porting heads...

[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.

[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.

[ericjon262]

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

[SappySE107]

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

[Superdave]

2

[SappySE107]

Care to guess how many CFM that is worth?

[TGP37]

Yeah? Must be nice to have flowbench vision.

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

[Superdave]

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

[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?

[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.

[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.

[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]

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

[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.

[ericjon262]

One issue is 2 ports are 30 degrees offset from the other. Atleast it is 15 degrees either way for the 3100 aluminum heads exhaust port. And you would need to reverse the movement from the primary. And the pockets are placed where the exhaust valve is outside on both ends. Making linear replication near impossible.


I think a caliper, shop vac and LOTS of light will do much more. I know you can bring each port to a closer spec by hand.

I sculpted many "little" statues and did all sorts of artistic work over the years. Your hands can form precision, it just takes patience and practice.

If you smoke or not, a good cigar hanging in the air helps calm the nerves and steadies the hand.

I would do the first port by hand, and then use the pantograph to duplicate it, I haven't figured out how to reverse it yet for the ports that don't line up. It would get used more than once, not just on a set of 3500 heads, I've got some 302 heads, some Lt1 heads, some 305 tune port heads ect...