4 Cam extra performance

[Neil Bardsley]

I'm reading SH book on the 4 Cam and without wishing to start a mud throwing match there is some interesting technical details for a a beginner like me. Essentially, it seems like the differences

-> Cams for each cylinders
-> More (or longer sry can't remember) cooling fins around the heads
-> twin sparked because of higher compression and piston shapes
-> dry slump and external oil cooling
-> better material for the cylinder / pistons
-> Improve cooling from the fan and shroud

However,

-> The initial distributors which ran from the cam weren't great as they lost their timing quite quickly
-> The cam timing was complicated to set
-> The first development of the distributors which were driven from crank meant to change the belt you have to remove the distributors

I will lets someone that know what they are talking about come along and correct me but it seems like all of the above improvements save for the complicated bit the 4 cams could of been applied to the normal flat 4. Which is essentially that racing engines today are?

Seems that although 4 Cams are a very interesting engine it was essentially a too complex solution too the problem? Is being able to adjust timing for each cylinder an important part of the getting the most from these engines?

[Jacques Lefriant]

Hi Neil
In its day it was a great engine. DOHC makes different cam timing easier. Dry sump is a nobrainer. The 4-Cams had bad combustion chambers and really big ports. If we are talking air cooled boxers the 911 was SOHC the 916/908/917 were DOHC they have better combustion and ports mostly due to the valve angle. Now the 4 valve watercooled 996 engines are getting big Power to volume nos. so if you want the modern flat4 get a Subaru or wait till Porsche comes out with a 4 cylinder Boxer. Engines now have DFI so the bigest improvement that has 4-Cam legacy would be to use roller cranks and go to full roller like the 771 engines.
j

[James Davies]

The 4-cam was all about higher RPMs to get more power, a recurring theme in Porsche engine development. The type 528 (1500 Super) in 1953 topped out at 70 bhp at 5000 rpm. That same year, the type 547 (4-cam 1500) was good for 110 bhp at 7000 rpm. I think the main improvements were in larger bore and shorter stroke (85x66 vs 80x74), which reduced piston travel and increased valve area. Bigger valves meant better breathing, and the valve angles in a more hemispherical combustion chamber allowed for higher compression ratio. Everything else was just secondary in getting those primary design considerations to work.

What was the material used for early 547 pistons and cylinders? Was it different from the Mahle pistons of the period used in the push rod motors, aluminum alloy with hard chrome lined cylinder bores?