Underdrive Pulley?

[mwalters]

Has anyone tried one of these yet??
http://www.ecstuning.com/Volkswagen-Jetta_VI-Sedan-TDI/By_Brand/N-P/Neuspeed/ES2826026/
Just curious if 1) the HP increase claim is accurate, and 2) if the A/C and alternator are still turning fast enough for efficiency.

 

[993er]

Anything to make a buck. Simply incredible.

Simply put, it is more bling.

 

[azthegame]

I have one, revs a lot quicker, no noticeable difference in fuel economy or air conditioning performance. With such a minimal gain in power it's really hard to tell if you truly get anything power wise from it..

I only recommend it for reasons of 1) it looks nice compared to the stock one, it's way lighter so you know it surely has less strain to turn it. 2) you have money burning a hole in your pocket and must spend it on something.

 

[nord]

1. The difference in mass between components is of no measurable consequence.

2. Accessories soak up power. A higher gear ratio basically means that your engine turns a bit more than stock for every revolution of the accessories. While the ratio makes for somewhat easier turning of these components it doesn't reduce the power they absorb.

3. Reduced rotation often reduces the capacity of the accessories being driven. This is especially true under adverse conditions.

Our cars use a variable displacement valve on the a/c unit which self adjusts for the conditions under which it operates. In effect you've switched gears and slowed its input. It reacts by merely upping the flow of coolant. The alternator is much the same as it sheds or increases its load depending on the level of charge and the load being placed. In other words with a fully charged battery and light load the alternator will be virtually in a freewheel mode. Spinning it slower will merely make it less efficient and take longer to get to a fully charged state.

About the only constant possible savings is your water pump. Spin it slower and you pump less water. As long as you circulate enough water to keep temps in specs you save a bit of energy. That is, of course, if you aren't too concerned about keeping the cabin as comfortable as possible.

It's best to remember that everything is a compromise. What you get in one place you'll give in another. There's just no free lunch to be had.

 

[mwalters]

Isn't the water pump run by the cam belt though??

 

[nord]

Absolutely! My point being that the water pump is one of those things where a slight savings can be realized. Not really an alternative in our cars but one used where applicable. Usually an electric drive motor. The real savings on a conventional system is the elimination of the engine-driven cooling fan. The pump is very minor.

On our cars a smaller drive pulley on the serpentine belt will slow down the input to the accessories. For all practical purposes there can't be a net gain though a slight increase in available performance may occur for a short time. Eventually the normal operating needs of the car will catch up.

 

[macoombi]

I know from my previous experience with Taurus SHOs that underdrive pulleys were a popular modification but that's a completely different ball game. Some guys installed them (or a single crank pulley) to protect the accessories from high rpm wear and tear. But that's on an engine capable of 8000+ rpms.

If you're trying to knock a tenth of your quarter mile time, they're maybe worth buying. If you're looking to gain MPG, forget about them.

 

[compu_85]

I'd rather keep the alternator spinning faster so it doesn't have to work as hard...

-J

 

[Ol'Rattler]

Really stupid mod. you could try running with the serpentine belt removed or just send the $188 to me...............

 

[DjEclipse]

If you're trying to knock a tenth of your quarter mile time, they're maybe worth buying. If you're looking to gain MPG, forget about them.

Or go on a diet, cheaper and more practical.

 

[993er]

Or go on a diet, cheaper and more practical.

And healthier.

I have to chuckle at shoppers that zig-zag down the parking lot aisles trying to get the closest parking spot to the store door.

I am in the store already after walking from the far side of the parking lot and they are still looking for a spot. LOL

 

[azthegame]

And healthier.

I have to chuckle at shoppers that zig-zag down the parking lot aisles trying to get the closest parking spot to the store door.

I am in the store already after walking from the far side of the parking lot and they are still looking for a spot. LOL

I hate that too, it's so dumb.. You are about to walk into the store or mall and walk a bunch, what's an extra little bit in parking lot? People do it at the gym too!! You are there to work out, walk a little!! Lol

 

[DjEclipse]

I hate that too, it's so dumb.. You are about to walk into the store or mall and walk a bunch, what's an extra little bit in parking lot? People do it at the gym too!! You are there to work out, walk a little!! Lol

Welcome to North America, where everyone is entitled, impatient and extremely lazy, even when on their way to doing physical activity.

I usually have a look, if the isles look full I will park far away and walk. Now I always park far away and walk as I only owned my car for under a week and some ******* opened his/ her door into the side of my car and put a dent in it!

 

[redbarron55]

If the alternator turns slower then the voltage regulator will increase the field current to meet the setpoint, increasing the power demand on the alternator to what it would have been if it were turning faster.
That is until the field saturated and the Alternator cant put out enough current to meet demand at that RPM.
All in all pretty much a waste of time in my opinion for a car driven on the street.