Cam timing on stock 3.2 with PMOs

[sandiego]

Should I change the stock timing when putting PMOs on an otherwise stock 3.2 which is used exclusively on the track? One mechanic said "advance to 2mm", and another said "retard to 0.9". Thanks.

[Flieger]

You should change the cams to something more aggressive or you will not get much more power for the trouble of the carburetor conversion. 911E or Solex or S cams would really wake up the top end.

I am not sure how to adjust the timing on your stock cams but I would not expect too much difference myself.

[Eagledriver]

The standard spec for your engine is around 1.3mm. If you are going to rev the motor above the stock redline then I'd retard the timing to around 1mm. If you want more low end torque then advance to about 1.7mm. If you have short gears then you can keep the revs up and use the retarded setting. This will make a nice track motor and will pull to 7200 (assuming you have stronger rod bolts and stiffer valve springs).

-Andy

[911-32]

Originally Posted by Flieger

You should change the cams to something more aggressive or you will not get much more power for the trouble of the carburetor conversion. 911E or Solex or S cams would really wake up the top end.

I am not sure how to adjust the timing on your stock cams but I would not expect too much difference myself.

None of those cams will work with the std 3.2 "smog" pistons that do not have valve cut-outs and hence cannot work with a higher lift cam - 993 Supercup or 20/21 or Super C2 grinds are generally about the limit on a std 3.2.

In the UK people have used webers on std euro 3.2s for rally engines with approx30-35hp gains and better throttle response when combined with SSI/early exhausts. The last engine my mechanic swapped to Webers gained 30hp without any change in cam timing. An ITB/carb intake will certainly make more hp than a common plenum single throttle body intake even on std cams though more gains are certainly possible with other cams.

RB

[sandiego]

Thanks for the replies.

This was a salvage engine from a fuel fire that cooked all the FI components. I threw on the PMOs because that's all I had. Ran it at one TT and it ran great. Excellent response out of the corners. Its now out to fix some leaks so I thought I'd consider changing the timing.

The idea of throwing in some S cams was intreging, but I guess that wont work without different pistons. Maybe this winter.

Again thanks.

[KTL]

Changing the cam timing from spec for performance can be dangerous when you go outside the acceptable range of spec. If you increase the lift at TDC overlap spec, you may be approaching dangerous piston-to-valve ("P-V") clearance. It's best to make sure you check your P-V not only at the TDC overlap point on the crank, but also well before and after.

I know we're talking stock pistons and cams here. Still, it's worth checking. As as aside, when I put in a reground stock cam (DC20 from camgrinder) to be used with my stock 3.2 USA spec pistons, I found that I did not have adequate P-V when setting the cam to the recommended 2.2-2.4mm spec. I had to back it down to 1.85mm. And note that the minimum P-V clearance I found was not at TDC overlap, but quite a bit beyond/after TDC overlap.