Home porting, where are the key areas?

[Datsunboy]

Guys, when my heads get pulled, they will be ported by me. Question I had was, where are the favorite spots to remove material? I dont have a ton of time to port, and i would LIKE to get the heads done in one (long) day. Im not so interested in going overkill but am confident in doing it myself.

Also, dont have time to wait for the standard abrasives kit to arrive. What can i use? I have a dremel tool with all the trimmings, and an air grinder.

Thanks gents - Evan

 

[Crazi]

Here's what I did. I cleaned up the ports as much as possible meaning make them smooth. They generally have a lot of casting flash and dimples. The I cleaned the guides up a little and removed the ridge above the valves. Basically, use your finger as a guide. If it feels rough, keep smoothing.

I hear that the short side radius and the bowl area is where the work should be concentrated. Work on all intakes on one head at a time then do all exhausts. Try to do the exact same thing to each one unless you are going to put it on a flow bench. For the exhaust, I cleaned up the valve guide and again, made it smooth.

You should also port match it if you can. Check out Standard Abrasives website. They have a REALLY good tutorial.

 

[Datsunboy]

Standard abrasives tutorial is excellent, thanks for the reference.

Sounds good though, if i do go to the trouble of porting thats probabally what I will do.

I may skip the porting, im still kinda dissapointed about this whole situation with needing a valve job, and not being ready. I really SHOULD port the heads, but downtime on a daily driver really sucks ass.

Thanks dude - Evan

 

[BM Computer Src]

I ported my heads with a dremel. It took a while because the Dremel isnt really able to move enough material fast, but results were well worth it. Follow the Standard abrasaves manual and you will be fine, it's what I did. I wrote up mine, step by step.

www.bmcomputersource.com/heads/heads.html


Hope this helps and please let me know if you have any questions.

Bob

 

[UNGN]

The best way to port a set of heads is start with a 3 angle valve job with a deep throat cut. Just a hour of blending in a 3 angle valve job will flow more air than 5 hours of smoothing and polishing the ports. An un-blended 3 angle valve job will flow about 5% more than a stock head without one. That could be 20 Hp on a 400HP car. Not bad for $100-150.

From there, you want a smooth transition from the cast surfaces into the machined areas. A good short side radius and make sure the walls blend smoothly into the throat cut. Smooth and reduce the valve guides so the air will flow around to the back side of the intake valve. Make the exhaust guides as small as you can, with whats left providing a smooth channel for air to go around the valve stem. Cylindrical shapes have 10 times the aerodynamic drag of an airfoil shape with the same cross-sectional area. Using the guides (both intake and exhaust) as a fairing will increase the airflow velocity by making the stem shape more of an airfoil and less of a cylinder.

Avoid blending on the port floor out from the short side radius. The higher the ports the more air they will flow. Lowering on the port floors can actually reduce airflow through the valve throat area. Ideally, the intake port floor should be raised a quarter inch or so, but adding material is hard to do with a die grinder. Smooth it and remove large casting flash, but take a minimum of material off. Instead, make sure the roof of the port is smooth and if you are going to gasket match take the top of each port to gasket size (leave the bottom alone).

Smooth and radius the "pushrod pinch" on the intake port, but don't remove too much material or you will ruin the head.

Have the stock valves "back cut" while the 3 angle valve job is being preformed. This will remove the ridge at the valve seat and the valve will flow more air at low lifts. Many performance machine shops will do this very cheaply and the result will flow comparable to aftermarket stainless valves (that are manufactured without the ridge) especailly at the low lifts our cams run.

The best tool to port with is doublecut carbide burrs. they are relatively expensive, but can last a very long time. They will cut through cast iron like butter, so you have to use caution. After everything has been roughed to shape, sandpape rolls do a good job smoothing.

 

[Crazi]

Damn, I might just go back through my heads and do some of the stuff ungn mentioned.

 

[Datsunboy]

wow thanks for the good information guys.

Is it okay to have a valve job performed and THEN port the heads? I noticed that blending in the 3way is the key. I would prefer to have them hottanked only one time as well.

Thanks guys - evan

 

[KendallF]

You would probably be better off to do the majority of your port work before the valve job and perhaps blend the bottom cut into the bowl afterwards. It only takes one nick with the die grinder to ruin that new valve job.

UNGN's given some good advice..all the casting removal in the ports looks pretty but isn't worth much compared to the bowl work.

I'm sure not an expert but I've done a few sets and at least they aren't running slower than stock. Some pics of my first effort at head porting are on gnttype:

http://www.gnttype.org/techarea/pictureguides/heads/porting/porting.html

Here's a pic of a later effort (the heads that are on my GN now):

http://photos.yahoo.com/bc/frederik...block+motor&.src=ph&.dnm=Dscf0008.jpg&.view=t

It may be hard to tell from the two photos but the on the later set I opened the bowl area up more.

One final word of advice: if you are going to do them, chuck the Dremel and go buy a 1/4" shank die grinder, whether it's air or electric, and some carbide bits. Otherwise you may be eligible for AARP before they're done.

 

[The Radius Kid]

Port,then valve job.One slip working in the area of the seat and............

 

[Crazi]

That's what I mean. Go porting again and then go get a three angle vs. a standard valve job.

 

[dpok69]

I dont know if im on the same topic or not, but does the gn1 heads have all these porting and valve work already done on it?

Or is it more economical for a novice like me to bring my car to the shop and have them do all the work?

 

[UNGN]

I've done them both ways. For someone who has done a few heads, it takes less time to do smooth/polish the chambers (with junk valves protecting the seats), Maybe do the pockets near the guides, then do the valve job, then carefully port the rest of the head, then go back to the machine shop and face the mating surfaces (and touch up any seats you may have nicked).

The valve job removes a lot of material that you may not remove if you port first, so you'll need to go back and blend it in, anyway. A steady hand, lots of patients and good cutters help.

As note by kendall and others, its very easy to screw a head up.

 

[Ellis]

This is a good topic for me, since my heads are on the workbench right now, getting ported a little at a atime as I can get at it. It's nice to see that the approach I was taking is so far right on.

I do have a question: I plan on using stock sized back-cut valves. Aside from polishing the combustion chamber, should anything there be reshaped? Mostly I keep looking at the hard parting line as the chamber transitions into the machined surface on the bottom of the head. Is this sharp point a hot spot?

 

[UNGN]

I smoothed out the chamber surface (not to a high polish like some do, because thats a lot of work ) using a cutter first on the really rough stuff and a flapper wheel on the rest. With some junk valves protecting the seats. Then I sent the heads off to the machine shop to be milled flat. They took .006" off the surface and completely removed the nicks that may have occured during the chamber work. Then I carefully went back with a carbide cutter and broke the sharp edge. That's pretty nerve racking as the heads are completely done at that point, so its a good idea to lay off the caffeine before you do it. The only thing harder on the nerves than this is blending in the bowls after the 3 angle valve job or removing the valve spotface ridge in the chamber.