flamin-roids

Well I was always under the impression if you are running a fairly stock N/A that running 85-87 octane fuel was ideal right? Well I've been running 85 for a while and the car did run fine. Just felt kinda slow at top end. I started putting 91 octane in and for some reason. A huge difference! Better gas mileage and the exhaust seems to be less thick. And quite a bit more power. So 91 octane shouldn't guarantee more power I'm sure. And its supposed to "less" combustable. So what would explain my cars significant boost in performance by using 91 octane?

RotaryEvolution

iTrader: (30)

check your timing, if it is off then octane can have a drastic affect on your engine performance.


edit: i would also suggest checking your plugs and wires, if the wires are old and worn or the electrodes on the plugs are worn to nubs then this could also affect how the fuel burns and octane would affect it's combustion. be sure your trailing coils are firing also.

GT-R

Octane ratings are basically to combat "detonation" in a higher performance car, which is why 99% of Turbo cars require atleast 93 octane.

However, I was told a while back by my Vo-Tech teacher, while studying the dark arts of automotive technology (Mwwaaaaahhahaahhaha) That a higher octane is for a hotter "boom" essentially.

The higher the octane, the longer the fire burns. Now, I'm a piston-head for a long time, new to rotaries.... But I'll explain it in Piston-block form.

The longer the fire burns, the longer the force of the explosion drives the piston downward, the longer the piston is forced downward, the more power it gets. While its not exponential or entirely noticable on alot of cars. It is rather noticable between differences of octane when in a carbuerated car, which spits fuel into the car indiscriminate of what its "set" at.

If your car is carb'd, I would say that this is what you're experiencing -- which is normal. You're -supposed- to, I think, get more gas mileage out of better octane. But thats the way I've always interpretted it...

Correct me if I'm wrong, I gladly stand and be corrected, than to let someone wander about without an explaination


EDIT: Also, to answer your question, maybe you're losing compression. Higher octane, like I said, fights detonation -- low compression = risk of detonation ..... I think... Don't quote me. But my WRX runs 8.5:1 and thats hella low compression for such high out-put, and it HAS to be run on 91 (I run 93) or else it will send the knock-sensor into a ****-fit.

RotaryEvolution

iTrader: (30)

you are for the most part correct but the timing is a key factor to the ignition of the gas, if it is ignited too late then most of the force will be lost as the rotor has already past the peak point that it needed the combustion. same principle with a piston engine.

lower compression has a less chance of detonation, hotter rotor and piston face temps and a low density air charge with a low octane will ignite without an ignition source(spark plug spark), mainly why you should try to keep as much carbon off the face of your pistons and rotor faces as possible.