does it matter what size pulleys you use to spin these items IF you maintain the desirable ratios needed to operate at the required output ? in other words, if a stock set of pulleys consisted of a 6 1/2" crank, 7" water pump, and 2 1/2" alternator pulley, could you substitute a set that was a smaller diameter, but contained the correct ratio that would run the items as designed ? my gut says yes, but what say you ? [ i think of things too much.....]

with the Mopar alt low RPM charging issues spinning it fast is always a good thing and there are 2 sizes of alt pulleys and the largest crank pulley is I believe a 7&1/4 and I have ran into a pump pulley that was big enough that the 7&1/4 crank pulley would not work. it is possible to spin the pump too fast & get into cavitation at higher RPM's but I wouldn't sweat that & the cav plate (easy to add) pretty much elims that & gives you a far more efficient pump. Short version: the big prob with pulleys is matching a set with the right depths/offset so the belts line up. I'd use the smaller alt pulley and the 7&1/4 crank pulley and a pump pulley roughly close to its dia (not a dealbreaker) whatever you have of the right depths for belt alignment and using as short of belts as possible is always a good idea

Yes, the ratios are what's important, not the diameters.

that's what i was thinking guys. i'm toying with some ribbed pulleys and ratios using a standard rotation water pump. thanks guys !

Don't forget that for a given RPM a larger pulley has a higher speed around the circumference, which could cause the belt to jump.

More info than you probably want in the link

https://books.google.com/books?id=1LS2Bg...ing&f=false

yep. was using my "hand book" as a reference to see how much higher the belt speed would be, and if an idler of some sort would be necessary as a precaution. this was also taking the manufacturer red line of the donor engine into consideration, plus the average rpm cruising speed [just a guesstimate] of the vehicle. the pulleys in question are slightly smaller than the original mopar v belt setup.