The findings are in:

You can make $$ from selling these things.

http://store.webbmotorsports.com/ind...0447abd008b999

 

I got a probably obvious question then. That means that a 17% will make 7-8 more horsepower than a 15% pulley, right?

 

I have a 3% crankl pulley I would like to sell. Low milege I just made some changes to my car and decided to go another direction. I also have a 0% pulley.

Either pulley I will let go for $100 each plus shipping ( probably $5-$6 )

 

Roughly...But lately the reccomendation is to a 15% pulley and a 2% crank pulley to achieve 17%.

 

No, more like 2-3HP - you are only adding another 2% vs. 15%, so if you get an optimistic 15HP from a 15%, you might get 2-3 more HP from a 2% crank pulley. The arithmetic isn't linear, but pretty close.

And that's why they sell them, regardless of whether they are good engineering...

 

There's a very thorough evaluation and discussion of the crank pulley in Randy's forums that covers all the topics on this thread so far.

http://store.webbmotorsports.com/for...opic.php?t=707

 

I'm going by their math. If you make the jump through the link, you'll see that they're claiming 7-8hp on the later cars when adding a 2% to a 15%. I'm just wondering if the 17% will make 7-8 hp when compared to a 15%.


I'm going 17% because a 2% crank pulley would cost me 5 belts anyways. Now if I changed every year, that would be 5 years before I recooped the cost. Plus I don't like this shuddering that people are getting at low revs. That by itself indicates to me that something is wrong.

 

So, what I understand is 7-ish hp gained from a combination of faster sc spin and less parasitic loss from the crank.

Mine (+2% crank) goes on this weekend. I'll post impressions that I get (sans dyno) afterward.

dan

 

So theoretically, a 17% alone would have a greater increase in hp since it doesn't have the 2% overdrive on everything else.

 

The reason to want to use a 15% and 2% together is to lessen the need to change the serpentine belt as often. Reading online has shown that when using pullies smaller then 15% can eat up belts faster.

 

Yea, but I haven't heard of people snapping belts often as in fewer than 10k miles so.... the logic still stands that I could have 5 years worth of belts for the price of a pulley without the shuddering that people are experiencing at low RPMs.

 

I see your point. I need to do some searches to when the belt problems occured.

 

I haven't had any problems with these, and we've done over 100 now. We have them on ALL of the race cars as well. Our initial test car now has over 40K on it.

As for the 17% making the same power - it doesn't work that way because the powergain from the 0% crank pulley is giving you a gain. The 2% is giving you that gain plus the additional boost.

We've seen the best numbers on the dyno from the 15% pulley using the 2% crank pulley - that includes 17% and 19% pulleys with different crank pulley sizes as well. You just can't keep spinning the supercharger faster and make more power. It creates heat, which reduces density.

Hope that helps!
Randy

 

Doesn't the 15% SC pulley + the 2% Crank pulley spin the SC as fast, and therefore create the same heat, as a 17% SC pulley. If so wouldn't a total of 15% be the best?? That is what you indicated on the FAQ on the WMS website. Doesn't the heat gain from a total of 17% cancel the boost from spinning the SC faster?

 

Randy which belt should we use for 15% SC and 2% crank?

 

Yea, I'm wondering the same thing. I thought that the 2% pulley just made the 15% spin at the speed of the 17%.

Plus regarding the shuddering caused by the crank pulley, different people have different tolerances. The person that experienced seemed to be okay with it. On the other hand, I am not willing to take the risk. To me, it just seems like you're asking something to happen when you're really just getting the same effect as a 17%. Obviously is 15%+2% is not equal to 17%, then it's a different story although the shuddering is still a counterbalance to the difference between the 15%/2% vs. 17%.

[EDIT] I just read the parallel thread going and I recall somebody talking about shuddering at low revs, but I don't know who. Is it SteveS? If it is, did you guys figure out what it was?

 

How much HP would a 19% pulley make to a car with LSD (Such as mine)

 

 

The ratio isn't direct - you are actually less than a 17% sc pulley would be with the 15/2. Also, remember that we are getting the gain of losing the parasitic drag of the crank pulley weight. The FAQ was written before I tested the crank pulleys. What it indicates is that a 16% or so gives the most power on the dyno from an efficiency standpoint.

Steve had a tensioner problem - OEM from the factory issue - but the shudder he refers to I never felt, and I am overly sensitive to those types of things. I'm not sure what he feels, but he's going to the stock pulley again, and we'll see if that will cause the same shudder.

I use the OEM Continental belt on the 15/2 combo.

Hope that helps!
Randy

 

Is your new recommendation the 15/2 combo?

 

Yep - that's what I've been doing for a while now. I certianly think the 15 alone is still a great first mod, and I would only add the cp down the road. I would do the intake and rear bar first, then consider a couple of ways to go from there, the cp being one of them.

Hope that helps!
Randy

 

Randy
If you were starting with a JCW pulley would your reccommendation be to use the 3% crank pulley for best low end torque for mostly street driving? I guess were only talking a 1/2% difference one way or the other. Thanks

 

I would still recommend the 2% on the JCW - I have done quite a few. The JCW is only marginally smaller than 15% on the SC.

Hope that helps!
Randy

 

Now what about a 16% and a +2% crank? do you see a need for injectors since thats getting close to being a 19%

 

Stock injectors are good for up to 250hp.

16+2 will give you some where like 17.5 not even a 18 so you will be fine in my opinion.