What would a 2000-2001 RS with headers, a cat converter, and a cat back, need to use for gas? (87 octane )

 

I'm not an expert, but I think one of the main reasons to use higher octane is to avoid detanation, so unless your running boost and there for increasing the temp in your cylnders you should be fine running 87. And since all your mods are post combustion I'm like 99.9% sure that they don't matter when it comes to picking an octane.

 

That would make sense... I was just a little worried because the compression is 10:1, but thank you for putting that to rest.

 

ur fine at any till ya start boosting.

 

Your ECU in your RS requires you to run at least 87 octane gasoline.
You will be fine running 87 octane unless you turbocharge your RS than
you will have to run at 91 octane or higher.
The only thing I highly subjest is running good name brand gasoline in
your RS so, it will run correctly because cheap off-brand gasoline sucks.

 

Wow, my first post!

If it's got 10:1 it could probably pick up some HP by using 91, but ONLY if the ECU were re-tuned to take advantage of it. Usually the factory retards the timing curve with higher compression engines to allow them to run on low octane stuff...

 

ej25 is built for 87 octane. Forced induction (and the resulting fuel/air mix) requires higher octane because you end up with a higher pressure in the cylinder. It's the exact same reason that higher compression ratios require it, because the pressure is higher since the cylinder compresses the mixture more (compression - same number of molecules, less volume or turbo - more molecules, same volume). You will not gain power by using 91 octane in a stock ej25. RewSupul is right, unless you get early detonation, don't use 91 octane, it's a waste of money with NO advantage.

 

I think the manual recomends 91 for best performance. Actually, I'm sure it does. You can get away with 87 though if you wanna be cheap about it. I don't run anything less than 91 in all my cars. Then again, I'm at 5,000 ft. I use 104 in my subaru.

 

i'm not sure if i'm experiencing the 'placebo-effect' on octane gas but i believe so that i'm getting more power with higher octane gas.

i got a 2.5i 4EAT and usually, when floor the pedal sometimes, i get a quicker response and more pull with 91 octane gas (from chevron btw) my current fill up is full tank of 87 octane. I tried flooring it and it was kind less responsive.

I checked with the manual and it says that you can use 87 octane or higher,.. soo.. having that said n' done,.. who cares... :P

 

91 for me, but the car is new to me and I am just trying to clear up the engine some.

 

Ya, the 06 manual says 87 for 2.5I, 91 for WRX and 93 for STi