Underdrive pulleys [ merged 1/6/07]

[larryd]

Worth it or not? I'm thinking of going with the AEM tru-power pulley kit. Anyone used them?

 

[VOTBLINDUB]

I have heard that new underdrive pulleys will reduce strain on my engine and allow it to spin a bit easier. How is this achieved? If i do get the part/parts how many do i need? I hear a good brand for those is unorthodox, any other good suggestions? If i do get that done, what are drawbacks of going aftermarket in that department? What do you need to expect from that? Does it drive different, does it sound different, in general will i see, feel, hear a difference? what is the impact on performance? How long do they last? is it legal to do it? I am trying to find out as much information on this topic as possible before i do anything to my car. I'm also looking for information on them in the long run, will there be side effects from puttin in upd's? thanks for the replys!

 

[ChvyKc]

The thought behind the underdrive pulleys, to what I understand, is that they are lightened and they change the size of the pulleys to put less stress on the motor to turn them. I have heard of people having problems with underdriving the crank, I am not for sure what type of problems they are having or if this is even true.

The only difference that I can feel between the stock and underdrive pulleys on my 3G GT is it seems to be a lot smoother and a little faster. There is no difference in the way that it drives or the way that it sounds.

David

 

[a351must2]

Underdrive pulleys just spin the accessories slower, like the alternator, A/C, and maybe the water pump. It just reduces the HP required to spin these parts by turning them slower. The problems you "may" run into are poor charging at idle or overheating due to poor water circulation. I don't know if either of these problems happen in DSMs, but they do in some other cars...i.e. pre-79 or so Mustangs that came with an externally regulated 35amp alternator that could barely charge at idle with a huge crank pulley do not charge at all at idle with an underdrive pulley.

 

[Soular]

I have one on my 96 NT-MT It is, By far the best mod that I have done.

First the BAD.

It can be a bear to install. But follow the directions and heat the new UPD in the oven you ill be fine.

You will lose some voltage due to the lower RPMs

AC will not blow Cold air until you hit about 2800 RPMs

Power Steering is Firmer due to the lower RPM of the Accessories
(Good to me Bad to some)

Remembering the non-stock belt sizes is a pain..

THE GOOD:

Car Idles firm at 800rpm

@ 65 MPH RPM is at 2500 not 3000 which = Increase Fuel Econ.

The Car Runs at 500 less RPM then Stock which stress the motor less

AfterMarket Exhaust Noise reduced at cruise speeds

The Car Feels Quicker and is Quicker...

Power Steering is Firmer due to the lower RPM of the Accessories.

This is a good Mod

I have the Howell (sp) UDP

I want to get one from my GSX but I think that is where you run into major issues since the Pulley in the 4G63 is also a Harmonic Balancer which is not the case in the 420A

I hope that helps -Chris

 

[Enigma_Man]

Originally posted by Soular

The Car Runs at 500 less RPM then Stock which stress the motor less

BZZZZZ!! wrong!

Your accessories will be running at a percentage less rpm than they used to, but the engine speeds are unchanged completely.

The only thing an underdrive pulley setup does is to turn the accessories slower, by fitting different sized pulleys onto things. Generally, you will see 5 to 10 horsepower increase, due to less drag from the accessories. On our cars, you can get 5 or 10 extra horsepower by just turning up the boost a tiny bit more (if you can). So, it's probably only really worth it for those who are really pushing to get every last horsepower out of their car, or just looking for some nice bling for their engine bay

-Jesse

 

[doug]

http://dsmtuners.com/forums/showthread.php?s=&threadid=2580

http://dsmtuners.com/forums/showthread.php?s=&threadid=114

 

[Soular]

Maybe I should clear that part about the < 500 RPM Thing

The Ratio I'm talking about is Speed to RPM.

The car is working less to make speed now.

At 65 see what your RPM is I'm sure it's around 3000 with stock 16's
After the UDP you will see a lower RPM post UDP install on and NT.

But old boy is right about the motor working at the same speed.

The lower idle (800) seems to be a result of the ECU trimming the car since it's spinning things slower.

