Port and polish

Does anyone have a link to a 4.0 liter specific port and polish write up, i'm planning on doing it at the same time as my stroker and would like to find someone w/ some pics and info to make it easier.

i did search but couldn't find a 4.0 specific write up

You might find a tidbit or two here...
http://www.colorado4x4.org/vbb/showthread.php?t=80410

Also, Google <Standard Abrasives>. They do a DIY port/polish kit, and have a decent writeup on their website somewhere.

While it's entirely possible to do some cleanup work, doing significant flow improvements is beyond the reach of the average home mechanic and DIY-er. It's not techically difficult, but it requires a flowbench and regular testing in order to make sure you're actually improving flow, and to make sure you don't do too much work and end up reducing the benefit of all the work you're trying to do...

5-90

5-90 said:

Also, Google <Standard Abrasives>. but it requires a flowbench and regular testing in order to make sure you're actually improving flow, and to make sure you don't do too much work and end up reducing the benefit of all the work you're trying to do...
5-90

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What he said, that colorado 4x4 link shows a guy who obviously went overboard and has created a nice high pressure pocket where his intake and head runners meet. If you "hog it out" like he did, not only do you stand a good chance of finding a coolant passage; the very expensive way; but you'll also create a pocket where the air can "expand" and increase the back pressure FIGHTING intake velocity and more than likely lowering HP and Torque by small amounts.

Look at the design of a Jet Engine, they are always larger inside the scoop to allow the air to increase in pressure right before -- or even inside -- the combustion chamber thus giving a "free" boost pressure increase. Increasing air pressure for free is good... as long as it's not being increased in an area that will create lower velocity, extra back pressure, drag and turbulance, before the runners decrease in size again.

This stuff is seriously counter-intuitive, but suffice to say, making a bubble mid stream that necks back down before the valves is NOT going to increase performance.

Simon 88YJ94XJ said:

If you "hog it out" like he did, not only do you stand a good chance of finding a coolant passage; the very expensive way;

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Actually I didn't remove as much metal as you think I did. In fact the openings in the head are still slightly smaller than the holes in the gasket itself. A minimal amount of material was removed to smooth out the air flow.I also had the machine shop I used check my work before any further machining was done on the head. If there had been, a different head would have been procured and I would've started over.

Yes it is easy to get carried away and a lite touch is needed.

Dang it, no shots of the bowl areas...that is where the easiest increases live.
also, the guide bosses can be knife edged...just leave at least 80 thousandths of meat where the valve stem goes thru...the real danger of grinding ports is in the floor where the port turns to the seat. Never go crazy grinding material out...if you change the shape (flatten the shape), you are screwed....the air will not turn, and the flow will go turbulent at relatively low rpm and the port will flow LESS....there is some flow available in the roof of the port, but you may well hit water jacket, especially if the head has core shift (a very common problem)...the safe way to go is to simply clean and polish all the casting flash and blend the ports..the head flows reasonably well to begin with, especially considering the rpm limitation of the motor.

If you want to see for comparison some really crappy, poor flowing ports, look at a stock 4.2 head..

A gold star to Simon for pointing out the fact that the port cross section is in fact a venturi....it is important to maintain velocity thru the neck area between the runner and the bowl area.

MudDawg said:

Dang it, no shots of the bowl areas...that is where the easiest increases live.
also, the guide bosses can be knife edged...just leave at least 80 thousandths of meat where the valve stem goes thru...the real danger of grinding ports is in the floor where the port turns to the seat. Never go crazy grinding material out...if you change the shape (flatten the shape), you are screwed....the air will not turn, and the flow will go turbulent at relatively low rpm and the port will flow LESS....there is some flow available in the roof of the port, but you may well hit water jacket, especially if the head has core shift (a very common problem)...the safe way to go is to simply clean and polish all the casting flash and blend the ports..the head flows reasonably well to begin with, especially considering the rpm limitation of the motor.

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That's exactly what my machine shop told me before I started working on mine. I stayed away from the guide bosses. The floor of the ports were barely touched with a fine grit sanding drum and a little bit of emery cloth pulled back and forth to smooth out the rough spots.

Frank Z said:

Actually I didn't remove as much metal as you think I did. In fact the openings in the head are still slightly smaller than the holes in the gasket itself. A minimal amount of material was removed to smooth out the air flow.I also had the machine shop I used check my work before any further machining was done on the head. If there had been, a different head would have been procured and I would've started over.

Yes it is easy to get carried away and a lite touch is needed.

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I'll take your word for it, the pics make it look more hogged out than reality I guess, but it does look like you went to town on it

The flash really brightens up the bare metal. I went out to the garage this morning and put the gasket on the side of the head for 93rd time eeks1: ) and all's well.

There is some good literature on porting heads...porting has become a moot point for the most popular engines (Ford/Chevy) because it is cheaper to simply replace the heads with aftermarket ones that have better flow than you can get from a full gonzo stock head...One of the ones I remember the best was one of Smokey Yunick's powerbooks on the SBC..

When I ported the head for the mighty 2.5, it got D-shape exhaust ports and quite a bit of flow bench time...on my 30 year old home made flow bench.

MudDawg said:

There is some good literature on porting heads...porting has become a moot point for the most popular engines (Ford/Chevy) because it is cheaper to simply replace the heads with aftermarket ones that have better flow than you can get from a full gonzo stock head...One of the ones I remember the best was one of Smokey Yunick's powerbooks on the SBC..

When I ported the head for the mighty 2.5, it got D-shape exhaust ports and quite a bit of flow bench time...on my 30 year old home made flow bench.

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Okay I'll bite, how do you make your own flow bench? I'd love to do that, I'd be able to port the head that's going on my YJ's stroker.

It involves an industrial vacuum cleaner head, a bench with various adapters, a u-tube manometer, pitot tube, wet bulb and dry bulb thermometers, an accurate barometer, a dial gauge, a few springs, a dead stop, a psychometric chart, a calculator, a thick pad of paper and a lot of reading up on how to work the various readings into useful info.

No, it's not as accurate as a modern digitally monitored system with 4 color graphics....but it has served it's purpose...the comparative numbers tell you which direction you are heading...and provide fairly accurate flow numbers.

I built it to use on motorcyle heads, but it has enough capacity to be useful on my jeep heads.

MudDawg said:

It involves an industrial vacuum cleaner head, a bench with various adapters, a u-tube manometer, pitot tube, wet bulb and dry bulb thermometers, an accurate barometer, a dial gauge, a few springs, a dead stop, a psychometric chart, a calculator, a thick pad of paper and a lot of reading up on how to work the various readings into useful info.

No, it's not as accurate as a modern digitally monitored system with 4 color graphics....but it has served it's purpose...the comparative numbers tell you which direction you are heading...and provide fairly accurate flow numbers.

I built it to use on motorcyle heads, but it has enough capacity to be useful on my jeep heads.

Click to expand...

Interesting. Got instructions? I've been thinking about doing something like that myself for some time now...

5-90