I am confused as to why anyone would use under drive pulleys with the harmonic issues of the 4.6. Especially when you consider the type of person that is most likely to use the UD pulleys will be turning some high RPMs. I don’t know about yall but I am not planning on getting rid of this car anytime soon if ever. Its makes more sense to me if you want to free up some power to use an electric water pump. With no cooling fan being driven by the accessory belt how much parasitic losses can you recover? Please state your opinion with some facts, thanks.

 

So you understand my confusion on this subject then. I don’t understand their popularity, am I missing something?

 

I am of the same thinking, I won't do pulleys for that reason and the fact that I live in such a hot environment I don't want to run the risk of cooling issues.

 

I was confues about the popularity based on price. I read people saying don't pay more then about $20 - $25 per HP gain.

But the pullies are ~$200. And I have heard of gains around 5 hp. That is nearly $40 per HP. Sounds expensive for such a small gain.

 

Underdrive pullies don't decrease the rotational mass, they decrease the physical size of the pulley if memory serves

 

MTAS,

That's the problem. The rotating moment of inertia is function of diameter and mass (and the diameter is the stronger input!). So even if the mass is the same, because they are smaller in diamter, it WILL decrease the MoI of the damper, which changes it's tuned frequency. To keep the MoI the same, they you have to GREATELY increase the mass of the damper and they are not doing this, so you do get a MoI decrease.

 

OK, that makes sense now So what you're saying is that the U/D crank pulley is actually lighter than the stock pulley? If so, not good!

 

Not exactly. If the U/D pulley is the same weight as the stock one, there is still a potential long-term problem, but it is actually worse if the new pulley is lighter than the stock one. I guess it boils down to what works for a 5.0 works for the 4.6, but might sacrifice durability.

 

Interesting comments guys - I hadn't heard of this before....but I did notice that when I installed the Steeda ud pullies - the crank pully was not all that much lighter than the stock crank pully - just smaller diameter.....and for the record - I put 52,000 miles on an 00GT 5speed with not bearing issues whatsoever.....

Another point with the ud pullies is that while they don't add a ton of hp - they do seem to allow the engine to rev faster - not scientific I know - but that's the best I can describe...

Anyone actually weight the stock vs ud crank pully?

 

Here is an excerpt from SHM's write up on their own underdrive pullies: "The harmonic balancer retains 92% of the original mass, which is critical to long term durability of the engine"

Anyone know how much mass the Steeda pullies retain?

Edit: BTW, I've been noticing price increases for the Steeda pullies from $189.95 to $249.95. NorthCoast's price jumped on Friday and PartShopper now shows $249.95. LMPerformance is still $189.95. SHM's own brand are $169.95 and report 8 rwhp gain...$21.24/hp.

 

Meziere WP346 electronic pump claims 11-rear wheel HP gain. So far I guess the best price has been about 334.00. Kind of expensive but I think it is worth it. Also comes with a 2-year warranty.

 

Don't mean to be sarcastic but the physics of the pulleys bieng mentioned are not necessarily in question. It IMO is more the durability or longevity of other engine parts in relationship to the modification bieng done. Therefore; a specific mod should be well researched prior to purchase and its effects on the engine are somewhat irrelevant for the long term if you plan on driving the H E double hockey stick out of it or racing it. It is more likely that something else will break or wear out from the way you treat your car, and don't lie to yourself, you will drive it hard if not always at least some of the time. Purchase parts that work, IMO the pulleys have contributed to several sub 13 second passes on street tires. I am a believer.

 

I am sure they help, I am not questioning that but so would a 250 HP shot of nitrous. What I want to know is why would you pick the UD pulleys over an electric water pump?

 

The water pump only helps you with the hp lost through the water pump pulley. Most of the hp that is set free by underdrive pulley systems is through the decreased workload of the smaller crank pulley. Sure the waterpump helps by bieng larger but you are gaining the ability of the engine to turn all of the drive accessories with less effort. This includes the alternator/power steering/air conditioner. Other kits in the past have made use of the larger alternator pulley to get more gains, it is unfortunate that so far noone has been able to produce a pulley for the alternator that has the integrated one way clutch like the stock one is. Theoretically you could benifit from having the electric water pump and the smaller crank pulley, it would be cool to see a dyno comparison on this issue. Whoever goes with the water pump please post a dyno result with this change only and eliminate all of our guessing! Good luck, I will be anxious to hear what happens with this mod.

 

How serious of an issue is this imbalance? I was planning on getting a set of pullies until I read this post. How long will the bearings last with pullies on? Does it depend on driving habits? Plus is this an inevitable event? Is everyone on this forum that has pullies on their car going to be replacing bearings in the future? I just want to know since I too will be keeping this car for a long time.

 

SHM has this to say about their UD pullies: "The harmonic balancer retains 92% of the original mass, which is critical to long term durability of the engine".

So, I inquired with Steeda regarding the mass of their harmonic balancer and received this response from Gus Irizarry this morning:
"The exact engineering specs for our pulleys are proprietary. We spend a lot of time and money on R&D with Ford to get the exact engineering specs for their factory dampeners. We not only worked with Ford’s 4.6L engine engineering dept directly through our Ford Technology transfer program but also with Robert Yates Racing (the engine builder for all the Rolex Daytona Prototype 4.6 stroker engines as well as the 05 Mustang Grand AM racers) to get the harmonics of our dampener where they need to be for the 4.6L engines.
We are still the only people on the Ford technology transfer program and the only people with access to the actual numbers for the OE dampener. This allowed us to design our dampener the way it needs to be."

I ordered Steeda UDPs yesterday from LMPerformance.

 

Now that is some good information thanks.