Head work?

[Cobrajay]

Well, I blew the 4.0 up...over heated it so damn bad that I bent the valves in the head and melted a couple pistons. Anyways, i'm picking up a junkyard motor soon and I really want a little extra HP. I was thinking of porting and polishing the head but I called a shop and the guy said "yea, u can do that but a valve job would give me 30 extra hp" Will cost $400! Plus, im getting a 99 intake so this all sounds nice. Has anyone done this b4? Thoughts please op:

 

[yossarian19]

30 HP is a bogus claim.
If you want extra power, build a stroker with a 4.0 and 4.2 crank / rods.
Other than that, follow some tips from : http://www.angelfire.com/my/fan/

 

[AIbandit]

Get the DIY kit
http://www.jeep4.0performance.4mg.com/head.html

 

[gradon]

You can get 20-30hp out of a good port and polish and a cam that'll take advantage of the better breathing head. I'm working on a head for my brother's 4.9l turbo comanche build using the Standard Abrasives Kit and the carbide deburr kit purchased from summit:
http://www.summitracing.com/parts/SAI-260001/
http://www.summitracing.com/parts/SUM-900640/

 

[Talyn]

home port and polish, 30* valve back cut and a 3 angle valve job. Maybe run you $200 in machining work on the head.

 

[KillerCOM]

DO NOT, polish the the intake ports. Do your port work by starting with a fresh gasket, and finish with 40 to 80 grit cartrige rolls. Have your combustion chambers polished to combat detenation. You can polish your exhaust ports though. I'm finishing my head right now at UNOH. My intake flows 217 cfm and the exhaust flows 163 cfm, all with stock valves. I'm going to stick with factory valves but they will be back cut, and a set of 1.7 roller rockers instead of a cam swap. This head is also getting decked to bring the static CR up a bit.

 

[Dr. Dyno]

My intake flows 217 cfm and the exhaust flows 163 cfm, all with stock valves.

Do you have the rest of the flow numbers? I didn't get my own ported stock head flowed but the numbers are probably very close.

 

[gradon]

Hey Killer--dunno if you got your head on yet and/or if you have the stock valve springs, but the stock springs can't handle the additional lift the 1.7s provide(they bind at .43"lift and the 1.7s will make 87-95 cams .451" lift). Buy the p5249464 springs if you have any lift over .43".

 

[KillerCOM]

I'm not going to use the stock springs, I'm going to use comp's springs for the 4.0 or do the machine work for a double spring. Yea i'll post my flow numbers for both stock and ported. I've been talking to a leading AMC engine builder about everything i'm doing so I don't mess up, thats the good part of working at the Jegs Engine Masters Challenge. You get to Bs with some really sharp guys...

 

[Talyn]

What comp cam 4.0L springs? If they are the ones in the cam kit they aren't for the 4.0L. Also, there is no need for a double spring for any street able cam on the 4.0

 

[KillerCOM]

Computer is messed up will try to post numbers at school one day this week. Sorry.