this post doesn't really belong on any specific board so i'll just put it here. my question is: what's the advantage of using higher octane fuel? i was lookin up supra TT's on ebay, just cause anything with TT is badass. on somebody's auction they said the car was dynoed with different ocatane gas. with 91 octane the car had 521hp and with 118 octane it had 595. i know that i wouldn't use 118 octane gas, and with a car that only pumps out 140hp, the gain (if any) wouldn't be very much, but what's the advantage of going with a higher grade? i use the cheapest gas just cause it saves me $1.50 a tank, but would it be worth a switch?

 

Different octane gas just burns slower or faster. The higher the octane, the slower it burns. Octane is used in high compression engines and in engines with a lot of timing because it resists the spontaneous combustion that causes pre-ignition/detonation. You actually get more power out of lower octane gas because it burns faster creating a bigger bang, but if you run a lot of timing or have high compression, you get knocking with 87 gas.

That's the reason why the Corvettes have to run 91 octane, because they have 10.5:1 compression, but with our silly little 8.5:1 compression (or is it 8.1:1, can't remember), we'll get the best power out of 87 for everyday driving. If you want to add a lot of timing for a day at the track or something to squeeze out that extra 0.1 of a second, put some 91 in there and set the timing.

I think the guy who is selling the supra is BS-ing, but it's possible that he did dyno it with the different grades of gas. If he has a custom chip, he could have programmed more timing into the car and ran it with the 118 octane with A LOT of timing and got more power that way. And then when he ran the 91 octane the egine started to knock from all the advance so the computer retarded the timing, resulting in less power. Possible, but highly unlikely.

Plus, what the hell else did he do to the car to make it have that much power. There is no way in hell a Supra TT came with that much power from the factory, or could even get that high with just the normal "import-tuning" crap.

All in all, this is what i think of it...

 

oh ok, thanks for clearing that up...about the car on ebay, supposedly there is $70K invested in the car, with the biggest thing being an intercooler. he has a huge list of all the upgrades, so i don't doubt that the car is putting out 500+ hp, but after reading your post, yeah i bet he messed with the car alot to make the results so different

 

???.......

High Octance fuel ignites a higher combustion force at a cooler combustion temp than lower octane fuel. The lower combustion temp in the cylinder allwos for lower head temps thus a denser fuel charge as well. Yes it does make more power. A higher performace engine will show more of a result than a stock motor. I run Aviation fuel in my Vette with a highly modified 327 smallblock that puts out 540RWHP on pump gas and believe me you deffinately notice a difference bigtime ( this motor twists 8500rpm's and has a combined advance of 40* at that rpm).

 

2_point8_boy is 100% correct, all ocatan does is prevent pre-ignition/detonation. More power and better MPG are pipe dreams.

 

ok, here's clarifiacation for that. Out of a lower compression motor, you get more power out of lower octane gas because the combustion is more instantaneous(sp?). The more compression or timing you run in the car the higher octane you need to keep the engine from knock, and although the higher octane burns slower, the added compression/timing more than compensates for the less than "instant" burn time.

hope that makes me look like less of an idiot...

and wooohoooo!!!!! This proves it....that I'm not just sharp as a marble afterall that is.

 

Also, on a mostly stock motor like our 2.8's and 3.1's, we aren't running a total of 40* advance. The computer has a set amount of timing, and unless you go in and change that by getting a custom PROM and by twisting the distributor A LOT, you will NEVER see a performance increase on our motors.

 

The way you have to think of octane is a graph.

87 Octane is not linear at all, its combustion is very random which makes it a lower grade of fuel. Many cars are designed around this randomness so we can pump cheap fuel into our vehicles.

92 Octane is more linear, it has a more percise point where it will always detinate. Therefore giving high performance engines less chance to knock.

As far as pipe dreams on Supreme VS regular, that is still a debate. I know that is what GM and FORD etc. says to run. But thats the minimum fuel you can run, running the minimum does not always mean its the best for your car. I know I got better milage with 92 octane then I did with 87. As for power I did not notice a big difference. But I recommend running whatever you feel your car runs on best.

