Underdrove Pulleys: Myth?

[Butters]

I'm just curious, how much is to be gained from underdriving the crank. I've read a few articles, but it seems like its more of a ricer myth than a proven performance upgrade. What do you guys think... how much if anything can be gained from underdrive pulleys?

[MustangEater8251]

ITs good one some cars, I noticed a gain on my 3.4L but on the 3.8L I heard the gains are barely noticeable...

[White95]

On my 3.4L, you can feel the difference in the low end

[Freeser]

Yep I also noticed a low end gain.

Matt

[StudlyCamaro]

i didnt notice **** when i put my underdrive pulley on my 3.4L , and i also took out the AC at the same time, but who knows it might have helped

[Devilsy2k]

Did you guys use your stock serpantine belt when you put your crank pulley?

[Butters]

So is this little gain simular to a CAI type gain? Has anyone ever seen dyno results or ET's that prove if the pulleys help?

[5_spd_pewter_v6]

i'm not sure the 3.8 has an underdrive pully.

[JoshMcMadMac]

Here is one way to think about it. Removing certain components from the pulley system all together DOES help. Running the strip without PS, AC, alternator, saves a few tenths. Now an underdrive pulley improvment is going to be worse than without the belt, but better than stock. You are gaining little, but also losing little. However, if the pulley ratios are not maintained properly, you will find yourself underrunning the alternator and create charging problems. It is necessary to do some simple math when considering pulleys different than stock. It is simple ratios; take it for what it is worth, my 2¢.

[kerist]

I too have the pulley kit from AMMP for my 3.4L, but I am not waiting to see anything more than 5hp at the fly (if that). the import market offers a set of lighter alloy pulleys rather than just an underdrive. The significantly lighter pulleys allow the engine to spin more freely (eliminating rotational mass).

I feel that a light-alloy set of underdrive pulleys would be a nice aftermarket piece for the 3.4L.

kerist
3.4L miata!

[Ian]

think about that "lighter pully" theory.

how much rotating mass does a crank pulley have? have you ever felt a crank pulley? they weigh at most 1.5lbs. for every 10lbs of rotating mass you remove in the drivetrain assembely, you gain .1 on the track. lets say you manage to make the crank pulley weigh 1lb instead of 1.5 by using aluminum. you just saved .5 lbs in the rotating drivetrain. this would save you .005 at the track.

just a little math breakdown for you.


oh, and yes, underdrive pulleys do work. 'lightened' underdrive pullies are a ricer mod, if thats what you want to call it.

[White95]

Originally posted by Devilsy2k:
Did you guys use your stock serpantine belt when you put your crank pulley?

I had to buy a shorter belt, I forget how much shorter thought. I bought mine from American Muscle Motorsports and they told me the correct belt size.