Porting finish smoothness

[bmwmaster]

Hi all,

actually Im porting an old m20 2.0l head an right now i have nearly finished the port shape to 90%. The rest would be done after cutting seats for bigger valves.

Until now I cutted with my aluminium cutter and the finish has a kind of dimple style structure.
In the past I used to smooth this structure with 120 grid.

Would it maybe be better to leave the rough structue for the dimple style golfball effect and better flow?

Whats yours optinion? experience?

[The Radius Kid]

I would leave it alone.

[bmwmaster]

ok, I also now have an idea to blast it with glass to make the edges round.........wilkl give it a try an make a pic of it

[mag2555]

My routine with Intake ports is to ruff grind them within .030" of the size I am looking for, them polish them out with a 120 cartridge just enough to confirm that all the shape transistions take place in a smooth fashion and then go back in with a Burr and add the texture back.

[RevTheory]

My routine with Intake ports is to ruff grind them within .030" of the size I am looking for, them polish them out with a 120 cartridge just enough to confirm that all the shape transistions take place in a smooth fashion and then go back in with a Burr and add the texture back.

Interesting methodology. Makes sense to me.

[Dave Koehler]

I realize the dimple effect is all the rage this decade but I see no reference to how the intakes being dimpled.
Are the manifolds being ignored or does the magic only begin at the head intake port?
Anyone have dimpled Tunnel Rams or others?
If so is there any quantifiable results from this practice?

[Frankshaft]

I would smooth it out some. For no other reason to straighten everything out, and blend all the transitions better. It looks like it could use that. My take on the aggressive rough finish, is, if the intake runner is on the small side for the engine, its a negative. If its correctly sized, it won't help, and if its bigger than it needs to be, it will help some. I have done some testing back to back, and that's what I have seen. I have one last test to try, a BBC with 12 degree spread ports, na, single carb, cast manifold that makes in the ball park of 1300hp. Currently the ports are aggressive cutter finished. Its going on the dyno again next week to see what a few new changes made. More compression, thinner rings, different camshaft and stiffer pushrods, 7/16 .165 wall weren't stiff enough, and a few other things, a few headers to try, bigger tubes and collectors, also a merge, a few things on the intake and fuel side of things. Then we are racing next weekend, and the engine is coming back out, to do some more stuff, one of the planned changes is removing the rough finish.

As far as the intake manifold, The stupid aggressive rough finish everywhere is wrong. Floor and sides of the port walls can be rough, but anywhere the air and fuel mix turn, as in plenum to runner radiuses, needs to be smooth. The Rough finish everywhere, does the opposite of what most think, the idea that the rough finish atomizes the fuel better. If your carb works properly, and is tuned well, it should be atomized. The rough finish peels the fuel out of the air.

[Carnut1]

I would smooth it out some. For no other reason to straighten everything out, and blend all the transitions better. It looks like it could use that. My take on the aggressive rough finish, is, if the intake runner is on the small side for the engine, its a negative. If its correctly sized, it won't help, and if its bigger than it needs to be, it will help some. I have done some testing back to back, and that's what I have seen. I have one last test to try, a BBC with 12 degree spread ports, na, single carb, cast manifold that makes in the ball park of 1300hp. Currently the ports are aggressive cutter finished. Its going on the dyno again next week to see what a few new changes made. More compression, thinner rings, different camshaft and stiffer pushrods, 7/16 .165 wall weren't stiff enough, and a few other things, a few headers to try, bigger tubes and collectors, also a merge, a few things on the intake and fuel side of things. Then we are racing next weekend, and the engine is coming back out, to do some more stuff, one of the planned changes is removing the rough finish.

As far as the intake manifold, The stupid aggressive rough finish everywhere is wrong. Floor and sides of the port walls can be rough, but anywhere the air and fuel mix turn, as in plenum to runner radiuses, needs to be smooth. The Rough finish everywhere, does the opposite of what most think, the idea that the rough finish atomizes the fuel better. If your carb works properly, and is tuned well, it should be atomized. The rough finish peels the fuel out of the air.

20180503_194630.jpg

Shaft, I agree with what you are saying here. Now my question for you is do you think the surface texture is too rough on this vic jr. tall that will have a t.b.i. system type injection system? I think it is about right due to t.b.i. systems having puddling issues. Thanks, and I look foward to your testing results. Charlie

[swampbuggy]

Frankshaft.....i also will be very interested in what your R & D shows, and THANKS for all your efforts on this subject matter. I for one am VERY appreciative for your willingness to take the time to try and figure out the facts. Mark H.

[Erland Cox]

I believe in a rough finish except where surface velocity is high.
So inner turns should be smothened as the high velocity thins the boundary layer so the rough surface will slow the flow.
But where the velocity is lower the rough texture will activate the boundary layer and make it thinner.

Erland