LWP->SWP swap - Standard or underdrive pulley?

[dhardison]

I'm switching from a long water pump to a short water pump, relocating my alternator with a March kit and will also be replacing my stock pulleys with March billet units. My question is do I go with the stock crank pulley (7") or the underdrive pulley (5.5")?



My main reason for all these changes is to try and fit a Mark VIII fan to improve cooling. My concern with going with the underdrive pulley is it may not turn the WP fast enough at idle to keep things cool.

Comments/opinions?

Thanks!

[Lowend]

I never use underdrive pulleys. The power gain is minimal at best (maybe 2 HP) and the loss of rotation can really mess with alternators ability to charg.

[dhardison]

Thanks for the reply. The only reason I considered the underdriven pulleys are because the regular pulley kits are on backorder. I'll just wait.