924Board.org

[Raceboy]

It's not for 924 unfortunately, I did it for my 911 heads. Opening up the ports of 911 T heads (32 I/32 E) to 40 mm intake and 37 mm exhaust.

I have 4 axle Heidenhain CNC milling machine at my disposal but of course not too experienced working on it. Getting better by the day though. Main objective is not get familiar with CNC machine per se but to fabricate and modify parts

Few pics:




Finished both intake and exhaust machining yesterday and need to finish the transitions with a burr. After that I'll drill 2nd plug holes too.

Main benefit using CNC machine is that ports are all equal and of course it takes much less time than machining every ports by hand.
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche

[!tom]

Drool!
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78 924 NA
5-lug

[flosho]

I'm boxing up my spare 931 cylinder head. Have at 'er.
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[This Space For Rent]

[Martijnus]

so the thing I don't understand with CNC is that you already have a (semi)product... machining it with CNC means that you need to make a reference, right?

You can't just throw a head on the machine and let the computer figure out where the original port is.... so how do you do that?
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"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[Min]

[Raceboy]

I wrote a simple program that makes a circle, specified the pitch, spindle speed and depth and just had it repeat it until it was enough (35 mm depth on intake, 25 mm on exhaust ports).
911 heads are good in this respect as they are straight at the start and even though very narrow at the start, they go bigger pretty quickly and by 35mm, they are almost 40 mm. Kind of wrong shape of taper.

I just used the probe to mark reference point (manifold contact surface) and gave it a go.

When dealing with more complex ports, its best to use 3D measuring machine (my employer has it) and alter the image like you want it to and then use Solidworks or Autocad to get the drawing into proper format.
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche