port and polish the head.

T

TheLaredo

NAXJA Forum User
Location
SoCal
So I was talking to another Naxja guy here and was playing with the idea of porting and polishing the head of my 1991 Cherokee. I got a good valve tick going on so since I need to probably do some work on the head already, might as well go all out. So the question I guess is, how much meat is there and how much more power could I see from doing this? Is it even worth the work?

Edit: Also, is there any particular reason as to why I cannot view attached images here?
 
Exhaust ports don't need "porting", I say that because the ports are too big already..We can't flow enough exhaust and actually get revision! Theres gains on the intake side & chambers though! I'm no expert, I just read that FAQ on jeepstrokers..it explains alot! Theres a bunch of info on jeepstrokers, with alot of flow work testing as well to back up the claims!!
You can clean up the head & gasket match it all and that'd be a nice upgrade! Put a mirror finish to the exhaust ports & the chambers! I'm hangeling for a 0630 ported head right now...looks great and for 300 bones I think its worth it!
 
Just a word of caution when it comes to the port in a cylinder head.
It is very easy to hurt air flow in a port if it isn't done properly.

What is the most important and most overlooked is a precision valve job, and the bowl area just blow the seat. The further you get away from the valve seat, the less critical it is regarding airflow.

I'm not saying you can't do it yourself. If your careful and do some homework on the subject you can get some improvement but has been my experience that in many cases the results are a disappointment.
 
Just clean up the casting and then polish. Don't really attempt to modify anything. Check head to intake and exhaust manifold alignment, modify so the air doesn't hit a wall, if any.
 
You probably don't want to actually "port" the intake and exhaust runners. As mentioned above, you can do some real damage (power-wise) if you do it wrong. There's a lot of science, and also quite a bit of art in porting. Without tested runner profiles to work to, you have no idea what you are getting.

What you can do is "port-matching" and polishing: making the transition from the manifold to the runner as smooth as possible. The object is to match the openings in the intake, head, and exhaust manifold with as little misalignment as possible, then smooth the runner and remove flashing from the bowl area. There are several good videos on youtube, and here's a pretty good article from the powerblock TV website. 'Format is kind of irritating, but the info is worth getting. Short vid at the end too:
http://www.powerblocktv.com/magazine/?pub=36335&page=45

By the way, the valve tick is probably a lifter problem, and not a valve problem.
 
I've always wondered how much it would cost to have a head made for a 4.0l where the design put the exhaust on the spark plug side and left the intake on the driver side... It be tons-o-money and might not be worth the iron the head was cast in but, i so hate the way the head is setup now... Sorry to high jack... Yeah, I have read alot on it too, just recently changed out the head on my '90 Renix rig and from what I've read you really don't get much gains with a port and polish job. I had it in mind since I would have it apart, but you gotta spend lots of money on the head to get any appreciable gain from just the head alone.
 
casual said:
Exhaust ports don't need "porting", I say that because the ports are too big already..We can't flow enough exhaust and actually get revision! You can clean up the head & gasket match it all and that'd be a nice upgrade! Put a mirror finish to the exhaust ports & the chambers!
Click to expand...

Agree with the last statement but having ported three 4.0 heads in the past, I have to disagree with the rest. The exhaust ports are where most of the power is hidden. Begin with a good blending of the valve bowls/throats, smoothen the short side radii, and teardrop the valve guide bosses. This will also work well on the intake side but the results are even better on the exhausts.
The exhaust valves suffer from slight shrouding in the chamber so just cut back the chamber wall slightly, keeping the edge flush with the head gasket fire ring.
The intake ports don't need to be enlarged but you should try to match them to the intake manifold runners, so you might need to lightly modify the gasket as well. The exhaust ports are definitely too small so they can be opened up, but stop short of matching them to the gasket 'cause you'll then have reversion problems.
You might find these pages helpful:

http://www.jeep4.0performance.4mg.com/head.html
http://www.angelfire.com/my/fan/prep.html
 
Aww ok I had it backwards lol..Dr Dyno = dino right?
Can you explain what you did or added to your oil pan as a windage tray or possibly make a template for me? I want to do this while I'm rebuilding my motor...Might as well since I'm there.
 
He added a baffle to the oil pan. Basically welded a piece of steel plate on to the back of the sump to keep the oil from riding up the back of the pan. Just make sure you have enough clearance to put the oil pump pick up in.

Here is my windage screen:
P1250434.JPG
 
casual said:
Aww ok I had it backwards lol..Dr Dyno = dino right?
Can you explain what you did or added to your oil pan as a windage tray or possibly make a template for me? I want to do this while I'm rebuilding my motor...Might as well since I'm there.
Click to expand...

Yup, that's me. :D
As Talyn said, I just added an extra baffle at the rear of the sump. Since I also swapped in a high volume oil pump at the same time, I had to "massage" the oil pan with a ballpeen hammer to gain some clearance from the larger oil pump body.

http://www.angelfire.com/my/fan/HVOP.html
 
Yes, off the main girdle. I made a skeleton (rib cage sort of) welded to the girdle to mount the screen to and give it structure. The screen is held to the skeleton by solid rivets and some welding.
 
A lot of hi-perf. engine go one step further and use a crank scraper. This is a piece of sheet metal formed to match the crank/rod setup as close as possible without touching to catch any oil as the crank throw rotates up away from the oil pan. I've seen a couple cut so close they had small divots to clear the rod bolts.
 
You must log in or register to reply here.

Similar threads

rang-a-stang
4.0 Head is cracked. Any other upgrades I should do when I am in there?
Replies
4
Views
396
Ol Blue
Ol Blue
A
1989 Rennix Head Gasket kit
Replies
6
Views
289
lawsoncl
L
G
1997 XJ won’t rev high and loss of power
Replies
8
Views
313
Tim_MN
Tim_MN
Alboy97XJ
Rubicon Trail Foundation Work Day June 21st 2025
Replies
8
Views
488
Goose_XJ88
Goose_XJ88
N
CHMSL and socket?
Replies
4
Views
198
Saudade
Saudade
Back
Top