So, I've been reading on a few forums that the Jeep 4.0L, 232, 258 etc. have a resonance at about 6000 RPM and it will do all sorts of horrible stuff like cause your distributor to pop out, snap timing chains, an odd broken crank etc. Supposedly "All L6es have it" as well and you can "drive through it."

Am I right to be skeptical on this, or should I actually pay heed to it?

 

4.0l efi combos
All i can add, guys run these in rock climbers and such. Ive been in and seen peeps with them on the floor bouncing off the rev limit with no fail. Cracking the heads is another thing.
I dont know what the rev limiters are factory.

 

Not near 6K. The cam is something like 188/[email protected]. Still working out how the valve train will look to make that happen; I should probably order the cam I'm thinking at least and go from there. Custom is gonna take a while to make happen.

Head cracking is because of a design flaw for a few years around the 00s. The later "TUPY" supposedly fixed that.

 

All i can add is if it truly has this issue , a better damper would be the first place to start. Otherwise I would guess its in the crank design not having enought material to keep it from flexing. I would expect main bearings to show this dramatically as some would get beat hard if it was drastic enough to break a timing chain.

 

maybe those jeep engines weren’t made to rev high and the engineers who designed it didn’t think it was necessary to fix an issue not many people would have a problem with. Like t bird said a good aftermarket balancer is a good place to start.

 

Probably true but then again that's also probably true of most pushrod engines made up into the early-mid 00s. Like anything else you have to understand the limits and whys in order to work around it.

The Internet also says a lot of things though.

 

I agree