3.2 cam swapping ? Should I?

JDaniel · JDaniel's Garage

Since I am a 911 owner, I can never be satisfied with what I've got. Now that the motor is out for a top end/clutch I've been looking around at different options for easily increasing the "oomph".

This time, before having my 3.2 put back together again, I thought I'd explore the idea of a different cam grind.
It's a stock 3.2 w/ a single in-dual out GHL, bypass pipe, and no other mods. Mostly street driven, but I do have some DE's planned for the future.

Is swapping cams a simple "switch" or do I need to worry about re-mapping the chip or any other additional mods?

What pros and cons are there with a change in cam grind? What options are there? Any advice or suggestions? I don't want to mess with changing the compression ratio.

Bill Verburg · Bill Verburg's Garage

The limiting factor for cams with longer duration than stock is the sensitivity of the air sensor to intake tract pulsations caused by the longer duration of the valve events at lower rpms. The most you can do is something like the 964 grinds that CIS users have installed. If a hot wire mass air sensor is also installed then you will have a little more leeway, but still not as much as with carbs or MFI. In addition the longer duration and lift cams really respond to equal length headers rather than the missmatched kludge that Porsche uses for an oem exhaust.

If it were my engine and 98mm pistons/cylinders were not in the cards then I would first put SSI's with a good free flow muffler then have the intakes manifolds flow matched then the 964 grind cams (don't try to use real 964 cams), then if I had an extra ~$2k an FVD mass air sensor.

Keep in mind that any cam with longer duration than stock (the 964 is only +11 on the intake and +10 on the exhaust relative to the Carrera cams, with a tad more lift) will lose a little at the bottom of the rev range for the gains at the top. All of the other mods(displacement, headers, flowed manifolds will help across the board)

It goes without saying that any engine mod should be accompanied by a remap of the DME chip.