Maybe all NT idle at 800.. if that's the case the UDP has nothing to do
with that.

I hope that clears things up. It's a great mod!

P.S. Thanks for the Links D!

 

[BD1]

Woe to those that undergo this project. By the end of the weekend the whole project will have cost me 230 dollars and about 7 hours of my time.

Good modification, do not try to do it on your own though. Like everyone else has been saying, the UDP is smaller than the stock pulley, so it turns everything slower, b/c it can't do as much work, so it gives the power lost from the accessories to the engine.

 

[BD1]

Originally posted by Soular

Maybe all NT idle at 800.. if that's the case the UDP has nothing to do
with that

I idle @ 1100 in cold weather after a startup and 900-1000 after I begin driving.

 

[psychlow]

Maybe I should clear that part about the < 500 RPM Thing

The Ratio I'm talking about is Speed to RPM.

The only thing that changes RPM in relation to speed is regearing.

Underdrive pulleys have no effect on how fast your engine runs for a particular speed. There will be less stress on the engine, but it'll be the same RPM.

 

[Soular]

Again you guys are right about the science with the RPM/Speed Ratio.
True Gearing will change the top speed achievable in Gear X

But what I'm reporting is fact. These results are a direct relation to the
install of lighter, smaller UPD.

My NT along with my friends NT both exhibit this behavior. Which is a
change from how the car performed before the UDP. We both notice
a drop in RPM at speed.

Again let me qualify this by saying this was 5th gear performance. That's what I meant when I said at cruise speed.

We think that this is do to the lightweight of the UDP. It is way lighte
then the stock unit. And way smaller. Not sure what the ratio is. And as
stated by others, nothing has changed in the motor or gearing. The
motor is working at the same speed… the UDP is not changing that fact.

Our best guess is that since the parasitic effect is reduced on the engine,
The engine works less at speed. Rotational mass reduction seems to
allow the car to work less to produce speed in 5th gear. But I would say
the motor seems to rev faster. Again this may be due to the reduction in
mass of the UDP.

Those with stock pulleys will report that at 65MPH RPM is at ~3000 and
85MPH RPM is ~3500 With the UDP 85MPH is about 3100RPM.

One things is certain... if everything else I said is BS.. you will
Increased fuel ECON. That is for sure!

As for the time it took us to do this mod. It took about 4 hours. You
have to Lower the motor and pull the stock unit off which can be a
beast. Remove belts… stuff like that. If you heat the new unit, it slides
right on without issue. Button the car back up and you are done.
Again... this is one of the best mods out.

And if you have a high power sound system... generating electric power
is really not an issue. Lights may dim if you have your system boom'n
while running the AC with your Hi-Beams on while the car is at idle

Good Luck

 

[DSMSpyder99]

the only underdrive pullies i would get is the Buschur Racing because they are harmonically balanced

 

[rookieupgrade1]

Under drive pully WILL NOT change the your final drive gear ratio at highway speed. Maybe you all did something else that caused the discrpincy.

To change your highway speed RPM you have to either change the trans gearing or tire size.

The tach is electically driven so maybe the loss in voltage caused the differance.

I know my Lasers tach is 500 rpm lower than the engine according to the pocketlogger.

Underdrive WILL allow the rpm to climb faster due to the reduction in the amount of drag applied to the crank by the accessories.

Thnk about the relation between the crank and trans. How could the accessory belt pully (UDP) possibly effect your RPM at highway speed.

Come on people think a little.

 

[Soular]

Hey G,

Again the science is correct... you are dead on... But this is what my car is doing. I also have a datalogger and it reports the lower RPM so your theory about reduced power seems like a good explanation to me.

Maybe the ECU is running at lower power levels and sending out false info.

But I will say again on the Stock 16 the car runs at a lower RPM in 5th gear. 65MPH is under 3000 85MPH is ~3100

I have had 3 different tire sizes on the car since doing the UDP and everything seems to remain consistent
with my findings.

If you have a UDP then and your stuff has remain running at stock numbers then cool. Then that’s what
You have to report. My car along with another NT have shown a reduction in power output needed to achieve
a said speed in 5th gear.

