TurboTommy

Yes Todd, you are right.
I don't understand, either, that people are feeling more power just by going to race gas. You'd think there was something wrong with the car then.
I think it's just a natural human emotion: "it must be faster now with this super fuel"

Posters, here, should give concrete examples and communicate their observations to illustrate exactly why the car is faster.

eclou

You are looking at it from the wrong direction. The computer will actively pull back on the timing when it senses knock or pinging. On our modded cars we are probably pushing the limits on street fuel. The addition of some race gas may allow the motor to run at full capacity. That's why some people try to data log info from the knock sensors - to see how close to the edge they are getting.

TurboTommy

Yea, eclou
so you're saying, then, that the computer is quite often pulling back timing. Yea, I know; and then you'd constantly feel stumbling/hesitation. I'd consider that as something being wrong with your car prior to running the race gas. Of course, then the race gas is gonna make you faster.

B951S

Agree, I don't think the DME will advance to 'find' a knock limit for a given fuel. The timing curve on a given chip is based on a certain fuel octance. Danno, please chime in with an explanation as we would love to hear your thoughts on this.....

jsonnen

But if the DME can sense knock and retard the timing due to low octane then it must be able to give back what it retards? Doesn't that make sense?

eclou

Why would there be knock sensors in our motors if the DME didn't use them for something?

NeedPorscheSpeed

I just got in from "exercising" my S2 and 968. Even though they are my "boostless" Porsches, they still induce a million smiles per mile! Like you, I love these cars!!! Long live Porsche!

MildMax951

I'd like to add some practical experience. Where I live pump fuel is 88 octane (by USA standards, ie it is 93 RON). When I first got the car and was only running 0.9 bar boost with an LBE and no chip modification increasing the octane gave positive results.

I initially used "Witches Brew" a mix of toluene, xylene and ethanol sold by a local Subaru tuner. Without the octane boost the car just felt gutless particularly on hot days. This was backed up by dyno runs with and without octane boosting. You could see the torque drop off on the chart when knock occurred but you could never feel it as a single event while driving, there was no stumbling or hesitation the car just feels lazy.

As to what the DME does, it backs off timing in two steps of 3 degrees when it detects knock, when knock is no longer detected it puts the timing back at 0.3
degrees per 100 ignition pulses, but it never exceeds the ignition value programmed into the chip map.

I am agreeing with TurboTommy and others, if your particular setup is short of octane relative to fuel you're using then increasing it will help, if not then you're wasting money. Remember I was only able to see positive results because the available pump fuel is of very poor quality.

azmi951

A reduction in timing will not feel noticibly bad. when knock is detected it feels seamless, your car will just feel lazy. I loved the way my car felt in Michigan with cold air and 94 octaine vs the Arizona heat and that 10% ethanol overpriced **** gas.

Somewhere I also saw that our cars have a fuel grade sensor built into the KLR. Anyone know about these?

Speeking of bad/cheap fuel how and/or why are somestates not allowed the good gas like 94 or 93? like Arizona? Can we send a letter to our congressmen or representitive?

toddk911

"Agree, I don't think the DME will advance to 'find' a knock limit for a given fuel."

Wouldn't that be nice!!! I think that is the purpose of VTEC motors and/or variable timing like the 996's Variocam system.

"Why would there be knock sensors in our motors if the DME didn't use them for something?"

Stricly safety. Knock is detected, timing is pulled back, not advanced if high octane is run.

But as stated earlier...Danno????

I know some Shell stations have 94 octane. Ar least the one up north where I grew up did. The you have the Sunoco GT100 fuel at very few locations. But as stated and proved in another current thread (water injection) much more benifit to performance to run WI as opposed to race gas andin the long run much cheaper, with gas so expensive and Xylene/Toulene about 10$ a gallon. Although I agree much easier to pop into Home Depot or Sherwin Williams and pick up a quick gallon and pour her in

Would there be any benifits to adding methanal straight to the gas tank??? Like 10-15% mix?? As it is so cheap, at least iof yo ucan run the methanol base washer fluid like what is run in water/methanol injection systems.

M758

Octane does not equal power.

If you car is knocking then yes more octane will restore the power the car should have. Honestly if you running "on the knock sensor" with timing be constantly retared you need to remap to the fuel level you have locally. The knock sensor timing retard is not a feature to be used, but really self protection mode for the car. Mostly it means that one tank of bad gas will not hurt the motor. That of course does not mean you should run all the time with "bad gas".

I put 110 octane leaded race gas in my 944 na once. I did nothing except lighten my wallet and turedn the inside of my exhaust pipe white. No power gain, nothing at all. So I just stick with 91 oct pump gas in that car. Stock those cars were mapped for 87 oct gas. I run 91 since it is very cheap and the extra stress of racing especially in the heat could cause a knock. Since that motor does not have knock sensor why risk engine damage for 20 cents a gallon?

toddk911

Here:

http://www.goemerchant7.com/index.cgi?PageToView=catalog&Department=81048&Cartid=21641090955886&Merc hant=highfuelsn&ExpandedDepts=81048|

toddk911

Holy crap!! They sell Nitromethane!!

flyguy

dont bother with methanol. it evaporates so quickly that unless your gas tank was COMPLETELY sealed, it would be gone within the hour... probably less. I use methanol in the lab as a carrier fluid, and if the stuff spills, a small puddle will evaporate in a few minutes.

rage2

Good post! Also note that higher octane fuels has less energy. So if your car doesn't knock on 87, and you use 91 octane, it'll make less power, and have poorer fuel economy, because it's not taking advantage of it by advancing timing.

Of course, the oil company's marketing department don't tell us that heh.