Bill S.

I've been using 100 octane (R+M/2) in the CGT for a few weeks now. After a few days, I noticed the throttle response became much faster and the acceleration noticeably stronger when compared to using 91. It seemed to take a few days for the car to adjust to the higher octane, but now it's like a different car.

Has anyone else noticed this?

JChoice

I'm going to try this out but was going to mix in the 100 and 91 so that I get about a 95. It's cheaper than going all 100 and I believe the manual states the car was made for 94 octane.

bbs993tt

Would like to try that given your positive results. I have no idea where you can get 100 octane fuel around here though. Is it readily available near you?

Macster

The change in octane may be the cause of the difference you notice. OTOH, beyond 93/94 octane the engine can't take advantage of the higher octane. (However, over time and engine's octane requirements can go up by several points but generally this occurs from usage/wear and unless you've put alot of miles on your car chances are the engine's octane requirements are unchanged.)

Another possibility is you are pushing the car harder and the engine controller is learning more agressive fueling/tiiming and you are noticing this.

Yet another possibiilty is the temperature/humidty in your area have changed and for the better regarding engine likes.

And lastly, fresh fuel may play a role. A fuel test done in an Evo car mag (UK published) found differences measurable on the dyno and differences observed by a test drive between tanks of teh same brand of gasoline bought at different stations at different times. The freshness of the gasoline was the reason.

Premium gasoline goes stale pretty quick. If the car is filled up and then not used for a while even if the gas was fresh when the tank was filled up the gas can go stale. Any ethanol in the gas doesn't help as the fuel can stratify if allowed to sit too long.

Sincerely,

Macster.

rijowysock

engine cannot take advantage of the higher octane without being tuned specifically for that octane..

100 octane will not make the car faster, if anything will make it slower..

stick with what's recommended on the car. i think 93 Ron+Mon/2 correct?

car's should actually be tuned for 91 octane in USA due to the fact cali is 91 max.. which means you could run half 93 and half 89 everywhere else for ideal results.

spare tire

I also put 100 in my GT3 and I think it makes the trotttle responce better or quicker. It is not tuned for 100 so I am not getting more horsepower but the motor seems to like it a lot. I only drive it on the track and the butt dyno says there is an improvment. It is my belief that the timing will advance to the MAX by doing this. If you retard the timing on an engine it tends to have less power but the engine runs super smooth. The is what running 100 feels like. The engine runs noticeably smoother but no real gain in horsepower. I think it is a benifit and will continue doing it.

wtdoom

I eat the best organic foods . I stay away from junk and processed crap . My Cgt deserves the same no ?

Macster

The behavior you notice is not due to the 100 octane but is just a characteristic of the gasoline.

A fuel test some while back found while different brands of gasoline were tested and they all had the same octane rating there some pretty striking differences in how the engine performed and felt to a professional driver on a track.

Some gasolines were 'flat' a low rpms but had super mid-range then tapered off at the top. Some were ok at lower rpms then at hgher rpms just made the engine scream to redline.

100 octane overkill but I think it better to run that especially if you are tracking the car than some lower octane rated gasoline.

My info is Porsche uses a 94 octane gas to test its cars and they are tuned for this octane grade of gasoline. If fed a lower octane the engine controller can adapt by retarding timing.

This is not ideal (raises exhaust gas temps and the engine is less efficient) but better than the alternative (detonation!).

Keep in mind on the track under high torque demand (lots of throttle) the engine controller can and will go open loop and thus supply a richer air fuel mixture to the engine which not only improves the engine's output but lessens the chance of pre-detonation signals (from the knock sensors) causing the engine controller to retard timing. Also, under harder acceleration timing is usually retarded (less advanced) than it is at part throttle cruising. Under hard acceleration I've seen my Turbo's timing fall back to the mid-20s or so while under part throttle it can be advanced to the mid to high 30s (degrees).

But still 100 octane better (offers more a safety margin) than running 91 or soemthing less than 94 octane gas.

Sincerely,

Macster.

spare tire

And I forgot to mention that if you fill up with the stuff and put your car away for the winter then the fuel will not vaporize when it is cold so you cannot start the car. Some 10 - 20 degree cold days that are clear I like to exercise the horses. Not with 100 though.

toddk911

Do you have any more details on this analysis that was done? Which brands faired better than others, etc. ?

Macster

I have the Evo article in PDF format. It is for UK gasolines though, but you are welcome to a copy.

It shows that various gasolines deliver varied experiences.

Send me a PM with your email address and I'll respond with the PDF.

If you want I can include a 3 part article on PCCBs from Total 911.

Sincerely,

Macster.