99-LS1-SS

I just heard from a reputable tuner that running 100 octane gas in a non-spraying stock motor instead of 93 octane can slow your car down some. Can someone explain how this happens. I guess I need to know what the purpose of different octane levels is and how it relates to horsepower.

Jake99SS

Higher octane reduces gasoline's tendency to pre-ignite. 100 octane gas will burn slower than 93. You only need to run enough octane to keep the engine from pinging.

99-LS1-SS

I guess the pre-igniting is what makes the pinging sound. If so thanks for the help.

STRIPSTAR

iTrader: (4)

yeah, knocking is gas burning before the spark. If your motor doesn't need the higher octane it may slow it a tad because the higher octane gas burns slower.

samz28

you can run more timing with higher octane.

Also on hot hot heatsoaked track events, you might not detonate at all on the goody gas.

only problem is if the motor adjusts to the new timing settings, and you wash the tank empty back to 93 it might knock a bit till it learns. Best to mix it back down.

If you have a programmer i spose you could change your high octane maps a little more aggressive once the 100 octane is fully mixed in. Those with higher than stock compression would benefit even more. (likewise boost-heads would too).

These ecu's are designed to push the limits on timing and knock, and learn the best situation (hence the interpolation of the high/low octane map). Thats why the motor can extract every last drop of power. If your next fillup sucks (pissed on gas) your motor will start moving towards the low octane maps.

With efilive 6.3 i think you can actually log where your motor stands on the high/low octane byte. Things like oil consumption (pcv,blowby,etc) can move your value lower.

in an ideal world with a perfect motor and perfect temps you'd be 100% on high octane maps with a stock motor , but we don't drive in ideal conditions most of the time.

I'd add some 100 octane and then 93 octane , then drive to the track if its was like 95F outside for added protection from detonation and maximum power.

JZ'sTA

iTrader: (23)

I have seen on a dyno a guy make 271 on 93 octane.
He had about 1/8 tank of gas.
He pulled the car off the dyno and added 13.xx gallons of 100 octane.
The gas station was about 10 miles away so the computer had some time to relearn.
He picked up 2 RWHP on the dyno 1 hour later in 85 degree weather.
Noo other car had been on the dyno after his and nothing had changed.
They were simply testing the power difference between the different fuel's.
For 50$+ per fill up I will stick with 93 unless it is really really hot.
(I do live in florida)

samz28

do the same but have him reprogram the car to add more timing across the board... I'd bet if you pushed in the max possible timing through edit you'd find a little more torque.

For me i'd rather just not detonate -heatsoaked staging and lose a 1/10th because the car is pulling back.

That might be worth a gallon of toluene an extra 1-2 octane is a small price to pay for knowing the car isn't gonna detonate going down the 1/4 mile.

Pro Stock John

iTrader: (34)

A DOZEN WAYS TO PREVENT DETONATION

1. Try a higher octane fuel. The octane rating of a given grade of gasoline is a measure of its detonation resistance. The higher the octane number, the better able the fuel is to resist detonation. Most engines in good condition will run fine on regular grade 87 octane fuel. But engines with high compression ratios (over 9:1), turbochargers, superchargers, or with accumulated carbon deposits in the combustion chamber may require 89 or higher octane fuel. How a vehicle is used can also affect its octane requirements. If a vehicle is used for towing or some other application where the engine is forced to work hard under load, a higher octane fuel may be necessary to prevent detonation.

From:
http://www.federal-mogul.com/cda/con...3_7525,00.html

Now, if you have a stock compression 10:1 LS1 and as stock longblock I would not use 100 and I would not mess with trying to max out timing on 100 unless you are in some sort of racing class.

I have seen folks run as much as 31/32 degrees on stock compression with just a cam.

I have seen folks run as much as 36 degrees of timing on 110 leaded with a cam.

samz28

wheres the other 11? http://www.elektro.com/~audi/audi/toluene.html

TheMongoose

if you don't(read can't) adjust the timing then there is no benefit. the big numbers come in advancing the timing. that's why you track knock retard. simple equation. if you can get the 100 then do it. just use edit or something to set the spark adv.

