Riptide

Ah OK. Well he swears he could tell a difference in his car between the 91 and 93 without loading a tune. This is a 2002 WRX.

dbspcl

There is no way the computer in a 2002 WRX does what the new adaptive knock-sensing/timing-adjusting algorithms do in the 2008 Bullitt. The technology just wasn't advanced enough.

Perhaps your friend's WRX was experiencing detonation with 91-octane? And putting in 93-octane got rid of that detonation, and he perceived it as an increase in performance?

Riptide

Maybe. But that car shouldn't require 93 octane to run knock-free. The manual says 91.

Legion5

1. your friend could have had an adaptive tuning car, but this is highly unlikley as the bullit got a lot more press for it's adaptive tuning than it should have if it wasn't an industry first. They definitly acted like it was.

2. your friend judged the increase because the engine had carbon build up and which was causing knocking. His car needed 93 because he didn't take care of the engine, causing his cylinder to agitate the gasoline and spontaniously detonate it reducing power. Not that I'm saying that's what happened, but his car should have also sounded slightly different if that was the case.



On our cars the compression is already high enough to take advantage of premium gas. What Ford did was they made the ignition timing very retarded to "cool off" the cylinders essentially artifically lowering the compression by not taking advantage of it with advanced enough timing. The retarded timing caused the engine to run cooler and agitate the gas into exploding less allowing 87 fuel, but the engine wasnt running in its "ideal" ratio all around as a normal engine designed for 87 gas would have.

While it is impossible to "retune" an engine with just software to effectivly run higher octane gas and not waste money and such, Ford "retuned" the engine to run lower octane gas which is possible.

Our engines are effective up to 100 octane Ive heard, and after that you have to start changing out heads to get any effect from high octane obviously.

This may sound complicated but trust me its accurate. They make 100 octane tunes and those are very powerful, but the OP does not have that tune so running the gas would just be pointless.

Mishri

As was said by someone else later in the thread.. we've never heard of anything over 100 octane that is unleaded.. and he mentioned 100, 105, 110..

Stoenr

Now that would be cool, lol.

kcmarti

I did mention "appropriate tune" in my original post, but did not realize that the fuels above 100 octane were leaded, I could have sworn that the at least the 100 and 105 were marked unleaded. I will have to check that out again.

With an octane appropriate tune, can our (NA) cars benefit, performance-wise, using 100 or 105 octane unleaded fuel? Or is 93 octane the the "practical limit" on any performance increases?

AmericanSpeed

I don't think you will see gains worth the price difference with the 100 or aboveand the NA engine (I think I've seen 104 unleaded). It's one thing to tune for 93 when its only 20 cents more than 87. But 100 octane is usually about 3 more dolllars per gallon, prob not really worth the performance gain. Then again, I've never tried it, so I'm just speculating.

Riptide

Not having a great understanding of engines can someone explain to me what effect advancing and retarding timing has? I realize that higher octane fuel allows you to advance the timings. I don't understand the mechanism involved with the power gains there. Thanks

AmericanSpeed

Advancing the timing allows for more gas to be used efficiently. Wikipedia gives a pretty good explanation on how ignition timing works.