HP generated from S90 and SC engines

[Rod R Youssefi]

Is the increased HP generated from the S90 or SC engines due to the carbs that are paired with these engines or from the intrinsic components of the motor itself compared to standard engine types?

[Steve Hatfield]

Head design, valve size, cam, piston and CR all contribute to the increase over less powerful but contemporary designs.

[Rod R Youssefi]

thanks steve

[Martin Benade]

Those two engines should be very similar in power but apparently the S-90 cylinder head is an under-performer. Compression ratio, port breathing and carb size were the improvements over the lesser engines, although the C and SC shared port and valve sizes.

[Ron LaDow]

Is the increased HP generated from the S90 or SC engines due to the carbs that are paired with these engines or from the intrinsic components of the motor itself compared to standard engine types?

The factory had what amounted to unlimited dyno time (Oh, but for the opportunity!)
Any engine, under proper development, delivers the power claimed as a result of carefully matching every part involved in the burning of the mixture in the chamber. Cam timing will determine when the mixture arrives and when the burnt remains exhausts. The carbs and intake are selected to match that, the C/R is a determinant also. All of those factors will tell the folks running the tests what ignition timing is required.
Pretty sure that quench area (and the possible CR increase) was not considered of value at the time. A look at the chambers of those building engines with more power now tell me they are working hard to find what the factory made no use of.
The lower end is assumed to be strong enough to handle the loads, once we got some decent rods.

[C J Murray]

Supposedly Hans Mezger was responsible for the "C/SC" engine improvements when he was a relatively new graduate of engineering school. He was credited with many successful engine designs including the Tag F1 championship winner over a 35 year stay with Porsche.

He determined that the 616 engine needed more exhaust flow and increased the exhaust valve size. I am not sure if he made any changes to the exhaust port. He also reduced the size of the intake valve which is often explained as he had to make room for the bigger exhaust, but I doubt that. You can, and we do, fit significantly larger intake valves for big displacement and racing engines. Surely he could have kept the S90 intake valves. More likely is that he was looking to improve torque at a lower rpm range which is in part determined by the velocity of the mixture as it passes the intake valve. Theoretically peak torque occurs when the mixture reaches mach at the valve so reducing the size of that restriction point forces the peak torque rpm lower. Mezger also made multiple detail changes to the intake ports for better flow.

Then Mezger looked to improve the burning of the mixture in the combustion chamber and decided to change the squish surfaces from 22* to 30* angle. Sometimes a change like that is done to adjust CR vs piston shape but I would guess he was looking for faster burn to increase power over a wide rpm range.

We know he experimented with different camshafts because he came up with a different cam for the C engine. That engine was a distinct improvement over the Normal or Super, both of which the C engine replaced. He must have tried some different cams for the SC but he kept the S90 cam that Porsche had borrowed from the A Super engine. The existing cam must have been very satisfactory to have not been changed by Mezger and to have been used throughout the 912 production.

All that said, the S90 is still a good engine but the SC is a little better. Maybe the C is actually the best?

[Steve Hatfield]

Thanks for the history lesson CJ. Timely and valued. And thanks to Rod for his initial question.

[C J Murray]

Thanks for the history lesson CJ. Timely and valued. And thanks to Rod for his initial question.

My pleasure! Will you be in Helen? I hope to see you there.

[Steve Hatfield]

CJ, wouldn’t miss it!

[John Clarke]

CJ , Steve
Interesting topic.
Don't want to degenerate Rod's topic , but who and where is Helen?
Cheers Jay

[Steve Hatfield]

Helen, GA
Southern Drive in Sep ‘19 every other year. A great 356 event in the Appellations. See in the events section of this forum.

[Steve Hatfield]

appalachians that is...

[Ron LaDow]

Supposedly Hans Mezger was responsible for the "C/SC" engine improvements when he was a relatively new graduate of engineering school. He was credited with many successful engine designs including the Tag F1 championship winner over a 35 year stay with Porsche.
[...]
He determined that the 616 engine needed more exhaust flow and increased the exhaust valve size....

Cliff, did I miss that in "Excellence..." or did you find it in another source?

[Doug McDonnell]

I am a bit surprised that Vic hasn't chimed in. He refers to the S90 as an S85 sometimes. I have seen the C described as Low end torque of a Normal with upper end power of a Super. Maybe by you CJ? Of course my opinion may be influenced by having a C.

[Vic Skirmants]

I don't need to chime in after Cliff's excellent treatise.