I was surfing the Paragon site and ran across a pulley underdrive set they're selling.

Does anyone run this, or have experience with it? The idea of having accessories be less of a leech is attractive, but don't want to run into other issues.

~C

 

You should also quantify the power savings you get as well. The 944 manual state that the air-con draws 40-watts. That's about 0.05hp.

Then the power-steering doesn't really draw anything until you start turning the wheel.

The alternator provides as resistance in proportion to the load. Let's assume a meager 50% conversion efficiency. So you've got all your lights on full (200watts) and the big boom-box stereo blasting away (500watts). Add about 200watts for other electrical needs and we've got a total of 900watts consumed. Multiply by 2x for 50% efficiency and the alternator is drawing 1800watts from the engine. That's 2.4hp

So the total draw of the accessories is about 2.45hp at full load. Assuming that the underdrive pulleys gives you a reduction to 75% of normal speed, we're talking about a savings of 0.61hp! It'd probably be a better use of your time and money to look elsewhere for mods...

 

Wow... your very excellent explanation shows why this mod isn't seen in very many (any?) signatures...

Thanks Danno!

~C

 

underdrive pulleys free-up hp in two ways -

first is by slowing down the speeds of the accessories by using a smaller diameter crank pulley- waterpump, steering pump, alternator, a/c sometimes. The second way is that usually the actual accesory pulleys themselves are also replaced with lighter weight units - just like the effect of a lightened flywheel.

Between the 2 you can get dramatic results which manifest in quicker revs and torque gained. I have them on the M3 but the main gain of that unit is b/c the 12 lb harmonic balancer is replaced. I don't think you will see 15-20 hp, but 5-10 is resonable.

Eugene

 

I did the pully reducion to an RX7. This allowed the shift RPM to increase without causing water pump cavitation and altenator damage. If you are doing this to increase HP, well the increase will not be much. Danno is correct, the gains are small.

The 951 isn't a hi-rev machine so I don't see a need for this modification. The RX7 lives to be rev'ed.