Raising the 4.0's Compression??

[eric91xj]

how many people out there have raised there compression on their pretty much stock/bolt on modded 4.0's? What are some realistic power gains to be expected by raising it to say maybe 9? 9.1? 9.2? and along with that any issues that will come from doing this?

thanx,
eric

[Eagle]

What year XJ? If it's a Renix ('87 thru '90) you'll be creating knock, which the knock sensor will attempt to fight by retarding timing. Unless you plan to run 93 octane, you may lose power rather than gain it.

The '91 and newer don't have a knock sensor, so raising compression will definitely require higher octane fuel. I won't speculate as to how much of a power gain you might see, but I doubt it will be worth the expense.

[eric91xj]

gotcha, just pondering the idea, thanx