Engine Fan Drive Ratio

[KTL]

Thanks for the clarification. My 79 fan and housing are powdercoated by previous users, so I can't tell directly.

I'm upsizing to the 245mm fan to get more air from the larger dia. fan. Just trying to make sure I mix and match the right pieces, given there have been so many different fans and housings over the years. It basically seems like the 245mm housing changed in the rear on account of increasing alternator sizes over the years. Front of the housing shouldn't change since the fan pulley & crank pulley alignment needs to stay the same to maintain proper belt alignment.

[patkeefe]

Hi all,
I am dragging this up from the archives, as I need a bit of advise and clarification.
I'm building a street engine, 2.7, with EFI. I need to machine a pulley with the magnets in it to drive the SDS EFI system. I have a 245 mm fan shroud, 11 blade matching fan and new 70/75A alternator. Fan, housing and alternator have all been prior assembled and test fit for OK operation.

I have three crank pulleys to choose from: 115 mm, 125 mm, or a 135 mm OD. The 135 mm OD pulley is a cast pulley, with an integral smaller pulley cast in; that pulley is of 110 mm diameter. I would like to drive the fan with the 135 mm pulley, and drive the AC compressor with the 110 mm pulley. Compressor is if the Sanden variety (actually a Seiko unit). I will have to measure the compressor pulley diameter tomorrow. I am not concerned about possibly overdriving the cooling fan...street engine.

Question is: does anyone know what the drive ratio for the AC compressor should be? I can't seem to find this bit of information anywhere. Using the single integrated 135 mm pulley will make fabrication much easier for me, but if it becomes an out-of-range issue on the AC, I will go a different roue in fabrication (or, I will reuse the pulley currently on the 3.0 SC turbo engine).

TIA!
Pat