4.0l Revs

[MrBClark]

This probably seems like a stupid question but how high of an rpm can the 4.0 handle? I generally shift around 2800-3k rpms but can the 4.0 handle 4.5k every once in a while? Sometimes its just a bit more, well, fun to shift that high. Dont get me wrong, I don't try to kill this engine, just every once in a while when its fully warmed up I will take it that high. Can it handle this?

 

[AjRagno]

Not only can you rev to 4,500 RPMs, you should do so frequently to remove carbon deposits. Part of TSB 09-003-03 involves selecting a gear that allows for driving at 4,500 RPMs for 15 seconds.

 

[Steel City 06]

When accelerating hard I frequently shift right at redline (~5,200 RPM). I occasionally hold 4500-5000 RPM at full throttle for a few minutes while ascending hills on the freeway.

It won't hurt your engine at all. Definitely safer than lugging it.

 

[Goatman]

The red line is called that for a reason.

 

[MrBClark]

The red line is called that for a reason.

So that means... can it handle 4.5k rpm?

 

[Jerry Bransford]

Revving it as high as recommended above is a good idea to do on a semi-regular basis. If you drive an engine too conservatively it will eventually load up with carbon and start running crappy, including knocking and pinging.

 

[qslim]

I still haven't gotten around to re-gearing & am running 33s with 3.73 gears, so in the around-town driving my TJ usually sees I rarely shift out to 3rd to keep the engine in the 3k rpm range. Like everyone already said, lugging the engine isn't a good thing, and our inline six has no issue operating in the 4.5k range.

 

[Goatman]

I try and shift hard through the gears at least once a month. Certainly 4500 rpm all day every day is less than ideal. But a bit of spirited shifting helps clear out carbon buildup, keeps the rings from forming a ridge near the top of the bore, and pushes enough oil pressure to help flush lifters.( that last one is opinion ).