ohioredrx7

iTrader: (13)

This weekend I added the air pump back onto my RX7. Previously the engine that I had purchased had come with the Greddy water pump/alternator underdrive pulleys installed with the air pump deleted and the corresponding shortened serpentine belt.

As many other people had noted the wrap angle around the water pump pulley is very small and can result in the belt slipping at high engine speeds.

After a lot of searching on the forums I could not find a thread that definitively defined the correct belt length for my setup which is:

Greddy underdrive water pump and alternator pulley
Stock main "crank" pulley
Stock air pump pulley

All of the threads were either never followed up or ended with "use a string." So I thought I would post what belt length was appropriate for my setup in case other people are looking for the same info in the future (myself included in case I forget.)

The belt length that I found to work was a 54" 5-rib serpentine belt. Though slightly longer than desired (I was hoping for something between 53.5-54" but these are not normally stocked in auto stores) it is short enough to compensate for belt stretch down the line.

I purchased the following belt from Autozone but have included the Goodyear equivalent below.

Duralast part number (Autozone)
540K5

Goodyear part number
4050539
5PK1370

I know many people have said it before but after seeing it myself (this is my first RX7 that I've owned) the amount of belt contact on the water pump pulley lost by running just the Greddy pullies without the air pump or aftermarket air pump delete pulley is ridiculous and definitely not an acceptable solution from an engineering standpoint.