head questions

[shawnxj]

ok so i've read that porting a head moves the rpm up out of the typical 4.0 operating range. so my question is what does putting in chevy valves do to the usable rpm range? and what would happen if you put in a 2.02 intake but leave the stock exhaust valve do? or say porting out the intake runners but not the exhaust? how much of a difference do roller rockers make?

i have a 0630 head and i can't seem to decide what route would be the best for me. i'm getting my block back next week maybe and so far i have a 99 block punched .020, stock 4.0 rods, kb944's, a 258 crank, and a 99+ intake/throttle body/injectors. i still haven't decided what cam to go with mainly because i can't decide what to do with the head. i want to keep the torque as low as i can because this is gonna be a mainly offroad xj but it will see the highway alot.

also since i have a longnose 4 wt crank what harmonic dampeners would be the best to go with?

[SilverXJ]

I haven't heard of larger valves doing anything good for the 4.0l due to valve shrouding issues, and the valve isn't the bottle neck.

As for the harmonic balancer there is nothing preferred. Just get it balanced.

[Cheromaniac]

i have a 0630 head and i can't seem to decide what route would be the best for me. i'm getting my block back next week maybe and so far i have a 99 block punched .020, stock 4.0 rods, kb944's, a 258 crank, and a 99+ intake/throttle body/injectors. i still haven't decided what cam to go with mainly because i can't decide what to do with the head. i want to keep the torque as low as i can because this is gonna be a mainly offroad xj but it will see the highway alot.

also since i have a longnose 4 wt crank what harmonic dampeners would be the best to go with?

Keep the stock size valves, do a pocket port job on the head, and port match the intake ports to the manifold runners. For the exhaust ports, just do a light clean up of the rough casting and polish. A good cam choice is the CompCams 68-231-4, though the 68-232-4 will give you a little more torque at lower rpm at the expense of upper rpm torque. Go for the Mopar Performance 5249464 valve springs with matching retainers and keepers. The CompCams items are not compatible with the 4.0L valves.
You'll need a 4.0L harmonic damper plus a 1cm thick spacer placed in front of it to keep it properly aligned with the other pulleys.

[shawnxj]

thanks dino and silver

[jbxx]

Keep the stock size valves, do a pocket port job on the head, and port match the intake ports to the manifold runners. For the exhaust ports, just do a light clean up of the rough casting and polish. A good cam choice is the CompCams 68-231-4, though the 68-232-4 will give you a little more torque at lower rpm at the expense of upper rpm torque. Go for the Mopar Performance 5249464 valve springs with matching retainers and keepers. The CompCams items are not compatible with the 4.0L valves.

Could you elaborate on this statement? Are you saying that if I use the Comp 68-232-4 cam with Comp lifters,
Mopar springs and hardware, that it will not be compatible with the 4.0L valves? I'm confused!
Thanks J.B.

[SilverXJ]

He is referring to the comp cam full kit. Its the comp cam valve springs, retainers and locks that don't work with the 4.0L valves.

[jbxx]

Got it! Thanks.
J.B.