Factory Reject Rate for Casting 4 Cam Heads

Discussion of 4-Cam Type 547 engines (and all the Fuhrmann racing variants) and cars that powered them.
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Bill Sargent
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Factory Reject Rate for Casting 4 Cam Heads

#1 Post by Bill Sargent » Thu Jul 07, 2022 4:03 pm

I was recently corresponding with Andre Mossner who owns Retro Design 3D in Germany. They manufacture, among other things, 4 cam heads. We were corresponding about the difficulty to cast the heads and problems with porosity etc. Andre provided some information on the in period Porsche factory reject rate for 4 cam heads. A partial quote of Andre’s email is shown below.

“Casting the heads is not to be underestimated, it is extremely difficult. When I started the project, I was with the original fabricators of the heads near Stuttgart. They even still had the original drawings. During the conversation I was told that they had to scrap over half of the heads after machining because of porosity and leaks”.

Given the hi reject rate for heads you can see why a carrera cost nearly double what a pushrod car cost.
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Jacques Lefriant
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Re: Factory Reject Rate for Casting 4 Cam Heads

#2 Post by Jacques Lefriant » Fri Jul 08, 2022 12:12 pm

i was told that back in the day the mold took 43 pieces to assemble. many raw castings did not make it to the machining step. Now a big portion of the molds are done by 3D printers which can make more intricate cores. https://nam12.safelinks.protection.outl ... reserved=0
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John Brooks
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Re: Factory Reject Rate for Casting 4 Cam Heads

#3 Post by John Brooks » Fri Jul 08, 2022 11:47 pm

Anyone know Elon Musk? His casting machine could probably do them a few dozen at a time, and with no porosity. The tooling would be expensive but it would be right.
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Harlan Halsey
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Re: Factory Reject Rate for Casting 4 Cam Heads

#4 Post by Harlan Halsey » Sun Jul 10, 2022 3:56 am

The Carrera cylinder heads are a straightforward design, just what Furman thought he wanted I guess, but never optimized because they could be made at the time in post war Germany. They are difficult to make because they incorporate copper oil passage tubing and because of the high aspect ratio and close spacing of the fins. Furthermore, the gas passages are way too big. Essentially, they made a 9,000 RPM head and put it on a 6,000 RPM bottom end. Nevertheless, the Carrera is one of the most successful race engines of its time.

If there were a market to justify the cost, a modern optimization aimed at the original bottom end, would eliminate the copper tubing, simplify the manufacture, take another look at the finning, and optimize the gas flow for power at lower RPM. Apparently, this is what the Garretson/Kuzu three-piece redesign can do. They have not optimized the gas flow yet. If they are successful, we will have brand new cylinder heads which look just like the originals but are cheaper to make and make more useful power.

A more extreme optimization would look at the combustion chamber and probably conclude that a more 911 like chamber would produce more power but require different valve angles. But to what purpose?

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Re: Factory Reject Rate for Casting 4 Cam Heads

#5 Post by Jacques Lefriant » Mon Jul 11, 2022 12:16 pm

Hi Harlan
the current available heads from Capricorn and Andre Moessner using modern casting methods are pricy but they meet our needs. i am of the opinion that changing the combustion chamber to 911 specifications is the only way to go since there has been 35 years of development.
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Martin Benade
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Re: Factory Reject Rate for Casting 4 Cam Heads

#6 Post by Martin Benade » Mon Jul 11, 2022 1:39 pm

If the stock head design (ports) is suited to very high RPM what limits the bottom end from keeping up?
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Re: Factory Reject Rate for Casting 4 Cam Heads

#7 Post by Jacques Lefriant » Mon Jul 11, 2022 6:41 pm

3 main bearing crank and marginal rod bearings
 

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