Under Drive Pulleys

[Rock Chalk]

What are the pros and cons of underdrive pulleys and who makes good ones?

 

[Casey]

Check out the new product section, you are right on time!

 

[GTSnake]

So how does it make 15rwhp? Is it lighter?

 

[joe117]

It doesn't drive the accessories quite as fast. That saves some hp.
15hp? I don't know, could be.

 

[Anthony - 98 GTS]

I got a solid billet, fully polished set from March Performance. These are stock sizes and I used a custom crank under drive pulley.

 

[Torquemonster]

Pros are they take less power to drive and look real sharp.

Cons - not so good if you do a lot of slow idling around town - might drain the battery if lights are on and air con is on full on a hot night, idling around Vegas for a couple of hours....

Most people find it no problem keeping the battery charged with under-drive pulleys.... if your lights start going dim cruising the interstate at 1500rpm one night - go down a gear or two and keep the rpms up for a while to recharge.

 

[WESTCOAST JASON]

They make 15RWHP because in the end, the alternator, power steering pump and water pump are all causing less drag on the motor. If you get a chance, check out a picture of a GTS-R with the hood off. The power steering pulley is HUGE, I mean like a small pizza huge. There is risk of a battery light if you say were idling with the high beams on and the heater fan on full. The design is to keep this from happening though and if the light were to flicker on, a quick burp of the throttle could stop it. (this is theoretical, I have not had the light come on in this situation)

 

[BadVenm]

Jason,

I'm waiting for an answer to my e-mail eailer today about your new under drive pulley's. Hurry up bro, an order may follow quickly!

Thanks.

 

[Snakester]

I don't know about the underdrive set posted in the New Products section, but I had underdrive pulleys on a Mustang before and the charging would drop down at idle. The battery kept charged OK, but the headlights would visibly dim at a stoplight, and then get bright when you accelerate from a stop. This had the effect of looking like you were flashing your high-beams when taking off from a stoplight at night, and ********** many people when I drove the car. Plus it was embarassing to have the lights dim and brighten, like there was something wrong with the car.

All for a tiny gain in HP.

Of course I don't know if the alternator charging system in the Viper is that finicky, but the unavoidable downside is the typical "Viper tax" with the Viper underdrive set being $400-$450!, as opposed to $100 for other cars.

In fact I had read somewhere that one of the larger underdrive pulley manufacturers have alumunum pulleys for Dodge trucks that will bolt onto the Viper for something under $40, with 3 different sizes (percentages) available.

-Dean.

 

[Sam 01 RT10]

Looks like I'll be the test mule for them here in Vegas.
I drive the car 2-3 days a week, and it will be driven w/lights on and A/C blasting. If you wait 'till summer, I'll report back. They should be here next week.

 

[joe117]

Be careful who you order from. There have been some unresolved complaints on other threads.
It always pays to check things out. After you order, if things don't go right, you could be left with no recourse but to pound sand.

 

[Tom F&L GoR]

My '94 has a 5.9L underdrive pulley, about $50, and the new belt is about $25. It's only 5 rib instead of 6, but after 50K miles, that's not a problem. With lights and fogs on, AC on, things dim, but nothing to worry about.

Helps with autocross power steering pump problems- it's not running as high a pump speed.

 

[WESTCOAST JASON]

There are no 'cheap' underdrive pulleys for the Viper right now. The material and labor cost on just the crank pulley is over $100 and then it needs to be anodized. When I first started trying to find a cheaper alternative to the $695 set sold by another shop, I found out that even making them ourselves, it is costly. This is apparent when you see them, the only steel ones available were for the alternator. We wanted a gorgeous matching set, and that is what this is. There is no Viper tax on these. I am personally ANTI-Viper tax. I have daily driven a Viper since 1997 and have paid more than my fair share of Viper tax.....

 

[Tom F&L GoR]

With part numbers like these, how can you go wrong...

http://www.rpmoutlet.com/dramasp.htm

Belt for a '94 with this pulley is 25-060760, Gates K060760 or AC Delco 6K760.

