View Single Post
JFairman JFairman is offline
Registered User
Join Date: Jul 2006
Location: S. Florida
Posts: 7,289
Going from 32mm to 40mm intake ports

Started porting a set of 930 heads I bought around 5 years ago today. They had a fresh valve job with new guides when I got them complete with good valves and all the studs.
I've been wanting to port them to 40mm to match a set of 40mm aluminum injector bolcks I got around 4 years ago and decided to have at it today before it gets any hotter down here this coming summer.

I start with this course fluted carbide bur and then switch to a finer one thats around 7" long to reach farther in there to enlarge, smooth, and blend it more. I have some small round ones for small tight areas like around the downstream side of the valve guide.
There were new valve guides in these when I got them so I'm not going to grind and streamline the lump of cast aluminum around the valve guide because that should be done with no valve guide installed if you do that. Doing that has very little air flow gain in a turbo motor anyway and all the 935 heads I've seen leave it there untouched for better heat transfer and strength for the valve guide just like a stock head.

Once I'm done with the carbide burs I'll switch to 60-80 grit sanding cones on an arbor made for porting with a die grinder. I'll finish them off as nice and blended as I can with the sanding cones to leave the surface a little rough for good surface turblance along the port walls to help keep fuel from wetting out on the port walls.
I've done this on many BMW heads so I have experience doing this.

This pic is right at the beginning of doing this port so it's in the rough stage and only part of it is hogged out here.

Old 05-19-2013, 06:34 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)