Originally Posted by c32AMG-DTM

Hey jturkel,

Let's assume you're at a load level where the S/C is engaged.

All things being equal (like your note of proper tuning of fuel/timing/etc), the "gear" ratio between the S/C pulley and crank pulley is what's important. So, the performance (rwhp/rwtq) of a 178mm crank w/ mid-sized S/C pulley would be identical to a 181mm crank with slightly larger S/C pulley that kept that ratio the same. The minor footnote to this is that as the crank pulley gets larger, you're overdriving the accessories, which increases parasitic losses (i.e. losing efficiency of getting power to the drive wheels). That said, as you decrease the size of the S/C pulley, you lessen the belt tension, and the surface area of belt contact on the S/C pulley - presumably increasing belt-slippage (i.e. losing efficiency here as well).

My guess (and it's only a guess at this point) is that the 178mm crank pulley, plus the mid-sized S/C pulley, will make roughly the same power as the 185mm crank pullied cars - again, assuming proper tuning and other variables have been addressed. The 178mm car *should* be more efficient as well, due to lower parasitic losses; how much? Dunno. Apples-to-apples, it's also worth mentioning that buying a 178mm pulley kit, AND a mid-sized S/C pulley, would be approximately double the investment of a 185mm pulley kit and leaving the S/C pulley stock. To some, that may make a difference... YMMV.