to run 91 then you could be saving your self about 1 cent per mile or more.
Just think 1 cent times how ever many miles you run a year. Or even a half cent.
For me it is 1.4 cent's times how ever many miles I run a year. Yea it ads up fast.
So every oil change (5000miles with M1) I save $70 runing 91 compaired to runing 87.
I think I will keep wasing my money on the 20 cent more a gallon 91 and blow that $70 I save every 5000 miles on some thing else. I guess I would be waseing it if I went out and bought a new tool or some thing with that money insted of put it in the bank.

With your heads being milled that increased your compression, plus advancing your timing requires higher octane so you don't have detonation, in completely stock trim you wouldn't notice a difference between the two octane levels, just one costs 20cents more a gallon. Different strokes for different fokes.

[oil pan 4]

I found it was cheaper to run 91 before the big tune up, tuned it to run even better off 91. but the compression has all ways been a little higher sence I have had it.
It had 87 in it when I got it (or realy old nasty 91)and an stock tuning that was off a bit.
I kept the stock thermo that keeps the gauge at 220F all the time. I figure I might be running 9.7:1 at the most and that is a lot of octaine (detonation resistance/combustion delay) to over come with that c/r and I need the heat.
That reminds me, here is a loseing combo I see often:
Toss in a 160 thermo stat on a lightly moded car and start useing 91 :D .
Your car will run like a$$ for sure.

[Little G]

Originally posted by V8 Killer:
</font><blockquote>quote:</font><hr />Originally posted by Little G:
</font><blockquote>quote:</font><hr />Originally posted by V8 Killer:
87 is what GM recommends.

89 and up is simply a waste of money...

Not true: The PCM has a high and low octane table. The high octane table will yield more performance and better gas milage. A friend of mine has a new four-cylinder alero and it gets 50 more miles out of a tank of 93 versus 87. </font>[/QUOTE]So then whats the highest octane limitation?

If I dump in 120 Octane in my tank will I lift off? and get 4000 MPG? </font>[/QUOTE]Yeah, I like to use straight alcohol, myself. I fill up like once a year or something like that. It's great.


Seriously, though. Your PCM will adjust to a higher octane. But there are ONLY two spark tables, high and low. If 89 gets you into the high table, then 93 will only be marginally better, due to its better knock suppression. However, there is a limit. One time, I ran out of gas at the track and the lowest they had was 103, so I used it. The car just wouldn't make any power and the times did not improve.

So try different octanes and see what works best. If you see no improvement in mileage with the high octane, try the mid-grade.

[Riggs]

i use 93 consistently, recently switched over to it. better mileage too.

[BiH]

Originally posted by V8 Killer:
87 is what GM recommends.

89 and up is simply a waste of money...

I agree
it runs the same

[oil pan 4]

In Maine and Texas 89 octain gas is like 2 different fuels. In Texas it was good stuff, in Maine it is yellow (like P) same as the 87.
My car Z only has one spark table, the one I set.
If I could make my car run better and cheaper off 87 then I would, but it ain't happening.
Who here would buy 91 or 93 over 87 if it only got you 10 more miles per tank?
Or is it because you get better gas milage to the point where it is cheaper to run gas that cost more?
And with alcohol say methanol the octaine is around 118 but the BTU per gallon is about half that of gas. You have to run around a 6:1 A/F to run methanol, you have to burn about 2.3 time the amount of alcolol to make an engine run it like it is runing off gas.
Methanol engines like a c/r of 13.5:1 or more (up to 18:1 is the highest I have herd) and need a hot thermostat. alcohol burns very cool and it is hard to warm up those engines(the street engines).

[96firebird311]

I didn't read the whole thread, but unless you are hearing knock due to detonation, (usually those guys running turbo) 87 is more then fine. And I know this has been discussed several times. Please search. [img]smile.gif[/img]

[grayman]

Well, just keep track of mileage. fill up twice in a row with each type of gas. I have read in here many times...not counting moded and tuned cars...that stock engine people get different results from different fuels. It seems like some states/neighborhoods/gas station chains have different quality as well.

my testing showed no improvement while stock between 92/87. No loss or gain in performance either.

When I had the hypertech 93 octane powertune program running I did notice an improvement in performance...but that is a whole new topic.

[andrew.brandon]

did the same with mine and Shell 89 octane was the best for me.

[oil pan 4]

At least you tried.

[dorkins]

if higher octane isnt better, then why did i get 220 miles off of 13 gallons of 89, as opposed to 180 off the same amount of 87?

i have tested it more than 1 time... and same results...

[terminaldegree]

Originally posted by dorkins:
if higher octane isnt better, then why did i get 220 miles off of 13 gallons of 89, as opposed to 180 off the same amount of 87?

i have tested it more than 1 time... and same results...

That car is either highly modded or in terrible tune.

220 miles / 13 gallons = 17 mpg. Absolutely horrid!

I haven't been able to get mine under 21mpg, even with a tank w/ drag passes and mostly city driving in cold weather.

BTW, I run 87. Runs just fine.