Fact is results may differ depending on your car I guess. All I can do is report my findings.... Regardless this is a great mod! Well worth the money!

If you want true facts these guys would know.. http://www.howellautomotive.com/howell/store/Catalog/Catalog/

The pulley is the AF/X 30% Underdrive Pulley 2.0 Diamondstar

http://www.howellautomotive.com/Howell/Store/catalog/catalog/product_info.php?products_id=298

If you email them they can tell you can expect from their product.

Good Luck!

Originally posted by rookieupgrade1
Under drive pully WILL NOT change the your final drive gear ratio at highway speed. Maybe you all did something else that caused the discrpincy.

To change your highway speed RPM you have to either change the trans gearing or tire size.

The tach is electically driven so maybe the loss in voltage caused the differance.

I know my Lasers tach is 500 rpm lower than the engine according to the pocketlogger.

Underdrive WILL allow the rpm to climb faster due to the reduction in the amount of drag applied to the crank by the accessories.

Thnk about the relation between the crank and trans. How could the accessory belt pully (UDP) possibly effect your RPM at highway speed.

Come on people think a little.

 

[VOTBLINDUB]

Thanks for lots of input to everybody! Is there a way to spin my alternator the same or a bit better with aftermarket UDP's? I am going to compete in the coming summer in sound competitions so i need lots of current going or at least as much as it can do. I am planning on a second battery in the trunk. Does anybody know how i can still keep my current at it's highest and get the powerboost you talked about? The A/C doesnt matter much to me, i drive with the windows down in the summer, i dont care, i dont drive many ppl with me, if they go in the car, it's their problem then, not mine.

 

[jérôme]

i have a crank pulley, its not really the best mod at all, just kinda gives me the peace of mind that ive taken stress off the engine. car picks up a little quicker.. though it seems like you need to hold onto your clutch a little longer(less rotational momentum) when you are starting.
j

 

[LikeUnoSheit]

bla bla bal rpm is lower. THe pulley makes no difference to rpm. THere are some benefits, but on an unbalanced engine i want the harmonic balancer there. Buscher dis have a great one available (had some probelms with continuous production last i checked). Currently running a part time squeaker till i find a solution or produce my own. Ive gone through 3 stock pulleys, sisters is goin out also. Stock sucks, buy better. Prothane motor mounts vibrate my ass enough in the car, no need to go without the balancer to make the interior fall apart. If i wanted a ride that bad I'd be driving a Harley!

 

[CR95GST]

This crank pulley reducing RPMs is 110% total BS. The one and ONLY thing an underdrive pulley does is reduce the parasitic drag on the crank. It has the same properties of physics as adding a lightened flywheel. It may "free-up" some HP allowing for slightly quicker revs. In no way though does this have any direct relation to the gearing of the car. The crank is turned by the combustion pushing down on the pistons. The crank then turns the flywheel, which then turns the transmission by means of a clutch. The transmission has a series of gears which turn the differential which then turn the axles and finally the wheels. The ONLY way to affect RPM/MPH is to change the overall wheel/tire diameter or the gearing in the differential/tranny. Why would TRE go through the trouble of manufacturing a taller 5th gear set if all they had to do was add an underdrive pulley? Riddle me that Soular.

 

[psychlow]

Holy dead horse, Batman!

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[purpleesi]

this may be a stupid question, but if i got an underdrive pulley could i still keep my big stereo, or would it be useless?

 

[BUCK]

Frankly with a big stereo you need an OVERDRIVE pulley - you know the answer to this already!

 

[Eclipse96Ryder]

i got an UDP and power a 600w kenwood amp, kenwood deck, and a 10" bazooka tvb-141, and it seems fine to me

 

[BUCK]

Obviously I need to can those Subwoofers & get a Bazooka - I need a 120 Amp Alt & a 1/2 farad Cap to run a 400W Sony Amp...

 

[Mike1992]

I bought a UDP tonight and if/when I do put in a system, ill just a a .5 farad cap

 

[Eclipse96Ryder]

um, i dont use a cap, my battery goes dead every 5 months tho, haha. But my shit sounds real nice and hits harder then a lot of peoples two 12's