Fuel/octane questions

[Turbo Monk3y]

Well i have a small problem due to still having a stock fuel system. I have my MBC set at 15psi. In 2nd gear it creeps to 16 psi at redline, And at 6500 rpm in 3rd its at 17psi then BAM!!! i hit fuel cut. Same thing happens in 4th gear... Now my problem is that Im going to the track this sunday and i cant get my walboro 190 till next week or so. There fore I will go to the track but i will put in a mix of 2 gallons of Xylene and a 1/4 tank of 93 pump gas, and 10oz of marvel mystery oil.. My question i have Will this keep me safe at 16-17 PSI on a stock fuel system?? The octane rating should be somewhere 98.5-100. The highest its ever creeped to at redline is half way between 16 almost 17 psi. i really dont wanna hit fuel cut again and i will also be shifting at 6700-6800 rpm anyways. I also figured around 17psi on a stock fuel system will be getting into a high knock count and timing being pulled so this higher octane will help to keep the knock low if any at all.

 

[Groomz]

Octane won't change when you hit fuel cut. Fuel cut is based on airflow. You have to eliminate fuel cut or decrease the amount of air the ECU "see's" with a S-AFC/II. The higher octane will net you more ignition timing, but won't help with fuel cut.

 

[Mike 99GSX]

Exactly what he said except it won't net you extra ignition timing either without dialing back the airflow signal more. You need an AFC

 

[Groomz]

Originally posted by Mike 99GSX
Exactly what he said except it won't net you extra ignition timing either without dialing back the airflow signal more. You need an AFC

Even on a completely stock vehicle, there are power gains from raising the octane value. I ran 100 octane toluene mix in my stock 95 TSi and noticed a significant power increase. Enough also for other passengers to notice. I don't have a pocketlogger but I would bet that I was picking up at least 5 degrees extra timing with the 100 octane at the same boost. Its a trade-off. Either you can have more timing at the same boost or the same timing with more boost, hence the reason most people run higher boost on race gas. Also toluene has is more dense than gasoline, which yields to more power being produced per unit of fuel.

 

[Mike 99GSX]

You get more timing with race gas by lowering the airflow signal and getting into a more aggressive map. If you just dump in race gas and don't alter the airflow signal, you will not receive any more timing advance.

 

[nine5raptor]

If you were knocking previously, then you will gain timing (lose the retard) without altering the signal.

 

[Mike 99GSX]

Good point. I probably overgeneralized my statement. I was assuming the car was already set up properly for low knock on pump gas prior. It potentially wasn't after rereading his original post

 

[nine5raptor]

And, unfortunately for most of us 2ger's we can't tell if we really are knocking or not