Head Porting Fun

[a930pilot]

Since I'm going to use the Carrera Intake on my EFI build, I wanted to get a set of heads ready and on the shelf. Here is a quick summary:

Step 1 - Weld Intake surface of the heads


Step 2 - Machine to create the intake gasket surface


Step 3 - Using a boring bar on the mill, I ported in a couple of steps to a max depth of 1.25". The rough steps was supposed to make the hand blending easier. It didn't seem that way.


Step 4 - After blending the ports by hand with a carbide burr.


Step 5 - Ship to Craig Garrett who twin-plugged them and machined for knock sensor bars, grind valves & seats, then rebuilt with DRC springs and Ti retainers. He's a great guy to work with and fantastic pricing!!

[Tippy]

Very nice! Did you maintain the 41.5mm down the intake port?

[JFairman]

They look good for the first inch or so into the port. Then there's room for improvement that has to be done by hand with porting sand paper rolls on an arbor fitted to a die grinder.

Or for the best cylinder head porting on the planet send them to Bill at xtreme cylinder heads and have them done entirely on a very expensive head porting CNC machine. No hand porting is done that way.
You can watch video's of it being done on his website.

I would smooth and blend the mark that looks like a ridge in the port where the milling stopped an inch or so into the port and then smooth the rest of the port and the entire bowl around the valve guides and up to the valve seat by hand for a possible small flow improvement.

[a930pilot]

Cory,
Probably not all the way down. If I recall, I did 40mm to 1.25 inches and 41mm to 1 inch.
There was still a lot of blending needed, so I'm not sure what the final dimension was down near the valve. Frankly, I got bored working with the die grinder.
It is amazing comparing the stock ports with the 3.2 port size. These look massive and the stock heads just look small!

[a930pilot]

I agree that there is room for improvement. There was additional sanding done with paper rolls and cross buffs after I was done with the burr. I just smoothed the surfaces up near the valve.

While I'm sure that Bill has great heads, this was more about DIY. I would rather not pay people to do things I WANT to do myself even if that means mine won't be as good. I will however say that I no longer WANT to do this again. I got it out of my system.

[Tippy]

Originally Posted by a930pilot

Cory,
Probably not all the way down. If I recall, I did 40mm to 1.25 inches and 41mm to 1 inch.
There was still a lot of blending needed, so I'm not sure what the final dimension was down near the valve. Frankly, I got bored working with the die grinder.
It is amazing comparing the stock ports with the 3.2 port size. These look massive and the stock heads just look small!

Yep! Every time I see a stock 930 head, I think how much volume is left on the table.

She's gonna be a beast when done!

[JFairman]

I ported mine in my backyard by eye with carbide burs and sanding rolls on a die grinder. I've done a bunch of 2, 4, and 6 cylinder BMW's and some 912 ports this way in the past and I get satisfaction from it because they all came out nice.

Here's the ones that are on my car now that I ported and they work great.
The valve guides were new so I put little pieces of rubber hose over them to protect them while grinding and sanding around them. The valve seats were also freshly reground so I put layers of tape all over them to protect them too.

I used 40mm CIS aluminum injector blocks and also port matched the 32mm holes in the original intake manifold to 40mm.
The first pic is when I first started opening the holes up from 32mm to around 39mm with a heavily fluted carbide bur that cut away aluminum quickly. You dip the carbide bur into a small container of WD40 every 2 or 3 minutes so the carbide bur doesn't load up with aluminum. If it does you have to pick it out with a machinist scribe. The liqued WD40 is in the small upside down black spray can cap in the picture.

Then switch to a finer burs to smooth things out more while taking them to around 39.8mm and then finish up with the sand paper cones to make them a smooth and nice port matched 40mm inside diameter.

You can get good sand paper cones at Harbor Freight tools but the steel arbors that come with them break quickly so I bought some good arbors in different lengths and the carbide burs from an online tool store.

You want a semi rough surface on the port walls like 80 grit sand paper would leave so the fine fuel mist in the port tumbles over the port wall surface as air flows through it and stays atomized as much as possible..

[billjam]

Ha! I'll buy into this. I just love getting my hands on fresh heads and have done lots of different types over the years, but the principle is always the same, although less critical with forced induction.
My last 930 heads went like this ...