- Jul 27, 2021
- Reaction score
- East Texas
- My Car
- 1971 Mustang Mach 1 M code 351 4 speed
You wont get 20 HP, but when I used to do 5.0 Mustangs in the 80's and 90's the underdrive pulley sets were one of the most popular performance accessories around. You could definitely feel a difference when you installed them, but they would underdrive everything, not just the PS pump. I think I was dyno tests back in the day about the pulleys and I don't believe they made a ton of power, maybe 6-8 HP, but it was across the board, meaning they were making 6-8 HP across the entire RPM range, and not just at the top of the RPM range. It certainly made a difference. On manual transmission cars they were fine to use, but automatic transmission cars in traffic tended to overheat, not charge their batteries, and the A/C did not work well while you were stuck in traffic.So I'm not going to gain 20 HP by under driving my PS pump?