I wonder about the performance difference between unleaded and super.someone would try it?

 

Your stock engine is designed for regular. Unless you have made some changes to your engine that call for premium, you are wasting money.

 

yes you are right .but I believe the dealer can flash ecu
and motor can run with premium. so somebody do it or have information about it?

 

There is no reason to run extra octane. Bumping the timing a few degress with a tune is a negligible increase in power. Unless your running a supercharger, have a high compression ratio, or have extensive mods, there is no need for anything more than 89 octane. Your pumping money away into the atmosphere by running premium gas in a 3.8L or even a hemi swapped JK unless it's a 6.1. It's just not needed and not wise.

 

Supposedly higher octane fuel burns more completely and is supposed to prevent deposits from forming in the combustion chamber. I have heard from some drag mechanics that you should run high octane once or twice every month or so to clean old deposits out.

The logic kind of makes sense but I haven't seen any actual testing to prove it true. I would stick with the low-tech 87 unless you like to spend your money on gas instead of mods.

 

I ran 89 octane on a trip back from Cali once, to see if I got up the big climbs to Vegas with less gearing down...Engine light came on about 100 miles into the trip. I filled up with 87 when I got back and the light went off after a few hours of driving in town.

 

I put 186,000 miles on my XJ running regular and had no deposits to speak of. The piston tops and head chambers were quite clean.


Edit to add:

Responding to jiggawha, below: never ran any kind of cleaner through the fuel system.
Not saying it's not a good idea, I just never thought of it.

 

+1 on this. Buy good gas and run a fuel system/injector cleaner through with every oil change. I've always had good results going on that path.

 

Spend your extra dough on better gas. Top tier gas includes, Mobil, Chevron, and Shell.

Shell's new gas is nitrogen enriched. You will see alot of ads about this soon. I am a Shell dealer and from my experience feel it is a better fuel.

F all the people that say gas is gas. It's like saying all vodka or wine is the same.
And run 87 octane. The engine is designed for it. Not the hotter running 93 UNLESS as posted above you have specific mods done.

FWIW, I ran the Hypertech programming, and 93 for about 2 weeks. Blah... don't bother. I like the Hypertech, but the 93 is a waste of time.

 

This is not true. Lower octane fuel is not lower quality fuel. This isn't the 1960s. Higher octane fuel burns slower to prevent harmful spark knock on engines prone to have it, ie supercharged, high compression over about 10:1, etc. It's been dyno proven that running a higher octane fuel than required actually REDUCES power on an engine not needing it or designed for it.