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PostPosted: Tue Feb 28, 2017 11:55 pm 
356 Fan

Joined: Sat Nov 21, 2015 12:48 am
Posts: 12
So...
The 'C' cam is a great street 'feels good' w/torque and great drivability.

The 912 cam makes a bit more power but less torque, great drivability.
More duration (240) even less torque?
Why is the 912 grind better than the C for strictly street use? How many of us rev to 5 grand on a regular basis?
I seldom see the tach go north of 4 myself.


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PostPosted: Wed Mar 01, 2017 1:04 am 
356 Fan

Joined: Thu Apr 01, 2010 4:35 pm
Posts: 698
I went with the Schneider cam on the advice of my machinist who said it would lower the power ban, meaning I wouldn't have to wait until 5k plus for the horsepower to really kick in, which is what I have with my 912 using, I assume, a stock cam. Maybe I need to do some reading about this whole duration thing.

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PostPosted: Wed Mar 01, 2017 8:50 am 
356 Fan
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Joined: Fri Oct 23, 2009 7:24 pm
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Location: 30MI WEST OF PHILA
Putting together the right combination to get the desired result is complicated. The camshaft needs to be matched to the CR, port flow, carburetors, and exhaust so when any one of those is modified it may be necessary to modify the others. Car manufacturers spend enormous amounts of time and resources to develop engines that work seamlessly and we as individuals just don't have those resources. If Porsche decided today to further develop the 616 engine they could, after much effort, produce much better street performance as well as better manners. Unfortunately we are not as smart as Porsche so we need to proceed with caution when changing our engines.

In general, all other things remaining unchanged, more cam duration pushes the peak torque and HP up higher on the tach. At the same time the range of usable rpm gets ever more narrow as duration is increased until you get to a point that the available rpm range is unacceptable for practicality. For conservative drivers possibly wanting better fuel mileage and fewer repairs driving long distances or in urban use the C engine was the ultimate development by Porsche for the 616. For the customer that wanted more performance the SC was as far as Porsche wanted to go to avoid durability problems or customer complaints. The SC had a bit more duration, more lift, higher CR(to make up for the lost dynamic compression caused by more duration), and larger carburetors.

One fact about engine modification is that the further you go the more impressive the sensation of power becomes. This is because you are reducing power in the lower rpm and increasing it near redline and that results in a seat of the pants rush that can be very misleading. Most likely your car is getting slower as you drive it in normal street use. Think 911S vs 911T and check out those cam specs.

These are pretty solid rules of thumb but they are not cast in stone so your results may vary or your personality may benefit from a peaky engine. It's your choice.

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PostPosted: Wed Mar 01, 2017 8:51 am 
356 Fan

Joined: Wed Nov 23, 2011 10:52 am
Posts: 2616
Location: Cleveland, Ohio
He probably meant power band. If your 912 really doesn't do much until 5K rpm either its not stock or something is wrong with it. I am guessing that no aftermarket cam gives a lower power band than the stock one.

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PostPosted: Wed Mar 01, 2017 12:42 pm 
356 Fan
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Joined: Mon Dec 06, 2010 1:50 pm
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Location: National City Ca
Hi CJ
the point i am trying to make is there might be a better fit than the stock cams for a particular individual. Even thought my hero Metzger may have had some input the C cam is basically a revamped Normal cam. Here in California the cam grinders have had a great deal of experimentation with cams for both the VW and pushrod Porsche engines. in my opinion Porsche did not want to address optimizing the profiles like they had to do for the 911 even for the 2.0 they had the Solex grind, the basic grind for the new headers, the 911S, the 911T, 911E, 911SMFI, 906, and tuners like Shreck offered more grinds. Also 911s can advance or retard the cams easily. If you talk Carreras they have 5 stock lobes so you can do 25 cam different combinations before you time the events.
j

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PostPosted: Wed Mar 01, 2017 3:18 pm 
356 Fan
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Joined: Fri Oct 23, 2009 7:24 pm
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Location: 30MI WEST OF PHILA
Jacques Lefriant wrote:
the point i am trying to make is there might be a better fit than the stock cams for a particular individual.
True! I am just saying that most of our cars are driven in a way that an SC cam is plenty. I am trying a C cam with 8.75CR this Spring and if it pulls ok to 5000rpm I think it will be a great combination for the average 356 owner because it is sure to be great in traffic. Solex carbs would be too large for that cam and spoil the low rpm smoothness and power.

The common asertion that a hotter cam is good for everybody's car is wrong.

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PostPosted: Fri Mar 03, 2017 11:43 pm 
356 Fan

Joined: Sat Nov 21, 2015 12:48 am
Posts: 12
What is a safe compression ratio to run with pump gas?
I normally run 91 octane that is 'pure gas', no ethanol in my stock engine. No ill effects to rubber parts with this formula.
Is 93 required for a 9.0 to 1?


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