Quick Octane/fuel grade question...

[kaffeene]

Hey, I just wanted to know what grade fuel/octane everyone is using for there 4.0. Particularly YJ's.

I am using mid-grade, 89 octane. Correct me if I'm wrong but I beleive the compression ratio of a 95 4.0 is 8.8:1 so 87 Octane will suffice.

ANY INPUT????

[Simba]

use the lowest octane that you can without problems. My 2.5l now requires midgrade to avoid detonation. It has 125k on it too. Mileage is a big part of that question. I also run premium 2-3 times a year with a little octane booster if I know that the entire tank is going to be highway.

[Joe Dillard]

For the past 9+ years my '91 4.0 YJ has been running fine with 87 octane with zero problems with this gas.

Clean spark plugs, good wires, good spark, good air filtration system, and good exhaust system seems to make it run just fine. :)

[TBone]

I agree, just run the cheap stuff, unless you have detonation/pinging

Im at 140,000 mi on my YJ and 150,000 on my CJ both running great. I dont konw if it helps but I try and say with the same vendor of gas, usually Hess. I figure that I will have more consistant performance from the same fuel all the time.

Tom

[Schmozilla]

I've always run 93 in my MPI 258 and i still have a litttle sign of pre detination on the plugs.

[kaffeene]

any other input??