porting heads...

[Superdave]

IMO, that'll just take way too much time for the little bit of port work you'll be doing. I can see maybe something like that for a full on re-shape but even with the hours and hours into my intake ports it's easy enough to duplicate by sight/feel/memory.


Just go in there and cleanup the casting flaws (there aren't many), blend the area just past the valve seat, sand the exhaust ports to 120 grit, Crossbuff and that's about it. You aren't going to remove very much material at all.. probably a tablespoon sized pile per head at the most with the carbide cutter.

[TGP37]

IMO, that'll just take way too much time for the little bit of port work you'll be doing. I can see maybe something like that for a full on re-shape but even with the hours and hours into my intake ports it's easy enough to duplicate by sight/feel/memory.


Just go in there and cleanup the casting flaws (there aren't many), blend the area just past the valve seat, sand the exhaust ports to 120 grit, Crossbuff and that's about it. You aren't going to remove very much material at all.. probably a tablespoon sized pile per head at the most with the carbide cutter.

+1

[ericjon262]

well guys, I'm getting a cam for my 3500, and am kinda reconsidering porting the heads because the cam swap will have it down to the block and heads, and it would be a good excuse to put a better head gasket in. is the work going to be worth the gains? You'll are talking about removing a very small amount of matieral, which to me sounds like there isn't much to be gained.?

[TGP37]

The gains are proportional to the work done. If you manage to achieve a good port job, you should feel the difference easily.

Once you get the heads off and the valves off, you will see exactly what needs to be ground down. Your not going to reshape the pocket, just remove the flaws and give a nice texture on the walls.

Put duct tape on your valve seats but allow the space to blend the back half. It may save the seal if your carbide jumps and grazes the seats.

A shop vac and lots of light is a must.....you don't want to breath aluminum flakes.

[SappySE107]

Once you get the heads off and the valves off, you will see exactly what needs to be ground down.

Yeah? Must be nice to have flowbench vision.

[ericjon262]

well, me and a buddy have been talking about building a flowbench anyways, so maybe there's no time like the present? anyone know of a good kit? or am I on my own for that?

[Superdave]

When i built mine i used a lot of info from here: http://www.flowbenchtech.com/

[TGP37]

Yeah? Must be nice to have flowbench vision.

haha, funny. I meant the casting flaws, those seems running up each side.

[SappySE107]

Care to guess how many CFM that is worth?

[Superdave]

2

[SappySE107]

Maybe on the very worst cast 3500 GM ever produced:P

[ericjon262]

do you guys think it's worth it to do a port job on it?

[3400-95-Modified]

So after reading all of this porting 3500 head is useless and you'll never improve what GM did? Damn I never thought I would hear that one.

I just got a new set of heads and LIM that I'll probably be revisiting... Not sure what I'll do this time but we'll see.

[SappySE107]

So after reading all of this porting 3500 head is useless and you'll never improve what GM did? Damn I never thought I would hear that one.

I just got a new set of heads and LIM that I'll probably be revisiting... Not sure what I'll do this time but we'll see.

I can improve 3500 heads.

[geoffinbc]

Of course you can improve them. Is a flow bench required to do so? Of course not. Does it help optimize results? Well obviously it does. However, all as cast heads respond well to gasket matching, bowl blending and valve guide profiling. You don't need a flow bench to do it but you should at least be measuring the work you do so you can get each port the same. The easy way to do it is get a set of locking telescopic gauges and use them as a go/no go feeler gauge. Working with a good machinist or having a milling machine is a great start because it can establish the size of the port behind the valve. The actual desired size is going to depend on application but there are lots of formulas and recommendations out there that will give you a size based on the percentage of the valve diameter. At the very least clean it up so it is concentric. If you never use a bench to flow your heads you will not have a CFM number you can put on them and you will not know the before and after difference. Knowing this will allow you to come up with an approximate horsepower difference. None of this is a requirement by any means but it is useful data.

Modern castings are pretty damn good so you may not have much work to do. When I went to work on my iron heads it was a different story because the casting flaws and bad transitions are blatantly obvious. All I did were the basics along with gasket matching the intake manifold. I never adjusted the shape of the port I just smoothed it all out. I followed some of the tips I read in Engine Masters magazine where they did work on a Chrysler Magnum head which has very similar port flaws as my iron heads. Their CFM results were impressive with just some simple clean up techniques. When I get a bigger garage I am going to build the same bench that David Vizard recommends in his magazine. The cost is around $150