Thread: Basic Head Porting Tips

Always remember, the limits until breaking into water are not nearly as important as velocity. 9 times out of ten, if you push that far, you're going backwards in power. I get guys with, say XP or S1x cams who want all- out ported heads. The heads I port them won't flow as much as a ZZP or Intense stage 3 or 4 head.

But those heads see max flow at around 600 lift Where an XP or an S1x is only between 520-540.

Porting strictly for velocity can make a pair of heads out-flow the big boys at 550 lift and below where it matters for a smaller cam.

If you don't have a tight enough minimum cross section, you will need more lift and RPM to see the benefits of all your extra work.

Velocity comes first and you never want to sacrifice any of it for volume.

Port shape is also extremely important. It might seem right to squeeze the flow for the highest velocity at the port, but if you don't accommodate the short turn your gonna try to shoot all that high speed air out of one side of the seat. Ideally you want to slow the velocity around the short turn to allow the air to flow equally around the seat.

I agree about port shape being important, but velocity over everything at all cost. Your port shape, tapering, short turns, valve job, guide work, surfaces, bowl blending, hips and roof wall should all be going after velocity.

If you shoot the air unevenly out the seat, but get more air in the cylinder, you still make more power. Also, the piston draws air straight down during the induction stroke. The fact that the intake seat is offset from the center of the bore makes the air flow favor one side unevenly anyway. The portwork should comprimise with the stroke direction becase that's a fixed variable.

"Your port shape, tapering, short turns, valve job, guide work, surfaces, bowl blending, hips and roof wall should all be going after velocity."

Everything I've underlined IS primarily what makes shape, lol. I'm pretty new to this so don't think I'm debating lol. I learned from your videos and I really appreciate them. I just enjoy reading about this stuff and trying to get my mind around the flow of air through an engine.

Point I was making is that you can't focus on just one aspect of it. Just as you were saying its not ALL about volume, I thinkbyou can also fairly say its not ALL about velocity. It seems controlling the movement of air through the runner is what the pros try to do. They go to great lengths trying to get the air to stick to the short turn, including ADDING material to the floor. Somewhere I read that the ST radius would need to be around 4" to get optimal control over it. Since that is not feasible, they will allow the port to expand around the valve seat area, before it constricts again through the valve. This allows the air to slow a little and hug the ST more, which allows it to utilize more of the valve opening.

Regardless, its all very fascinating. Just wish I had a hundred sets of heads and a nice flow bench to see it all for myself

Ok I get what you're saying & very glad I could help. First let me apologize if it seemed like I was trying to debate or argue. I want people to get the clear cut truth. (At least about these heads)

saw these on ebay....you can see where most of the work on the exhaust port should be on the port roof to extend the radius of the port bend to transition to the perpendicular header tube from the OEM 30* exit angle.

http://www.ebay.com/itm/Buick-3800-S...03cba1&vxp=mtr