S cams

[speedo]

I have been looking through Bruce's book and Waynes...and wonder at the differences between all the S cams. Seems like there are two basic cam grinds. The original S profile looks the same from 67-73, and then 75-77 it changed. Then the 964 grind seems to be used in later S type later displacement motors. ...3.0 and on up. I realize these cams all differ in overlap...and when the overlap starts and ends.

Has anyone used the 2.7 S cam in early S motors?

Has anybody used the 964 cam in early S motors?

Is it easier to regrind a later S cam to an early profile...or an early T cam to an S profile?

If these are really stupid questions...don't do the "Lord of the Flies ...death to piggy" thing...just bring me up to speed.

Thanks,

Speedo

[Early_S_Man]

There were two early 'S' left cams ... carbed and MFI. The MFI cams were used from 1969 thru early 1976 production. The last application was for the 1973 2.7 RS and 1974 - 76 ROW Carrera engine Type 911/83. Left bank CIS cams don't have the MFI drive hub for the toothed pulley. There is said to be an adapter available to allow mounting the MFI pulley on non-MFI cams, but it is probably NLA, now!

The 1974 - 77 CIS 911S cams for USA markets -- both Federal and Cali ... would be useless in an early 'S' engine, as they would not match the desired airflow and torque characteristics of either the carbs or MFI system calibration!

Either Web-Cam or Dougherty Racing cams can regrind cams.

[Walt Fricke]

Speedo

I think what got you confused is the trick Porsche tried in 1974 and 5. For the US market all you could get was a CIS 2.7 engine. This requires a milder cam, nothing like the earlier S (or even E) cams, whether for carbs or MFI.

Porsche also decided that it should offer an S model and a "normal" or non-S model. I guess they thought they'd sell more cars that way even though the non-S can't have saved them any money to build. The non-S came with a lower compression engine (done with the pistons), smaller ports in the heads, and an even milder cam. Maybe it also had the M calipers up front as well. How any of this saved them money I'll never know as it can't have cost more to make the higher performance parts, but perhaps it is smart marketing. Maybe they thought customers were used to seeing the T, E, and S and wanted to keep up the tradition of choice.

So that is what differentiates the S and non-S CIS cams.

For the '76 and '77 2.7s they stopped all this foolishness (and by then they had the turbo as the flagship in the US) and also stopped calling the 2.7 an S.

As was pointed out, the CIS S cams are nothing like the cams used in the early S cars (which, therefore, we all call S cams). And after the 2.7s Porsche pretty much quit using "S" for its cars aside from the C4S and C2S.

Walt Fricke

[ficke]

You can grind a 906 cam to an "S" and a "S" to a "Solex" and a "Solex" to a "E" an "E" to a "T" but to got the other way usually requires welding build up to get enough material to grind the lift and duration necessary. The CIS fuel injection used on the mid year "s" does not deal well with overlap air pulses of most high RPM cams.