Now you need to look at wire diameters, materials, natural frequencies of the inner and outer springs, acceleration rates of the cam profile, the changes in acceleration rate(jerk),
valve seating velocities, moment of inertia on the rocker arms, the interference fit between the inner and outer valve springs, does the retainer fit the springs tight enough to dampen vibrations, and a few others im too tired to remember.
The 906 is what I would call a slow acting camshaft, low lift with lower velocities.
In comparison our 306/288 cam at 8000 RPM would need a lot more valve spring pressure to survive.
Our race spring sets up at 39.5 mm with 100 lbs and has 410/ in rate. It was designed by us for the 306/288 and larger cam grinds and made with a very high quality wire.
To calculate open pressure take the spring rate and multipy it by the valve lift and add the closed pressure.
410lbs x .500 = 205= 100 = 305 open pressure.
I believe the higher open pressures and increased friction is a fair trade off for a stable valve train. If the spring is not up to the job and the rocker arm leaves the cam lobe (lofting) the rockers wear, the valve springs get beat up, the valve stem tips and get hammered etc etc.

If Dema was your teacher, I will second, third, any info you provide. Was he?

Yes!
He was when I was at De-Anza college,
and for the last 14 years at Elgin Cams.

Then with all the authority I have ( please don't challange this..OR ELSE!!) I pronounce you a true cam expert. If anyone wants to look into my pronouncement, you will find one of the most respected and knowledgeable people in the world, of cams, is Dema Elgin, of Elgin cams. Any student, or accomplis, of his, especially one with such longevity is worth listening to, very closely.

And hes Irish to boot! Can't be all bad.

Welcome aboard.

Okay Camgrinder - I'd like something a little more radical than a 330 cam, but something that'll still work with CIS induction and pistons, and also work with a stock valvetrain. 20/21 is what Webcam offers. Do you guys offer a similar cam to the Webcam 20/21?

Thanks.

The next step up from our 330 or Sport SC is the 964. I believe the 20/21 lies between our Super/C2 grind and our Sport 964.
Both I wouldnt use in your case.

Thanks for the endorsement Snowman.

Why? Too hard on the stock valvetrain?

Both of those grinds should have an upgraded valve spring. The Super C2 works good if the compression is raised to 9.8-1
The other variable is the CIS.
The 964 grind is stable with stock valve springs up to the usual rpm limit of 6500 with CIS so it works nicely. Regrinding the SC cams to 964 specs remove very little from the base circle (.030")
by far the most popular Porsche grind we do in the last 2 years.

Camgrinder(John) what have you got for the 3.6 and 3.8 in general?

and more specifically what have you got for a 3.8RS mostly street use?

Bill,
there are a few options available.
Super C2 248/236 duration @ 1mm
.475"/.455" valve lift
Sport 964 254/236 duration @ 1mm
.490"/.455" valve lift
284/274 254/244 duration @ 1mm
.490"/.460" valve lift
All of these grinds work well in the 3.6 litre and up engines and the choice depends on your mods and driving style.
The sport 964 is a little more than the 3.8 super cup cam. and the 284/274 is another step up.

John - can the sport 964 cam work in an SC engine? If so, how would it behave?

Thanks.

The Sport 964 cam needs over 9.8-1 compression and might have a choppy idle in the SC. I have not sold it to anyone that has put it in an SC.

Thanks, I'll do that:)