 

[Jack B]

Jason:

Could you give us the pro/con for your set versus the 69.95 pully from Tom's post.

 

[WESTCOAST JASON]

I have no idea what ratio the single pulley for the 5.9 would put the accessories at, so I can't answer the question. We would love to dyno test one of those though to see what it makes. (and to oviously test for all the other pulley stats like charging, etc.) I am always open to new products (obviously) and look forward to learning more about the possibility of getting by with a single pulley. I know that the GTS-R program used a full set like ours as opposed to a single unit, and this allows better 'tuning' of the accessory speed. (as opposed to a single % change across all accessories)

 

[ViperJoe]

So Tom are you talkin just the crank pully for the 5.9?

How involved is it to do this on a Viper, or is it a simple bolt on?

Thanks

 

[Tom F&L GoR]

First, it's the $69 pulley without the damper, as Jack points out. The advertisement doesn't mention it's also for a 5.9L (shows 5.2L) until you go to the installation help page. Second, I was running on empty brain when typing and thinking at the same time; the replacement pulley is 6 ribs instead of Viper OEM 7 ribs. The website lists this as a 25% reduction pulley, so I assume that means the diameter of the new crank pulley drives all the accessories at 25% slower speed. (Looks like the $118 kit has various pulleys to reduce different accessories by different amounts.)

It attaches to the OEM Viper damper using the small bolts that the Viper pulley does. The idler pulley is spring loaded, so there is no other wrenching needed. Very simple.
http://www.rpmoutlet.com/ins504500.htm

 

[ViperJoe]

Anyone care to try this cheap(er) mod on a GEN2 first?

 

[Jack B]

I have it on mine, like Tom said it goes on easy. As far as hp gain I cannot tell for sure since I put on T&D 1.7's at the same time. I can tell you this I showed a peak hp gain of 20-25 hp and a showed an improvement of over 50 hp at one point on the the hp curve. Once again this is with the T&D's and the pulley. This was not a one time comparison I have approximately 75 pulls on this engine, about half before the change. I show an average 460 hp (NA)with this setup.

 

[Snakester]

Jack,

Have you noticed a visible dimming when the car is at an idle?
I'd be happy to swap the belt and pulley for that low of a price IF I knew that the lights wouldn't dim and brighten between idle and driving speeds.

-Dean.

 

[ViperJoe]

Jack did you go with just the 25% crank pulley or the set of 3 pulleys that was on the link?
Thanks

 

[Jack B]

I am using the single 25% pulley. I have not noticed the lights dimming any more than the stock setup. You have to remember that the eye can see a 1% change in voltage so even with the stock setup there has to be some variation

 

[joe117]

"the eye can see a 1% change in voltage"
That's an interesting statement. Is it true?

 

[ViperJoe]

He probably meant that the eye can see the difference in light output that a 1% change in voltage would produce.

 

[joe117]

Well, I figured he was talking about the change in brightness caused by a 1% change in voltage.

I'm not sure of myself on this but that never stopped me before.
I'd have to say that I don't think one could detect the change from a 1% voltage change.

Just for drill, let's say the lamp draws 20 Amps at 13 Volts. That means the filament would be .65 Ohms and the power consumed by the lamp would be 260 Watts.

Now we raise the voltage to 13.13. The lamp now draws 20.2 Amps with a power of 265.23 Watts.

Can one detect that increase in power?
I'd say no, but I'm still not sure.

 

[Jack B]

Power quality consulting is a large part of what I do for a living. The phenomenon is called flicker. The eye can detect movement greater than 1/32 of a second and a voltage change of 1% or greater. Take a 120 volt lamp and change the voltage 1.2 volts and the eye can see the change. Basically if it is electrical in nature I can fix it or tell you how to.

 

[joe117]

I'll take your word on the 1%.

But the speed thing,
How about movie projector at 16 frames/sec? Or a TV at 1/30sec?

 

[Snakester]

Movies are 24 frames a second, and TV is 60 frames a second.

 

[joe117]

Yeah, I guess it is 24 and 60.