 

o.k. guys- you are mainly correct except for the quote I corrected above
quote:
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Originally posted by 2_point8_boy
You actually get more power out of lower octane gas because it burns faster creating a bigger bang
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This part is not correct.
On a stock motor with stock timing advance (10* on ours) there is no increase or decrease of power running a higher octane fuel. One burns faster and hotter (hotter is not better) and the other burns cooler and more complete.

Now you take your stock motor and increase the timing to 14*(like so many of us have) and run 87* octane, you will predetonate and rob power plus hurt your motor. Use a higher octane fuel and you can run that 4* advance and more cleanly and effectively utilize that higher octane fuel to combust sooner and burn slower/cooler and more complete as the piston reaches the top of the compression stroke- creating more power and better fuel economy.

Higher octane fuel will produce more power in any engine as long as you increase the ingnition advance to its potential.

Also as I pointed out above- It burns a more thourough/powerful combustion at a lower explosive temperature. Heat is not power- in fact the opposite, heat robs power- How can this be true?- The head and cylinder temps remain lower and allow for a denser charge of fuel that contiually combusts at a lower temp. ( 2 Things cause pre detonation of low octane fuel - 1{raised compression, and 2{ hotter cylinder temp)

87- burns quick and small, not complete
91 increasing to 118 -burns slower but builds force higher with a more controled complete burn and need to be ignited sooner for a noticable differnce.

 

actually 2.8 boy our engines have whopping 8.9:1 compression ratio. Just in case you wanted to know the actual amount.

 

Here's the clincher- on a higher compression engine the high octane fuel becomes more likely to pre-detonate so of course it needs to be used- but the reason for even higher octane racing fuels ( 100 t0 118 octane) is mainly for very high RPM motors- like my 327 in my Vette that turns as I stated 8500 rpms. Pump gas will run fine with the same power output until roughly 6000 to 6500 on my motor- but because of compression an velocity, the pump gas will start to pre-detonate sometimes on pump gas above these rpm's so I run AV-gas to properly attain these high rpms safely where this motor does produce more power.

 

bes217 says 8.5 to 1 in the GM manual.

AGood2.8 it cause Aviation fuel has a higher btu value per volume then gasoline not because of octane.

 

To finally answer the question: It wouldn't be worth it to waste the extra $1.50/tank everytime you fill up. Remember, that's a PERSONAL OPINION and is not meant to **** anyone off, seeing as that i have started a very volitile :sillylol: topic with my statements.

 

No, everybody is just stating their opinion which is what this group is about.

 

was supposed to be funny, good thing I'm not in comedy, huh?

 

Just to point out on the Supra guy - he is NOT BS'ing anything.

Higher octane prevents detonation. On a twin turbo, guess what that means? More boost. More boost = more power. 118 Octane vs 91 octane should provide like 4-6lbs more boost capability.

NO 'import-tuning' bs there.

/rant

 

right, but I didn't know that the guy had almost 70K invested in the car. I was just saying that if he had just the usual imprt junk on there, there is now way in hell he would be pushing those kinds of numbers.

I never have a problem clarifying or admiting that I was wrong, and in the case of his upgrades and statements, I was wrong, but i answered the question as best I knew how.

Good Times

 

2_point8_boy, your not wrong, the extra power is not coming from the octane but from what the octane prevents in the form of damage and hp loss.

 

this is about the reply talking about advancing the timing from 10* to 14* if you're going to be using higher octance fuel....umm, how do you do this? sorry if this seems like a stupid question, but i've never messed with the electronics of my car so i'm in the dark here. i've seen on tv where they hook the car up to a computer and run a program where they can change all kind of stuff to increase performance..is this what you have to do?

 

no, for us you don't have to do all that stuff. It's the right way to do it, but they are using expensive PROM burning stuff and custom chips. All we have to do is twist the distributor. See the post in this forum about setting timing. It explains it all. This isn't the right way to do it, because once you have to go get emmisions checked, you have to twist it back down to 10, but it works for the rest of the 2 years so you don't have to worry much about it.