Head Porting

[4point6]

I am starting to (try) do a port and polish job on the heads. I know you are supposed to gasket match the intake port to the intake manifold. Are you supposed to open up the exhaust port to match the gasket also, or just clean it up? I'm pretty sure you leave the ports in the exhaust manifold holes alone?

[Flash]

I am starting to (try) do a port and polish job on the heads. I know you are supposed to gasket match the intake port to the intake manifold. Are you supposed to open up the exhaust port to match the gasket also, or just clean it up? I'm pretty sure you leave the ports in the exhaust manifold holes alone?

IF the exhaust manifold is larger then the port, let it be..........Especially the floor or the bottom of the port. Grinding on the bottom of the port will actually cause less flow...........
Are you going to pull the valve and port the bowl area too, or just the inlet/ outlet of the port.



Flash.

[oletshot]

What gasket are you using to match the intake ports to? I was also considering massaging the ports myself and bought a felpro gasket (cheapest since I probably would mess it up anyway) to match to. Trouble is, the gasket matched my intake ports already. I didn't want to keep buying gaskets trying to find one that didn't match, that I could grind the ports to.

[4point6]

What gasket are you using to match the intake ports to? I was also considering massaging the ports myself and bought a felpro gasket (cheapest since I probably would mess it up anyway) to match to. Trouble is, the gasket matched my intake ports already. I didn't want to keep buying gaskets trying to find one that didn't match, that I could grind the ports to.

I am going to use Victor, but I haven't gotten the gaskets yet - they are being shipped. I'll let you know when I get them. I checked the original gasket (stock), it is pretty close but there is a little room to open them up on intake side. Exhaust is a different story - there must be 1/8" between the port and the edge of gasket that could be cleaned up, but I'm not sure if I should match that one. From Flash's response it looks like no.

[Flash]

What gasket are you using to match the intake ports to? I was also considering massaging the ports myself and bought a felpro gasket (cheapest since I probably would mess it up anyway) to match to. Trouble is, the gasket matched my intake ports already. I didn't want to keep buying gaskets trying to find one that didn't match, that I could grind the ports to.

I am going to use Victor, but I haven't gotten the gaskets yet - they are being shipped. I'll let you know when I get them. I checked the original gasket (stock), it is pretty close but there is a little room to open them up on intake side. Exhaust is a different story - there must be 1/8" between the port and the edge of gasket that could be cleaned up, but I'm not sure if I should match that one. From Flash's response it looks like no.

Removing a sharp edge and bevel is fine, just don't try smooth it in a Half of inch inward

If the ext manifold is larger then the heads ext port, there is noting to slow the flow down just leave it as is. the intake you want to make the intake manifold and intake port match the gasket.

flash.

[Muad'Dib]

Seems like this belongs in the advanced tech section since its not necessarily related to a stroker... i hope others agree.

[1bolt]

Warning long:

Most will tell you to just clean up any casting irregularities and knife edge the valve guide boss blend that work and be done with it leaving the exhaust mostly alone (except knife edging). I think that's sound advice.... if you are going to dig in more than that read on.

Okay first off you should know that you can absolutely kill your air velocity and low to mid lift flow numbers by doing even small minor wrong changes. What's a wrong change? well you'll need a flow bench and velocity probe to truly tell. I don't have such a setup so you can say I'm talking out my ass and I couldn't argue; but the only scientific 4.0 specific porting I've read about backs it up.

Gasket match carefully The 4.0 gasket depending on year of the head and gasket is as much as an 8th inch away from the opening on both the intake manifold and port sides...

That's a 99+ intake a 99+ cometic style gasket and an 0331 head. As you can see there's a LOT of material that could be removed. Especially on the intake side... The intake runners are smaller than the port runners, to promote velocity at lower RPM's.

If you cut an 8th inch all the way around the port and intake and exhaust and blend it back a couple inches on both sides; like this guy:

(can't believe he didn't hit water)
you will not only be close to water on the port side, you will have made a pocket on the intake side that will allow air to expand, turbulize and thus slow down, which will kill your low end torque.

If you gasket match do it in such a way that the cross section (the actual volume of space in any given area) remains the same from the plenum all the way to where the bowl of the valve seat opens up... In other words you either need to increase the intake and port runners to the same size as the gasket match or not remove much.

Dino Savva's got a good short primer on cleaning things up here:
http://www.jeep4.0performance.4mg.com/head.html
One of the only thorough writups of scientific 4.0 head porting is by a guy nicknamed Nosigma, he wrote some articles and a series of posts on his results with a flow bench. On 4.2 and 4.0 heads. He's been on NAXJA and I've collected everything I could find that he wrote. It's highly recomended reading.

There is absolutely nothing else that is scientific and specific to our engines out there that I've found. And I've searched high and low, because this is an old favorite subject . There is lots of generic stuff (the standard abrasives writeup) and SBF and SBC stuff.