99-LS1-SS

I don't have any knocking. I was under the impression that 100 octane helped make more power. I see now that I was misinformed. I really appreciate the octane lesson. This is something that I really needed to know.
It makes since to me. I went to the track and filled up with 100 octane when I got to the track. My best time was my first time. Each time got just a little bit worse. Not much but enough to notice. I guess it was the gas.

jhillyer

Ooooh, please, careful there. We don't want people to directly relate octane to any difference in rate of burn. Correct, about pre-ignition. I would wager, however, that as octane is increased, and compression-ratio and spark timing remains the same, increasing cylinder+head temperature would help maintain ignition timing, so warm-up. Otherwise, advance ignition and/or increase compression.

McRat

I tested 91 octane and 100 Union 76 Unleaded race gas on the same day, same dyno, same car. 2000 Camaro SS, 3 pulls on 91, drove to Union 76, put 100 octane in (about 80% mixture), drove back to the dyno, tied down again for 3 pulls.

Verdict? It eliminated the 1-2 deg KR that the car was getting on the dyno, but no significant gain in HP (or loss). Maybe 2 hp gain in certain areas.

383LQ4SS

iTrader: (33)

I think if you retune for the 100 you wont see much of a loss.

If you were running 93 and seeing knock resulting in HP loss...you MAY pickup a few HP depending on how bad the knock was. But that means your tune was incorrect for the 93. (assuming the knock was not mechanical related or false knock)

I believe...if you have 0 knock on 93...add 100 octane to the tank...do no tuning...you will probably lose a few hp.

Everytime I went from 93 to 100 octane for the spray runs...the car would run very rich. I usually had to lean it back out 3-5%.

I did try to retune and add more timing using the 100 octane...but it did not get me any more HP over the timing I had set for the 93.

Ryan04Silverado

I got a question then, is it possible for the motor to run better with 89??? Just curious.

McRat

Yes. If you've got 9.0:1 compression.

Keep in mind though that some race gasolines are oxygenated. You can burn more fuel per cycle than "normal" gasoline. Not a big gain, but a gain. You must tune the engine richer to get the gain.

The Guy in MY 99TA

it really should but to run the 89 octane the compression is a little high and the timing would have to be really low....... but it would RUN off of it but with the timing requirements it really wouldn't be effective.

I love it when people say"hey put some 93 octane in her and she'll run like a raped ape!" and then I have to give them whole octane rating deal. Its funny as hell. But its all in the volitility of the fuel(octane rating) higher octane burns slower than lower octane ratings so the lower the quicker it burns which would be more beneficial BUT it just doesn't work that easily in higher compression engines.

Josh S.

dazman

in a 2000 z28 M6 with NO mods but a borla (no plate) i made 320 rwhp on 87 octane... 75 degrees outside... after i put the cam in and it got hot during the summer the 87 would detonate like a *****, so started running 93 for summer time.

mike

dazman

omg man.... these *** clowns down here LIVE by that crap.... they are like," wow i got 150 hp with 115 octane true blue baby!!!!!!!!!!! lol

lmao

mike

WS6 RULES

I used to work for Union 76. We tested different fuels in test engines. The reason high octane fuel burns slower is to produce more power. You want to push the piston down not knock it down with a shock wave. And that is what knock is. On low octane the spark plug fires and the fast burning fuel sends a shock wave to the piston which is still on it's way up. So then the wave bounces back up and hits the head. That is the knock you hear, and so do the KR sensors. On high octane with the proper timing the plug fires and the fuel begins it's slow explosion as the piston is still on it's way up. By the time it reaches TDC and begins to go down a nice long push forces it down. And that is what makes high octane produce more horsepower. Why do you think those blown top fuelers at the drags have that long flame coming out the pipes? The fuel is still burning, super high octane. That slow burning fuel is pushing that piston all the way to the bottom.