hb4

Working on my AC for my AT car, and have discovered that a PO has installed what I believe to be the crankshaft pulley from a manual (928 102 110 04). It appears to be about an inch smaller than the auto pulley (xxx xxx xxx 03) when comparing it with my buddy's AT car.

I am looking for the diameter of these pulleys to determine what the engine speed would need to be to reach the compressor speed of the auto pulley during idle. Does anyone have one or both on the shelf that they would measure for me?

Any idea why these would be different between AT and manual shift cars, and what effect they have on AC performance?

Tom. M

Sounds kind of odd that there would be a different pulley for manual vs. auto. I could see different sizes based on the rear ratio yours being 2.54 it spends more time at higher rpms....than Jeff's which is a 2.2. Probably have a smaller pulley to keep from over revving the compressor? just a swag.. I'll have to look at mine tomorrow and see if I can get a diameter on it..

hb4

Thanks, Tom.
PET shows the larger (03) pulley for MY -89, and the smaller (04) pulley for MY 90-. The compressors are different as well, so maybe the pulleys depend on the compressor. I have a Seico compressor so who knows what the heck it takes.

I have Pappy's receipt from an Anaheim shop listing PN xxx.xxx.xxx.04 and stating "R&R A/C drive pulley w/smaller pulley from manual style vehicle".

I think the change was made by the PPO to reduce parasitic HP loss.

We did a quick measurement and found that my pulley measures 1" vertically (axially) from the tip of the PS flange to the tip of the AC flange. Thomas' (MY 88) measures 1-1/2". Didn't try it with Jeff's. Interested to see which one is in your '89 manual.

dprantl

Are you sure it is a Seiko-Seiki compressor? No 928 came stock with such a compressor. Stock is either Behr/Bosch ('78-'79), Nippondenso 6E171A ('80-'89) or Nippondenso 10PA20C ('90-'95).

Dan
'91 928GT S/C 475hp/460lb.ft

hb4

It is a Seiko compressor, installed by a repair shop for the 2nd owner. Looks like the one on this thread.

Anyone know how they perform relative to the stock ones?

PorKen

Interesting. Different size pulley for M481/249.

(Learn something new every...once in a while.)

Tom. M

I just measured mine from the top of the PS belt channel (sitting on the belt) to the top of the A/C belt channel and it was just a hair under 1.5". As far as I know the belt assembly on the front of my car is original..

I wonder if your swapped in A/C compressor needs to be spun at a slower speed? Probably best to search the specs on that compressor and then grab a stock pulley if you can increase the RPMs without messing the compressor up.

hb4

Tom,
Thanks for checking; so manuals had a different pulley and, I believe, compressor.

I did a search for the compressor, and found a similar one with 7000 RPM max spec. Since both pulleys are about twice the size of the compressor pulley, I don't see how that would work with our 6000+ red line.

Since the compressor was installed five years before the pulley by a different shop and owner, I'd be surprised that anyone tried to match the pulley to the compressor; especially after it ran successfully (apparently) for those five years. I really think it was Pappy looking for a few tenths of HP.

Anyone have the diameter of either one of these pulleys handy?