Broken 964 distributor belt cost 37 hp

[175K911]

Stupid $8 distributor belt that broke on the dyno cost 37 whp. That’s the actual power loss while on the dyno. And that’s hp at the wheels! I guess after 25 years it was due for replacement.

Our host overnighted the new belt, now just have to put the dizzy back together and into the car.

[75 911s]

The power of dual spark.

[uwanna]

On my 964 3.6 the only symptom of my broken belt was intense pre-ignition knock on hard accelleration from low RPMs. Certainly not good for the motor. Had me perplexed for a bit till I found it!

[Jeff Alton]

Good it was caught Ed, can lead to some new pistons and rings.....

Yes, important from a power point of view as twin plug ignition timing advance is reduced because of the far better ability to ignite the charge. This also add greatly to rod bearing life especially in high rev/load use. The more power you can make at the least advance the better for rod bearings.

Cheers

[175K911]

Originally Posted by uwanna

On my 964 3.6 the only symptom of my broken belt was intense pre-ignition knock on hard accelleration from low RPMs. Certainly not good for the motor. Had me perplexed for a bit till I found it!

Yup, in my case though the knock sensors looked like they were working overtime constantly pulling back spark, the dyno plot for that pull were all over the place, not a smooth curve. And I was running 100 octane Sunoco Cam2.

[Mahler9th]

I suggest inspecting all distributor components carefully, including bearings. I had one fail and the eventual result was a broken crankshaft.

[175K911]

Mike, bearings looked and felt ok so I put it back together just to get back on the dyno. I’ll order up new bearings and do a full rebuild in a month or so, just have a time constraint right now. But good thought, thanks.