Porting manifolds question? How to?

[TdiRacing]

I have a set of PMO manifolds, well they look just like them, a few years old, so not sure if they are real PMO ones. Anyway, I have opened my intake ports up a few mm and need to match port the intake manifolds now.

Center is super easy, but the outside runners are not a straight shot. Any tips on porting these.

Was thinking of using specific diameter flapper sanding wheels and porting them that way. Theyshould stay round and I can control the angles. Any other options to get the bulk material cut away?

Do not want to spend the money for extrude honing, so will need a DIY at home way and milling will give an improper taper i believe.

Thanks again.

[jpnovak]

I use a cheap set of rotary files from HF. They are a few bucks for a set of 4 in different shapes. Then I chuck them in a drill (not battery powered) and start milling. This will remove the bulk material and you can finish with a flap or rotary sanding setup on a die-grinder.

[Henry Schmidt]

Matching the manifolds to the ports is not all that important.
As long as the port in the head is larger than the manifold your good to go. There is a school of thought that suggests the use of a 2 mm transition actually improves low rpm performance in carbureted engines.

[TdiRacing]

Originally Posted by Henry Schmidt

Matching the manifolds to the ports is not all that important.
As long as the port in the head is larger than the manifold your good to go. There is a school of thought that suggests the use of a 2 mm transition actually improves low rpm performance in carbureted engines.

Yeah I night just leave them alone and see how it goes. Will be using EFI running TWM bodies, so not sure if that will have any effect.

[911pcars]

Paint the manifold mounted surface with machinist blue, then scribe the larger diameter using the appropriate gasket as a template.

I use Jamie's (JPNovak) method on a drill press. Moving the manifold by hand relative to a stationary tool is a lot more precise than hand holding a high speed cutter and grinder.




An add'l DIY tip: Use a piece of cardboard the size of your target port size, then run a short length of wire through it for a handle (or equivalent) to help visualize the shape and amount of port material to remove.

Not sure the many hundreds Extrude-Hone charges is worth it for the relatively short length of these intake manifolds.

Sherwood

[joetiii]

Originally Posted by Henry Schmidt

Matching the manifolds to the ports is not all that important.
As long as the port in the head is larger than the manifold your good to go. There is a school of thought that suggests the use of a 2 mm transition actually improves low rpm performance in carbureted engines.

Henry,

How about if one is going beyond a few millimeters. Say as an example, I've currently got small port SC heads with the smaller PMO intakes at 34mm. I go to a 40 mm 3.2 head? Is the 34mm manifold too restrictive then?

The rest of the upgrade is designed around a hot street/ autox setup with DC40 or GT2 Cam, 9.5 95 mm JE's, & possibly twin plug.

[Henry Schmidt]

We are using a new port design that affords us the velocity of a small diameter port and the flow of a large port.
We are generating 310 hp @ 7200 with 95 mm bore, 70.4 mm stroke ,10.5:1 comp., twin plug and MFI with 1 5/8" headers. 310 hp 3.0 through a 36mm port.
For us, the days of large ports ( 43mm intake RSR nonsense) on early 911 engines is over.
Large ports only make sense on a large 8000 rpm engine and even at that, 41mm is the max. That number can go up if larger valves are employed.

[TdiRacing]

I have measured my manifolds and heads and I was completely turned around on what I needed to do. Long time since I looked at the stuff. I opened the heads slightly to match the manifolds. Ports are 34.5mm on the intake side. So have 40-34.5 manifolds as pictured below. So I just need to clean the heads up slightly from the machining and send them off to get finished.