Underdrive pulley

[ViperPete]

hey all

I finally got around to installing my under-drive pulley that's been on my shelf for almost 4 years.

Anyway, once installed I notice that the voltage gauge dips from 14v to 12.8-13 or so when idling. At night with the lights on the gauges are dimmer than usual unless the engine is turning past 1k rpm.

The steering effort at low engine speed sometimes is heavier than usual.

I thought that with a smaller diameter crank pulley the accessories would spin faster?

Would a smaller pulley on the alt correct that problem? Or getting the alternator rebuilt to put out more amps?

 

[10-1=9]

hey all

I finally got around to installing my under-drive pulley that's been on my shelf for almost 4 years.

Anyway, once installed I notice that the voltage gauge dips from 14v to 12.8-13 or so when idling. At night with the lights on the gauges are dimmer than usual unless the engine is turning past 1k rpm.

The steering effort at low engine speed sometimes is heavier than usual.

I thought that with a smaller diameter crank pulley the accessories would spin faster?

Would a smaller pulley on the alt correct that problem? Or getting the alternator rebuilt to put out more amps?

This is the reason why I never liked the under drive pulley idea. A smaller crank pulley will turn everything slower not faster. Turning all the accessories slower will cause less drag/ parasitic loss of power at the crank shaft. Many peeps swear that slowing everything down will not cause any other problems but I don't agree. I like my AC cold & my lights bright so I never considered this mod.
If you put on smaller alt, ps & AC pulleys this will defeat any benefits of the smaller crank pulley.

 

[ralphie]

Mine does the same thing.....not a big nuisance, but it does happen

 

[earl lee]

This is the reason why I never liked the under drive pulley idea. A smaller crank pulley will turn everything slower not faster. Turning all the accessories slower will cause less drag/ parasitic loss of power at the crank shaft. Many peeps swear that slowing everything down will not cause any other problems but I don't agree. I like my AC cold & my lights bright so I never considered this mod.
If you put on smaller alt, ps & AC pulleys this will defeat any benefits of the smaller crank pulley.

Agreed, you have to ask yourself is that worth the extra 2 hp you might gain? UD's on modern NA motors dont make much sense. Todays engines are already far more efficient then what was coming out during the late 60's and 70's hell even the 90's where you would see a nice HP gain with changing out the pulleys to smaller ones for less parasitic loss.

Now on a supercharged car it is different. For example, putting a smaller crank pulley on my crossfire srt-6 will actually crank up the boost. Its easier to change out the blower pulley though so thats what I did but if I wanted more boost with the smaller pulley I can gain another 2 lbs to the blower but then I'd need bigger injectors and dyno tuning and im not going through all of that with my DD.

ViperPete what your experiencing is normal with a smaller underdrive pulley.

 

[Streetgliderx]

mine does exactly this,... idle for very long in a parking lot at night and you will have some trouble with the engine running too.... I assume its cause the voltage in the battery drops below what the computer needs to work properly. I figure ill just swap mine back to a bigger one when I supercharge

 

[ViperPete]

Hmmm,

Well then what I would like is a stock diameter pulley made out of aluminum or lighter somehow. So that I can have weight savings, and have normal accessory speeds.

 

[10-1=9]

Now on a supercharged car it is different. For example, putting a smaller crank pulley on my crossfire srt-6 will actually crank up the boost. Its easier to change out the blower pulley though so thats what I did but if I wanted more boost with the smaller pulley I can gain another 2 lbs to the blower but then I'd need bigger injectors and dyno tuning and im not going through all of that with my DD.

I will have to disagree with this statement. To up the boost you need to turn a belt driven super charger faster. To do this you need a larger crank (drive) pulley or a smaller blower (driven) pulley or both for maximum pressure. This always helps me to figure out how any kind of belt drive or transmission gearing works. Think back to when you were a kid with a 10 speed bike. I heard they have more speeds now but the outcome is the same.
Chain on the biggest rear sprocket will pedal easy to get up a hill but top speed will be limited.
Chain on the smallest rear sprocket will go like hell down hill. Going up hill will be hard to peddle.
On the front sprocket it is the opposite. Big front sprocket will give you speed but be hard to peddle. Smaller front sprocket will get you up the hill but limit your top speed.

 

[Streetgliderx]

yes smaller "drive" or crank pulley= slower acc speeds hence the reduced charging and reduced power steering flow

 

[rottenronnie]

We found out through back-to-back dyno testing that U/D pulleys are good for 8-10 horsepower on a Gen III. This stands to reason as you are slowing down water, charging and power steering pump flow (which includes our cooling fan).

Various sizes were tried before the final design went to the c.n.c. machine for production and sale.