[Shark]

would you clean up the protrusions below the fuel injector holes in the intake?

[oletshot]

Ok, with all that said I'm putting the handi-grinder down and stepping away from the bench.
Seriously though, I'm glad I didn't start grinding away because I would have done something similar to what the head in the picture looks like. The drawing really help explain how you could easily do something bad. I remember reading something about not polishing one of the ports as much as the other. I can't remember if it was the exhaust or intake that was supposed to be polished more than the other, nor can I remember why? Anyone else ever hear of this?

[4point6]

Ok, with all that said I'm putting the handi-grinder down and stepping away from the bench.
Seriously though, I'm glad I didn't start grinding away because I would have done something similar to what the head in the picture looks like. The drawing really help explain how you could easily do something bad. I remember reading something about not polishing one of the ports as much as the other. I can't remember if it was the exhaust or intake that was supposed to be polished more than the other, nor can I remember why? Anyone else ever hear of this?

1bolt - thanks for the write up. Like oletshot, I'm rethinking my port matching plan right now. I think at least I will polish and clean up the valve guides.

oletshot - I read that you keep the intake surface a little rough, but the exhaust surface is polished. Check out the standard abrasives guide:

http://www.sa-motorsports.com/diyport.aspx

[whitey2001]

If you cut an 8th inch all the way around the port and intake and exhaust and blend it back a couple inches on both sides; like this guy:

(can't believe he didn't hit water)
you will not only be close to water on the port side, you will have made a pocket on the intake side that will allow air to expand, turbulize and thus slow down, which will kill your low end torque.

Ok, now you guys have got me worried. I have the 2686 casting and I followed the instructions from the porting kit which said to use the gasket as a guide for the port job. On my exhaust ports, I had a large amount (maybe 1/4") that could be feathered to match up with the gasket (like in the pic above). The instructions said to leave the intake ports alone except to remove burrs, imperfections, etc. I did that, but I have to say that my port job is looking similar to this (above). Is it my casting that just looks this way (pockets), becasue I know my intake port walls were not perfectly flat/straight prior to my port job. Does anyone have a picture of their port job on the 2686 casting? I hope I haven't jacked my head up.

[oletshot]

That looks familiar 4point6. That's probably where I read it. Thanks

[John]

"I remember reading something about not polishing one of the ports as much as the other. I can't remember if it was the exhaust or intake that was supposed to be polished more than the other, nor can I remember why? Anyone else ever hear of this?"

Oletshot, polishing the exhaust side reduces carbon build up, and is ok, if you are polishing, remember this is not about removing lots of material. Do not attempt to remove the material on the exhaust side to match to the gasket, the ledge between the head and the exhaust header benefits us by reducing reverse flow of the exhaust gases into the head on the reflected pulse. If you have worked with two stroke expansion chambers, it is a similar concept. The intake runner should not be polished as this will reduce flow at low valve lift. Same reason a golf ball has dimples. Air has a lower coefficient of friction than the surface materials provide. Leave the intake with texture.
John

[1bolt]

I read that you keep the intake surface a little rough, but the exhaust surface is polished.

Yep that is definitely the current thinking... Gale Banks says so and that by itself carries weight with me.. With a "wet" carbureted intake manifold the cast (or rough 80 grit) texture helps fuel suspend and stay off the walls. by promoting a thicker low friction "boundary layer" of air on the walls. In our case, with port fuel injection it is not very important. That's the practical side to the argument. The other side is that "rough" cast or textured surfaces promote higher air velocities due to that same boundary layer effect. So it's even theoretically good for fuel injection.

I'm personally not convinced on the last part... the thicker boundary layer that a rough surface has may help velocity but because it is thicker it is effectively like having a smaller runner cross section. In other words it will flow less volume at the same velocity than a smoother runner might. The other side of the coin it how much roughness is enough? Teflon coated pans are extremely low friction, but they always have a satin texture... I bet that smooth satin texture is pretty optimal.

It's probably one of those diminishing returns trade offs, just like long runner intakes that help torque (through low RPM air velocity) versus very short runners which promote high RPM horse power (by flowing the most CFM) At some point there's a balance where the increase in air speed makes up for the slight loss of effective runner cross section. Through most of the usable power band... Basically a "sweet spot". Finding out where that sweet spot is would take more CAD modeling and reasearch than we can muster here... On the other hand the 99+ intake has not been improved on even by Lee at HESCO who has tried to. So that intake is IMO a very good example of the sweet spot.. According to HESCO It makes as much as 10 extra torque through the powerband while still netting a couple extra HP at peak RPM's...

[John]

Not polishing does not mean do not smooth out. I polish my exhaust ports, looks mirror like and I smooth my intake ports, you feel the texture with your finger easily, but they do not look rough.
John