smmmurf

I haven't tried high-test fuel in the GT4 yet. I have noticed smoother power delivery with a mix of 91 and 100 octane fuel in my 991.1S which has the same engine.

khooni

I also think some engines /dme are more prone to pulling timing than others. This could be the problem but Pete reports that he has found the same on 3 cars but sample size is still too small to definitively blame it on gt4's aversion to ca gas

stout

Agree sample size is way too small. However, 3 for 3 is hard to ignore, hence this thread.

Next step is definitely figuring a time to go visit my friends' chassis dyno with a couple of jugs of high test in tow. It'll be a while, though, as it's pretty low priority.

Alan C.

Three out of whatever number of GT4s shipped to CA is a huge PPM number.

Spyerx

Hopefully before end of year I'll have mine on a dyno stock and will try 91 and 100 stock to see difference...

stout

Two samples in two parts of the state will be better than one.

If you beat me to it, just remember the ECU will need time to decide it's on the improved fuel and alter parameters to take advantage of it. It may be better to go in on the end of a tank of "93", then switch to 91 pump gas and run the car around for a while before strapping it back onto the dyno. Of course, ambient temps, pressure, heat soak, and all the other joys of chassis dyno tests will be present. Even so, hopefully we'll get some useful hard data or at least some clues as to how the stock ECU is working with 91 vs. 93+.

Stgrt

Deleted.

cox1974

Mine with 100 octane fuel and on "hubdyno" showed 390 flywheel hp... totally stock...

ExMB

For ref
EU 95 octane = US 91 octane and EU 98 octane = US 93 octane i.e your EU 100 is close to 94.5 over here

Da Hapa

Late to the game and haven't tried mixing fuel in my GT4 yet but FWIW, my old 997s responded very well to mixing 100 octane with our crap CARB mandated 91. This 76 is in the same shopping center as my old vet and where I regularly mixed fuel in that car (esp. during hot summer months) to good affect.