i dont get it. If you talk to a lot of people, they'll tell you that underdrive pulleys are awesome and will add power. But when you tell people that you have removed pulleys (i.e. smog pump and a/c) people say "big deal" you might have gained a little, if not anything. whats up with that noise? isnt taking extra loads off the engine(especially on a serpintine system) supposed to add power? A 305tbi with a/c runs a 90" belt, but if you remove the smog pump and a/c you run a 50" belt. Shouldnt that make some kind of difference? This topic is driving me nuts!can someone give me some answers?

 

fresh from the factory the accessories took very little power away from the motor. The A/C even took less than a horsepower away (if that tells you anything about how much the rest of the accessories took away). Over time these accessories cause more and more friction though, which means it takes more and more horsepower to turn it.

When you remove A/C or your Smog pump, all that you're doing is getting rid of old equipment. If you put a brand new SMOG pump in it's place, you'd see almost the exact same "power boost". Same would go for the A/C .

The people who go "oooh" and "ahhhh" when you say you have under-drive pullies are just misinformed and dont understand what is really going on.

 

Underdrive sheaves have two problems.

First, they don't do much to unload the engine except for the water pump. If you really want to free up some power, install an electric water pump. The alternator electrical load determines the resistance to turning, and when they are turned even more slowly, they not only create a bit more drag from lowered efficiency, but heat more due to less cooling air flow from a slower front fan. The sellers of these sheaves realize that some of use have finall caught on to the problem, and will gladly sell you an undersized alternator sheave, at an additional cost, to "correct" the speed. That only forces the belt to flex beyond its designed minimum bending radius, which allows them to sell you more belts. The power steering pump draws almost nothing unless the wheels are being turned or the pump is bad. And whne you turn the wheels at a lower pump speed, you aren't going to get much assist.

The other big problem with aluminum sheaves is wear. Underdrives might not be so bad if they had steel rings for belt sheaves, since the aluminum wears away much faster, but the aluminum wear surface only compounds the lower efficiency of the accessories due to belt slippage.

Ideally, a set of sheaves would have lightweight hubs, be at a standard diameter, and have a much harder wear surface, like steel. The really good setup would be pure titanium sheaves, but no one would spend that much for no power gain.

 

Uhmm, the hi-zoot pulleys should be hard anodized. Also the pulleys make a bigger difference depending on the size of the engine. We put some pulleys on a 2300 cammer mustang and thought we added a blower. (or maybe not, but the difference was huge). Back in the day some 4 banger manufacturers actually limited things like oil pressure to save HP. (kinda scary).

 

Removed AC and Smog
Underdrive Crank and Alternator Pulleys


Made biggg difference for me