[ZeGermanHam]

Originally Posted by "QUICK-SILVER"

Three groove pulley doesn't mean it's the right size. Need to measure it and see for sure.

Clay

I just found that out for myself a few days ago. I ordered a billet pulley set for late 1969-70 with PS & A/C. I have a complete set of OEM pulleys to compare with, and as you know, the factory stacked a smaller diameter single-groove A/C crank pulley behind the 2-groove WP/Alt crank pulley.

When I measured my new billet 3-groove crank pulley, I noticed that it was significantly smaller than my OEM 2-groove WP/Alt crank pulley. I soon figured out that rather than machine the billet pulley so it has a smaller diameter section for the A/C belt like factory, they just sized the entire thing down to match the smaller diameter of the A/C crank pulley. This means that it will spin the water pump slower than the OEM crank pulley would. I was kinda bummed about that. They should size them up to match the OEM WP/Alt crank pulley size, not size them down to match the A/C crank pulley size.

[68WarDog]

Originally Posted by ZeGermanHam

I

The crank pulley looks small thats offered in the aftermarket (6"). Why would anyone want to underdrive the waterpump and alternator?

[ZeGermanHam]

Originally Posted by 68WarDog

The crank pulley looks small thats offered in the aftermarket (6"). Why would anyone want to underdrive the waterpump and alternator?

The billet crank pulley in my kit is 7-5/16", which is the same diameter as the OEM single-groove A/C crank pulley that would've been stacked behind an 8" 2-groove WP/Alt crank pulley. Wish they had just sized the thing up to 8" rather than size down to 7-5/16". Or better yet, machine the thing so it functions identically to the OEM setup and has two different diameters.

[64speed]

I have a cold case in the car right now. What is the absolute best radiator I can get?

[Singleton]

Originally Posted by 68WarDog

Why would anyone want to underdrive the waterpump and alternator?

Typically, Pontiac had their non-A/C engines underdriven by 8 to 15%.(water pump driven at 85-92% of crank speed).

The CVF pullies I have on my non-A/C GTO are both 6.2", (crank and WP), for a 1:1 ratio, (or 100%). The High-flow that CVF offers is the same 6.2 wp pulley with a 8" crank, for a 129% overdrive. I'm going to try a 8" wp pulley to underdrive it to 77.5% of crank speed. My engine idles at 1000, (manual trans), so the water pump will still be turning at 775 rpm. I run a flex fan with no cooling issues, but I don't like the fact that the fan is turning 6000 rpm at my shift points. By underdriving it 77.5%, at my 6000 rpm shift point, the fan will now be turning only 4650 rpm. Less stress on the fan blades and less drag.

[68WarDog]

[QUOTE=Singleton;6348546]Typically, Pontiac had their non-A/C engines underdriven by 8 to 15%.(water pump driven at 85-92% of crank speed).

Agreed, however Pontiac engineers weren't dealing with todays higher hp applications and performance standards. Also today's fuels don't provide the cooling and lubrication affect of the 60s and 70s.