Wide Lobe Cams

[Mike Horton]

Craig Richter, in his "How To Make An Old Porsche Fly" book, from '83, stated the rocker arm ratios actually measured at 1.24, and 1.07...
Craig also did an in depth analysis, and said the big can mufflers, came in tune sooner, and stayed in tune longer, and gave his reasons, based on wave theory, which I studied in physics.

One reason I've always agreed with C.J. on the stock S, S90, SC, 912 cams for daily, and cross country cruising, is the great torque match with the as delivered gearing, tire OD, and typical road speeds, a different reality for me at 72, than when I built my first autocross engine at 20... and I'll admit, I have more actual road miles on TX, & NM highways, through the years, in my old Normals, than even my 912, in which I commuted for several years. I love this conversation, as we get actual user inputs, from those who've been there,

[C J Murray]

I would like more complete data but here is a start...
http://www.pelicanparts.com/356/technic ... _stats.htm

Points of interest...

peak torque/rpm: N-11.2/2800, S-11.9/3700, C-12.5/3600, SC-12.6/4200

Peak torque rpm is where an engine feels strongest and where it operates most efficiently so without seeing the actual torque output at all rpm I can safely say that a C makes considerably more torque at 3600rpm than does an SC. To exceed the C torque with an SC you have to increase engine speed nearly 600rpm. If we did have all the data at all rpm the huge advantage to the C vs SC would be below 3600rpm, guaranteed.

[Jacques Lefriant]

CJ
Torque may feel good but the operative term in Physics is work or energy: horsepower. basically the work done is given by multiplying the torque by the rpm.
j

[C J Murray]

Ask the owner of the car where he/she is in the habit of shifting the car to the next highest gear. This answers the question of which cam and carbs are best for them. If the driver is habitually shifting at 6000 rpm then the SC is more powerful and better for them. If they rarely go beyond 5000 rpm then the C is more powerful. More torque for any given rpm means more HP at that rpm. What wins races is the average power within the usable or required rpm range. The important factors are how many gears do you have and how the course you take determines what rpm range is used.

For a street car the conditions are diverse and challenging so the engine needs to be flexible. We also have only 4 gears so the rpm drop to the next gear is substantial. In casual street driving torque is your friend. Some people like to drive their car more aggressively and would not be happy with a 5000 rpm or lower shift point so the SC cam is a better choice if they don't mind the less responsive throttle say between 2000-3600 rpm.

For many drivers they just don't like the more hyper mechanical character of turning higher rpm, they never do it, and they would be better served with a C.

The aftermarket high performance cams are for people who continuously exceed 6000 rpm.

There is no such thing as a magic camshaft. There is no such thing as a camshaft that improves the entire rpm range. Whenever you increase power at some rpm you loose power at some other rpm. As you push the peak power rpm higher you reduce the width of usable rpm. By the time you get to a true racing camshaft the usable rpm range is extremely narrow to the point that only an extreme close ratio transmission makes the car drivable. Thank God tracks don't have traffic lights.

Pick the cam for how you drive or for the rest of your engine specs. A S90/SC/912 with Solexes needs the cam to match or it won't work well. Zenith engines can use a C or SC cam. Porsche concluded that the C cam was better. Stay away from hot rod cams unless you have a plan focussed on more aggressive driving.

[Jacques Lefriant]

Hi Cj
That is why they call Normals Damen. most Porsche drivers usually prefer "spirited" driving the reason 912s were not big in Europe was because they were blown off the Autobohn. I gave up on my 1600N T5 coupe when i could not keep up with a VW fastback on the freeway. I don't consider the slightly larger replacement cam an impediment to anyone's driving style. it has been the go to cam from the 60s. OK if all you do is go to the local Starbucks use the Normal/C cam.
j

[Ashley James]

Excellent post CJ, I wish more owners of a whole raft of classic cars would grasp that and accept that old cars are best accepted and enjoyed for what they are.

I’ve got an SC engine and the opportunity to swap it for the C that’s in the car but I’d already decided to stick with the C because it’s just as you describe.

[C J Murray]

What do you have against Starbucks?

[Ashley James]

My little 356C is quite able to keep pace on the Brit motorways at eighty plus, but I have a ceiling of seventy five because the poor little thing is revving it’s head off. That’s just under 4000, so I’d need to be doing about a hundred before the SC cam comes into its own.

Starbucks and my license would both be a blur in my rear view mirror.

[Martin Benade]

I think the engine likes 4000 rpm better than you or me like the noise.

[C J Murray]

Well said Ashley. My wife and I do a lot of long distance driving and the cars will go fast if you want but the intensity of the mechanical noise and air turbulence takes a toll above 70 or so. We run with normal traffic fine but much faster is not good for long periods.

[John Willhoit]

Here is the list of camshaft specs. They are all correct as tested on a cam doctor or given to me by the grinder.

[C J Murray]

Thanks for posting that John.

I thought that you had some cams with different intake vs exhaust lobes, and some with wider lobe centers?

[Vic Skirmants]

MANY years ago I rebuilt a local C engine. Only change from stock was 86mm pistons and a Bursch exhaust. That car would out-run any SC around. You didn't have to go to 6000rpm. The torque would take care of things until top end in 4th gear.

[Martin Benade]

Do you suppose it might have been even better with a stock muffler?

[Mike Horton]

MANY years ago I rebuilt a local C engine. Only change from stock was 86mm pistons and a Bursch exhaust. That car would out-run any SC around. You didn't have to go to 6000rpm. The torque would take care of things until top end in 4th gear.

...the very basic concept of adapting the high torque, and custom factory paired gearing, to optimize the Type IV engine, in the 914s, & 912 E, an underappreciated concept, which endears the N & C, to so many, ...

Damen, indeed, racers exempt...