Installing the Underdrive Pulley

[FLATOUT]

I never noticed any issues with the comp coupe version on my Gen 4, or the comp coupe pulley on my gen 3. Put the ipsco on my Gen V a couple weeks ago and no issues.

[Jack B]

The stock pulley only weighs 1.12 lbs?

I weighed mine a couple weeks ago and IIRC it was a pound or so lighter than stock. Fairly significant difference.

Also, I read that the lower RPMs on accessories might be an issue. I have see no difference in alternator voltages, and the AC blows as cold as it always has.

[Steve M]

is there a weight differance beteween the pully's?

It wouldn't make much of a difference if there was - the gains from this mod are from not spinning the water pump, alternator, and PS pump as fast, not from weight savings.

[FrgMstr]

1lbs 13oz Stocker, 1lbs 1oz on the IPSCO IIRC.

The weight is not that big of a deal, but sure does not hurt. The diameter of the IPSCO pulley is smaller therefore allowing the engine to do less work to turn all the accessories in a revolution on the crank. But therefore the accessories spin slower.


2014-05-15 15.58.53.jpg

The stock pulley only weighs 1.12 lbs?

[ViperGeorge]

If this is such an easy HP gain with little to no adverse impacts why didn't the factory decrease the size of the stock pulley?

[Jack B]

Because of the 1% that live in death valley.

If this is such an easy HP gain with little to no adverse impacts why didn't the factory decrease the size of the stock pulley?

[Snakebit10]

In the past I have done the underdrive pulley mod on a few of my cars. I had a decently high wattage aftermarket sound system in one of them and the underdrive pulley didnt work well with it. If I sat at idle too long with music running, even low, you would see the lights start to dim a bit. When you revved it got brighter. I would say if you are totally stock, sound system-wise you should be fine. The cars I had them on that were totally stock electronically speaking did not have a problem at all.

[Back In Black]

If this is such an easy HP gain with little to no adverse impacts why didn't the factory decrease the size of the stock pulley?

Actually they did...on the ACR-X. To decrease water pump cavitation at high rpm.

[FLATOUT]

Actually they did...on the ACR-X. To decrease water pump cavitation at high rpm.

Comp Coupe as well, same part number from Mopar.

[Voice of Reason]

My IPSCO pulley came in today. It's been said before but I'll say it again, it's a beautiful piece!

[FLATOUT]

Very nice!

[Voice of Reason]

I just finished installing it and it couldn't have gone easier. I think I spent half the time removing/replacing the belly shield.

One note for the next person doing the install - my idler pulley bolt was 15 mm not 19 mm as in Jack's OP.

[Voice of Reason]

I put about 100 miles on it yesterday, I'm wondering if it doesn't need a belt that's 1/2-1" shorter. Taking off from a stop there were a few times where I heard it or the idler pulley chirp for a second. Each of those times I gave it barely enough gas so the tach really dipped low before I started moving. After making sure I gave it more gas I never heard it, but it makes me think that a shorter belt would give it either slightly more wrap around the pulley or (and I think this is it) the tensioner isn't "tensed" to the same point now, it's a little looser. A shorter belt would put it back where it was. If I continue to hear any chirping I'll experiment with shorter belts.

[Snakebit10]

I put about 100 miles on it yesterday, I'm wondering if it doesn't need a belt that's 1/2-1" shorter. Taking off from a stop there were a few times where I heard it or the idler pulley chirp for a second. Each of those times I gave it barely enough gas so the tach really dipped low before I started moving. After making sure I gave it more gas I never heard it, but it makes me think that a shorter belt would give it either slightly more wrap around the pulley or (and I think this is it) the tensioner isn't "tensed" to the same point now, it's a little looser. A shorter belt would put it back where it was. If I continue to hear any chirping I'll experiment with shorter belts.

The cars I've put in on in the past always were reccomended with a smaller than stock belt. Check the companys website in case they have that kind of info. The company in Long Island had that info when I bought the pullies. Its not hard to figure out though if they dont have that info. Depending on how far your tensioner can adjust you may have to go with the smaller belt if you keep hearing some slippage.

[FrgMstr]

I put a new stock belt on when I installed mine. Not issue one after a full day of racing on Sunday.

[FLATOUT]

I have put some hard spirited runs on my car as well with the pulley and haven't heard a chirp yet. If we could figure out a smaller belt that would fit I would gladly swap to it though. I know that the smaller belt that they went to on the Gen 3's will not fit our cars.

[Jack B]

There was more than enough tension with the old belt and new pulley.

I have put some hard spirited runs on my car as well with the pulley and haven't heard a chirp yet. If we could figure out a smaller belt that would fit I would gladly swap to it though. I know that the smaller belt that they went to on the Gen 3's will not fit our cars.

[cashcorn]

I still question this mod. I want to believe the SRT engineer's would have figured this out. Even so, at max 10hp. Is this even a measurable gain? just asking..

[Shooter]

I still question this mod. I want to believe the SRT engineer's would have figured this out. Even so, at max 10hp. Is this even a measurable gain? just asking..

It's a 10 RWHP gain, and that is a pretty good return for your money...especially on a Gen 4 or Gen 5 Viper.

[IndyRon]

It's a 10 RWHP gain, and that is a pretty good return for your money...especially on a Gen 4 or Gen 5 Viper.

Actually its not. If anything it is maybe 3-4rwhp, well within variances between runs. I wish it was 10rwhp...I have the IPSCO on my car as well but it just isn't.

[FLATOUT]

Actually its not. If anything it is maybe 3-4rwhp, well within variances between runs. I wish it was 10rwhp...I have the IPSCO on my car as well but it just isn't.

We saw 12 on a local car SAE so he was quoting conservative estimates from that dyno lol. Every car reacts different.

[Jack B]

Although the hp gain is debatable, the gain follows the entire hp curve, therefore, it is consequential, especially when you look at a 1/4 mile run. Next, we have to define consequential.

Actually its not. If anything it is maybe 3-4rwhp, well within variances between runs. I wish it was 10rwhp...I have the IPSCO on my car as well but it just isn't.

[IndyRon]

Although the hp gain is debatable, the gain follows the entire hp curve, therefore, it is consequential, especially when you look at a 1/4 mile run. Next, we have to define consequential.

My definition of consequential must be different than your definition. Show me a graph of it following the entire curve and to what extent as you stated. My dyno runs did not reveal those gains. When dyno runs vary 2-3 hp or more due to timing advance, drivetrain temperature, IAT's, and fuel trims, not sure how you can say 3-4hp is really consequential. I think the 12hp run was a fluke. If a couple more people spend the money on the runs like I have and prove it gains 10-12, I'll change my tune. I'd just hate to see someone expect $15/hp on this mod.

[Jack B]

You missed my point, the HP gain is debateable. It cannot be debated that there is a gain across the entire HP curve.

My definition of consequential must be different than your definition. Show me a graph of it following the entire curve and to what extent as you stated. My dyno runs did not reveal those gains. When dyno runs vary 2-3 hp or more due to timing advance, drivetrain temperature, IAT's, and fuel trims, not sure how you can say 3-4hp is really consequential. I think the 12hp run was a fluke. If a couple more people spend the money on the runs like I have and prove it gains 10-12, I'll change my tune. I'd just hate to see someone expect $15/hp on this mod.

[IndyRon]

You missed my point, the HP gain is debateable. It cannot be debated that there is a gain across the entire HP curve.

That I will agree with...though that wasn't your original point...the original point that you made was that the gain was "consequential". I've just not found that to be true...and as I said before, I'm running the pulley on my car.