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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
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Wouldn't it have been easier to have a machinist mill that port down to the bend?
Are you using a bore gauge to keep the ports round as you go?
Are you going to get the heads flowed when your done? Would be nice to know that the mass flow into each cylinder is somewhat equal.
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Old 05-20-2013, 03:27 AM
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You are a brave man. I've always thought of head porting as wizardry.
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Old 05-20-2013, 05:01 AM
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Quote:
Originally Posted by 911nut View Post
Wouldn't it have been easier to have a machinist mill that port down to the bend?
Are you using a bore gauge to keep the ports round as you go?
Are you going to get the heads flowed when your done? Would be nice to know that the mass flow into each cylinder is somewhat equal.
Yes, it would have been easier to take them 25 miles up the road to xtreme cylinder heads and have Bill do them but thats expensive and I have more time than money and I'm really good at doing this by hand. I have very good eye-hand mechanical skills and I've done it many times on other cars and motorcycles with great success.

I don't have a bore gauge, I use a digital micrometer to measure and then I mount my 40mm aluminum injector blocks on the heads and use a sharpie pen to draw a back circle and a machinest scribe to mark the port matching 40mm circle I'll hog them out to.
The rest I do very carefully by eye and feeling the inside of the ports with my fingers. Kind of like doing body work on cars and block sanding the fiberglass and body filler to get it shaped perfect and I've done tons of that too.
If you know what you're doing, you have a good eye, and know where not to take too much material off > like the short side radius then you can do a good job by hand.
I will be doing the intake manifold ports the same way. I wish I had another CIS intake manifold so I could do that now and have it ready to install along with all the other parts but I only have one intake manifold and I'm still driving the car right now.

I'm not going to take any material out of the bowls.. they're big enough already but I will sand away and blend/smooth the crude casting marks along the sides and radius and smooth the origonal semi crude rough edged machining done by Porsche all the way around about 8-13mm before the valve seats.

These are 1976 930 heads and I was hesitant to do this because the value of '76 930's seems to be going up so the origonal parts from them would be too.. but I have these already and the the exhaust valve guides in my '87 930 are worn even though they only have around 40,000 miles on them since the previous owner had the top end rebuilt so it makes $ sense to me to do this. These heads have new valve guides installed and fitted correctly and a fresh valve job done to them already with new exhaust valves.

The '76 930 is 95mm bore and my '87 is 97mm bore. To use these '76 heads I had to have a 1mm wide bevel cut into the edge of the 95mm combustion chambers or else the inner edge of the sealing surface would become a sharp edged 1mm squish band. Sharp edges in a combustion chamber run hotter and that could cause detonation and the pistons might hit it.
I took these heads up to Xtreme cylinder heads and Bill cut the 1mm wide bevel into them a few months ago.

On another note, I have an old '75 BMW R90S motorcycle I bored out to 980 CC and installed new R100/7 pistons in way back in 1988. Those hemi combustion chambers are very similar to 911 heads.
Instead of paying someone else I made the same type of bevel in the edge of the squish band by hand with a round sided metal file, then hand sanded it smooth, polished the combustion chambers and it worked out perfect.
I didn't want to do that on six 930 turbo heads so I had Bill at Xtreme do that on a machine.

When I finish these ports I'll take pics of them. I won't be done and satisfied with them until they look as nice as any other hand finished ports I've seen pictures of.

Last edited by JFairman; 05-20-2013 at 07:02 AM..
Old 05-20-2013, 06:58 AM
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Quote:
Originally Posted by JFairman View Post
Yes, it would have been easier to take them 25 miles up the road to xtreme cylinder heads and have Bill do them but thats expensive and I have more time than money and I'm really good at doing this by hand.

I don't have a bore gauge, I use a digital micrometer to measure and then I mount my 40mm aluminum injector blocks on the heads and use a sharpie pen to draw a back circle and a machinest scribe to mark the port matching 40mm circle I'll hog them out to.
What I meant was to have the vertical portion milled and then finish the transition by hand to save time.
A bore gauge will allow you to reach deep into the port and check roundness and diameter. Are your mics the long type?
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Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, - 210 lb
Old 05-20-2013, 07:23 AM
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I know what you meant.

I have 8" mitotoyo vernier dial calipers and harbor freight 6" digital calipers that work just as well and are easier to read quickly.
They don't reach into the port so I use a small 90 degree square edge I put against the gasket surface and into the port and rotate it around to visually see if more material has to come off anywhere along the sides.

It's only around 1.5" into the port that you remove material. The rest I'll be doing is blending and smoothing. I put a piece of fuel line over the valve guide to protect it and layers of masking tape on the valve seats to protect them while grinding or sanding near those parts.

I'd get back on it today but it's raining now...
Old 05-20-2013, 07:39 AM
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Quote:
Originally Posted by JFairman View Post
I wish I had another CIS intake manifold so I could do that now and have it ready to install along with all the other parts but I only have one intake manifold and I'm still driving the car right now.
I've got a couple laying around I could make you a deal on. What are they worth?
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Old 05-20-2013, 08:44 AM
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I've got a couple laying around I could make you a deal on. What are they worth?
That sounds kinda interesting but I really don't need to be spending more money on this progect while I'm going into the slow summer season for my photography work around here.
It's proabably one afternoon of grinding and sanding to enlarge and match the 6 intake manifold holes to my 40mm injector blocks so I'll probably just use the manifold thats on my car now.

That said, if you wanted to sell one cheap I'd think about it. Then after I install this stuff I'd try to sell mine cheap just to get rid of it afterwards.
Old 05-20-2013, 09:44 AM
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I like it, keep on posting.
I intend doing the same. Certainly the price is right and the results are truly yours.
Old 05-20-2013, 04:05 PM
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Thanks copbait I will.
Only unpleasent thing is I won't be walking by that part of my driveway barefoot for a while

Old 05-20-2013, 04:18 PM
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