Smogrunner

iTrader: (5)

I'm having an argument with my friend: when my evo is tuned for 100 octane (A/F, boost, timing), can I run C16 117 octane with at least as good results as 103 or 104 unleaded race fuel? He says the C16 will actually hurt performance, while I believe the C16 will perform at least as good, maybe better than the Sunoco 104unleaded. In this case, I am concerned about drag racing applications.

MalibuJack

iTrader: (5)

Nope.. It won't hurt performance.. Stay away from leaded race fuels though, we all know they damage the catalytic converter and will eventually kill the O2 sensors in the car.

Sane OO7

malibu nice site

ducaticorse

what he said

ShapeGSX

Don't worry about the O2 sensor. I run about 2 to 3 gallons of leaded gas through my car during the race season, and I've enver had an O2 sensor go bad on me. They slow down right after running it, but they pick back up a week later.

And yes, running the higher octane can hurt your car's performance if you don't tune for it. That is why I tune my car differently every time I go to the track. One tune does not fit all circumstances. Higher octane fuels require more timing advance in order to get the highest pressure at about 15 degrees after top dead center.

As well, different fuels have different specific gravities, which can alter the fuel delivery.

Read "Forced Induction Performance Tuning" by A Graham Bell if you want to learn more. It is a great book.

jbrennen

iTrader: (1)

From my understanding, ShapeGSX is right... Blindly running higher octane may hurt horsepower. In general, higher octane fuel has a more controlled burn -- thus a slower burn. If you burn 117 octane, but use 100 octane ignition timing, your peak cylinder pressure will come later in the power stroke. Unless you (or the engine management) either lean out the mix or increase boost to compensate for the delayed burn, I would not be surprised at all to see HP numbers actually drop.

metaphysical

iTrader: (3)

REAL WORLD:
My evo - Buschur Exhaust/Airfilter/Dynoflash
No Boost Controller - Tuned 93 Octance - 264WHP

Over half a tank of Sunoco 94
103-4 MPH Trap

Dumped four gallons Blue 112
106.5 & 106.75

Unfortunately, my tires are shot (one on secondary rubber),
So, I just squirmed and spun off the line with the added power.

ShapeGSX

metaphysical, if that is the case, then you were either knocking on 94 octane, which would have retarded timing and taken away some power, or the 94 octane fuel was oxygenated whereas the race gas was not.

My guess is that you were knocking, though.

Oxygenation robs your car of power. Smog, however, was talking about going from one race gas to another race gas. He would not have the oxygenation issue. But most areas do oxygenate pump fuels. Race fuels are not regulated in this manner.

There are a lot of properties of fuel that are not expressed with octane. There is the latent heat of vaporization, the specific gravity, the spread between motor and research octane, lead content, etc... And different fuels are more suited to forced induction than others, even if they both have the same octane.