A pulley with a 4.5" O.D. provided a decent compromise with NO increase in low r.p.m./low speed steering effort and only a minor electrical drop with ALL accessories turned on (high-beam headlights, high-fan, a/c, etc.) at idle, in Drive.
Keep in mind 1/2" O.D. either way is considerable.

That's what we found out so if you are looking to buy, maybe look for one that isn't too small unless it is a full-on race engine.

I no longer sell them.

And, as usual with performance parts... "Your results may vary"..:burnout:

 

[6speedquadcab]

8-10HP gain is correct.

 

[stealth78]

I had nothing but good things when I installed mine. As others already stated, you can actually gain about 10 rwhp! I never had any dimming of the lights either or any negative effects for that matter. If you are looking for a bang for the buck mod, I would personally recommend it.

 

[ViperPete]

I don't feel a HP gain really but I'm sure its there. Revs up a little quicker.

 

[NukeGM/Ford]

my lights are fine but the steering is a little heavy at parking lot speeds, no biggie

 

[earl lee]

I don't feel a HP gain really but I'm sure its there. Revs up a little quicker.

You own a Gen 5 viper, I dont think you can feel minimal HP gains after owning something like that and getting back into your slower vehicles. I know the truck prolly feels like a Hemi Ram compared to the viper.

 

[earl lee]

I will have to disagree with this statement. To up the boost you need to turn a belt driven super charger faster. To do this you need a larger crank (drive) pulley or a smaller blower (driven) pulley or both for maximum pressure. This always helps me to figure out how any kind of belt drive or transmission gearing works. Think back to when you were a kid with a 10 speed bike. I heard they have more speeds now but the outcome is the same.
Chain on the biggest rear sprocket will pedal easy to get up a hill but top speed will be limited.
Chain on the smallest rear sprocket will go like hell down hill. Going up hill will be hard to peddle.
On the front sprocket it is the opposite. Big front sprocket will give you speed but be hard to peddle. Smaller front sprocket will get you up the hill but limit your top speed.

Your correct, the crank pulley does need to be bigger. The blower pulley itself can be smaller or if you do the two in tandem a bigger crank pulley in combination of a smaller blower pulley equals more boost.

I was keying faster then my brain was thinking and got flipped up. lol

 

[stealth78]

my lights are fine but the steering is a little heavy at parking lot speeds, no biggie

How many ribs are on the belt? Some people were using a 6 rib belt due to the unavailability of a seven rib in the shorter length. In turn, at slow speeds the belt may slip a little on the power steering pump when the tires are biting into the pavement more.

 

[ViperPete]

You own a Gen 5 viper, I dont think you can feel minimal HP gains after owning something like that and getting back into your slower vehicles. I know the truck prolly feels like a Hemi Ram compared to the viper.

The difference between the Viper and my Ram is night and day. But I drive the Ram everyday and the Viper a few times per month so its not really a comparison for me. The experience is totally completely different.

The Viper is blazing fast and fun!
The truck is quick and fun!

Two different animals. And I can most definitely feel the difference in gains when I mod the truck- headers/TB/T56 etc.... I've been driving it for almost 6 years and put 30k on it. The Viper not even a year yet and only 4k miles.

The truck has evolved quite a lot since I first bought it and yet I still get big "doofis" grins when I row through the gears at WOT and beat a lot of ricers around town lol.

 

[NukeGM/Ford]

How many ribs are on the belt? Some people were using a 6 rib belt due to the unavailability of a seven rib in the shorter length. In turn, at slow speeds the belt may slip a little on the power steering pump when the tires are biting into the pavement more.

standard 6 that Tony sends with his pulley
how do you get 7 ribs to work, replace all the pulleys?

never really counted them before, all performance engines before this one had v belts

 

[stealth78]

standard 6 that Tony sends with his pulley
how do you get 7 ribs to work, replace all the pulleys?

never really counted them before, all performance engines before this one had v belts

My bad, I'm not looking at it... I thought factory was a 7 rib. So then if factory is 6 some people were using 5. Regardless of whatever the rib count, I know I was using one rib short as I also bypassed the AC pump to free up even more rotating resistance, by doing that the belt was so much shorter I could not find the proper belt so I ran it one rib shy. I still never had a problem.

 

[NukeGM/Ford]

My bad, I'm not looking at it... I thought factory was a 7 rib. So then if factory is 6 some people were using 5. Regardless of whatever the rib count, I know I was using one rib short as I also bypassed the AC pump to free up even more rotating resistance, by doing that the belt was so much shorter I could not find the proper belt so I ran it one rib shy. I still never had a problem.

i should probably get my lazy ass to check the PS fluid too, that could be it too

bypass the ac pulley really get you enough to make it worth while?? i would only do it at the track so not horrible to change the belt now that i have changed the tensioner and guide. is it enough to warrant the price of the belt ( which i have no idea how much they cost as i haven't had to replace one yet)