No, a "yoohoo" belt is just a very short standard v-belt that connects the main pulley and the waterpump.
Because there is no idler/tensioning pulley involved it must be a close fit and I'd imagine it's a bear to install (never tried one myself).

You're using the stock pulleys with it.

 

You are doubling a very small contact area though (esp when compared to the contact area of a yoohoo belt). If you are reducing the overall tension on the alt belt like you said, then you may be seeing very minimal gains on the WP since there is only a small normal force acting on it to begin with 2 belts *(2*sin(~20 degrees)*T). Obviously its enough of a gain to work. *shrug* Now I really want to measure the tensions in these belts. I've gotta find the yoohoo tension to compare.

 

Anyone have pics running the yoohoo belt? How does it look?

 

Nevermind I juts found a "how to install" with good pics.

http://www.1300cc.com/howto/how2/belt.htm

 

No...The Yoohoo belt is a short v-belt put on the water pump and main engine pulley. It has to be pried in place and then cut to be removed. It's a quick and dirty hack to solve pump slippage...

 

well there is one situation where the yoohoo thing will have to work for me.

Building a car within the realm of "rules". I must use stock pulleys on my car, but i can remove emissions.