water pump pulley size

My Ford Capri 2.0 motor has a stock water pump pulley a little over 4" in dia. I have a 6" dia pulley from a Pinto 2.3 which I'm adapting to fit. I will also be increasing the alternator pulley from approx. 3" to over 5" dia. This change will reduce the speed of my alternator and water pump. The alternator probably won't charge until 2500+rpm but does anybody think I'm going too far with the water pump, reducing the speed by almost 1/3rd? Car has never overheated with the stock pulley.


Joe Craven
ITB Capri (primary car in '04)
ITB VW (rain and backup car)
ITA Capri (2005)

As someone pointed out in the tire size discussion, test it and find out for sure! Just take the pieces with you to the track so you can swap back to the stock pieces if you have a problem. I'd make sure the rest of the cooling system is in good shape just so you're getting a "good" test.

A 30% decrease in WP rotation led to overheating on my VW Scirocco.

As you probably know, the Capri 2.0 had a smaller crank pulley than did the Pinto version. It is the only reason that the larger water pump pulley can be used/will fit! Consider your self lucky!

Make sure that you are using a blanking sleeve with the proper size hole in it for the thermostat replacement, or use a thermostat (my preference), and give it a try. Forget the alternator...you don't need many amps for racing anyway, unless you are indurance racing at night.

One of my favorite modifications is to add a blank on the back side of the impeller to block off the holes in the back. It forces the water to be spun off radially from the impeller blades, instead of "leaking" thru the holes. A piece of aluminum and three pop rivits is all I ever used. Never had any evidence of cavitation, and I intentionally used a smaller than stock radiator (VW).

Good luck.

Bill