Engine Pulleys

The air conditioning system I selected (Vintage Air) required me to locate and purchase two sheave water pump and crankshaft pulleys. I spent way too much time choosing what pulleys to purchase and install, as overthinking is something I’m very good at.

At first I planned to simply order the pulleys from CVF Racing as they sell matched sets with one, two, or three sheaves. I was all ready to pull the trigger on their two sheave pullies until I thought about what ratio I really needed to keep up the water pump and alternator speeds, as well as what diameter crankshaft pulley the Vintage Air system was designed for. The alternator and water pump would be no problem if I just bought the water pump, crankshaft, and alternator pulleys as a set from CVF Racing. The CVF crankshaft pulley is quite a bit smaller than the factory pulley. This meant that the A/C compressor would turn more slowly. This may or may not be an issue for the compressor that Vintage Air includes with their kit.

I decided to dig a little bit deeper to see what the car would have come with if it had factory air and to see if Vintage Air had any recommendations. Looking over the online instruction manual for the Vintage Air compressor bracket installation I found this note:

This bracket was designed using a 2-groove water pump pulley #C8AE-8509-B and a 3-groove crankshaft pulley D3TE-6312-AB.

Now i had some part numbers to research. I found this great site with information on many Ford crankshaft and water pump pulleys. Unfortunately that site didn’t have the pulley diameters for those particular part numbers. After further research I was able to find that my car, if ordered with factory air, would have used a C6AE-8509-A water pump pulley (2 sheave 5.86″ diameter) and C4AZ-6A312-B (3 sheave 6.20″ diameter) for the crankshaft pulley.

The Ford shop manual had some information regarding pulley ratios for Mustangs with and without factory air. Without factory air the ratio was 1.06:1. With factory air the ratio was listed as 1.34:1. This didn’t match with the diameters I stated above, but I decided to shoot for something between the two ratios. The CVF high flow pulleys had a ratio of 1:1 so the water pump speed should be acceptable with those pulleys. However the crankshaft pulley had a diameter of 5.4″, so the ratio for turning the air conditioner compressor would be slower than the factory pulleys.

I decided to attempt to match the factory pulleys as best as I could, although the diameters I ended up with were just a bit different. This would result in turning the water pump at a ratio of 1.15:1. I found that the water pump pulley I mentioned above is reproduced so I could just purchase it from one of the Mustang parts suppliers.

The crankshaft pulley is not reproduced. Since I have an aftermarket harmonic balancer (Professional Products 80009) on my car with bolt patterns and spacing that will work with the old or newer (post 1968) pulleys I had more choices. For the crankshaft pulley, I chose to use the C8AE-6312-E pulley, which came on many cars starting in 1968. It has two sheaves with a diameter of 6.75″. This gave me a ratio of 1.15:1 and I could retain the stock alternator pulley. I would probably lose a few horsepower turning the water pump a bit faster but I decided that was better than overheating or not charging at lower speeds since I do some driving in traffic and in parades. That pulley works with my balancer if I use the spacer that was included with the balancer.

I located a pulley on eBay and made an offer which was accepted. Here’s a picture of the pulley I purchased.

I did some preliminary testing for the inner pulley alignment using a laser pointer (cat toy). I can’t test the outer pulleys until the kit actually arrives and I install the compressor. To check the alignment, I placed the laser pointer in each of the pulley grooves, one at a time. For each pulley I spun it around until the pointer light was shining towards each of the other pulleys. The light from the pointer landed directly at the center of each of the other pulleys. That means the pulleys are aligned.

I tested and am able to use the stock fan belt to drive the alternator and water pump. This was unexpected as I changed the pulley diameters. When I receive and install the new compressor and bracket I will be able to test alignment of the outer pulleys and measure for belt length.

Since the pulleys are not included in the A/C kit I ordered I felt that there was some degree of risk in finding pulleys that would work with both my engine and the A/C kit. I feel that this risk has now been mitigated somewhat since I know I have good pulleys and pulley alignment. Time to move on to anything else I can complete while I wait for the A/C kit to arrive.