Port & polish question

I'm thinking about porting & polishing my head as well as possibly getting it milled slightly-

I have a '92 XJ with 115K that runs very strong. If I do a moderate port and polish I'm thinking I should be able to gain some power without losing low end. Possible? Should I just do a full-scale port? What are the chances of me losing low end? I don't spend much time over 3000RPM but I'd like it stronger on long hills and mountain passes. I have a large exhaust and 60mm TB already, header coming soon.

Milled- I'm thinking of doing this just to squeeze a little more out of it, good idea? How much should I mill and what would I expect to get out of it? I don't mind using high octane gas, I live at 4500 ft and spend a lot of time higher than that so the increased performance would be nice.

Thanks-
SCW

Milling is something you'll want to think about. Since the preload on the lifters is not adjustable, milling overmuch will require a new set of pushrods. I'm sure Dr. Dyno could tell you more - but if you took .030" or more off of the head, I'd think about pushrods made to length as well.

Port work (beyond simple polishing and smoothing) should not be entered into without a flowbench - it's too easy to screw up and take too much off. Just clean the port up - especially the intakes - and remove only the material needed to clean up the "sand-cast" finish. More than that should be left to people with a shop available - since true port work also requires more than a little knowledge, and more than a few tests per port. It's possible to work one out and duplicate it everywhere else, but it's safer to test each port at intervals during cleanup and re-shaping. Besides, those ports tend to be carefully designed, and you don't want to screw that up, do you?

You might want to think more about re-gearing - you don't say how you're set up.

5-90

Id look into building a stroker before i blew my money on milling and porting/polishing. Stroker motors are VERY reasonable and fairly easy to build and will give you much more of a usable performance gain that what you would get with a port job.

A simple port cleaning and gasket match is a easy home job and generally worth every penny you spend on sanding spindles. That should not hurt your low end. Though opening up flow through the entire system will. You need to keep your air velocity up at low RPMs and you are not going to do that by making the holes on the intake side bigger.

You state you are at 4,500 ft and often go higher.
Here is the problem as I see it: You are trying to polish a turd by bolting things on it. None of which is going to fix the cause of the problem, the lack of air density at altitude. To fix that, you are going to have to cram more air in to mix with more fuel. To do that, you need a supercharger, a turbocharger, or more cubes. Thus Jeffro600's stroker suggestion.

5-90s idea of changing gears will allow your XJ to pull more with less available power.

SCW said:

I'm thinking about porting & polishing my head as well as possibly getting it milled slightly-

I have a '92 XJ with 115K that runs very strong. If I do a moderate port and polish I'm thinking I should be able to gain some power without losing low end. Possible? Should I just do a full-scale port? What are the chances of me losing low end? I don't spend much time over 3000RPM but I'd like it stronger on long hills and mountain passes. I have a large exhaust and 60mm TB already, header coming soon.

Milled- I'm thinking of doing this just to squeeze a little more out of it, good idea? How much should I mill and what would I expect to get out of it? I don't mind using high octane gas, I live at 4500 ft and spend a lot of time higher than that so the increased performance would be nice.

Thanks-
SCW

Click to expand...

Read this:

http://www.jeep4.0performance.4mg.com/head.html

Zuki-Ron said:

You state you are at 4,500 ft and often go higher.
Here is the problem as I see it: You are trying to polish a turd by bolting things on it. None of which is going to fix the cause of the problem, the lack of air density at altitude. To fix that, you are going to have to cram more air in to mix with more fuel. To do that, you need a supercharger, a turbocharger, or more cubes. Thus Jeffro600's stroker suggestion.

5-90s idea of changing gears will allow your XJ to pull more with less available power.

Click to expand...

Stroker is the long-term plan, everything I do now is intended to be a precursor to my stroker, but the car is a DD and can't be taken down for a rebuild yet. By the time I do the stroker I intend for every other component to be ready and simply be moved from one block to the next.

I expect the head to cost a grand total of $250-$300 including milled, ported etc. I'll reuse the head on the stroker down the road as well, so it's not money wasted.

I'm running 235/75/R15's now with no lift, but eventually I'll give it a 2" lift, no more. The 3.55 gears are a little high, but I don't see the economy of regearing to 3.73 and 4.10 seems too deep for my purposes. The economy of engine mods works out, as long as it keeps with the long-term stroker plan.

So...port & polish won't hurt the low end and should give me a little boost in performance? Should I get the head milled? How much should a stroker head be milled- that's the max I'd want to mill it. I may be looking at custom dished pistons with the stroker but I'd hate to lock myself into that right now.