Underdrive Pulley Question

[HannahWCU]

I have been doing alot of research on this modification. Some say it will increase mileage some say it wont. All say it will not pay for itself. But my question is this: I am having the timing belt replaced in my neon and the mechanic that is doing the work said he would install the underdrive pulley for free (if I bought it) since he has to pull the stock pulley to replace the timing belt. The pulley I am buying comes with replacement belts too.

My commute is 50miles each way (25,000miles/year), so even a small (1 MPG, 2.5%) fuel economy increase would be beneficial.

So, since the installation is free, and belts need to be replaced anyway, would you install the $130 underdrive pulley?

[Daox]

I agree with the general consensus. It will improve mileage an imperceivable amount, and it will never pay for itself.

[t vago]

I am going to install one on my truck soon. At that point, I will use the ScanGauge to determine if there's a noticeable increase in FE.

[oil pan 4]

You could just about break even.
Since you drive a lot of highway miles you are better tailoring the engine set up your use.
If you did all city driving you would want to leave the stock size pully on.

My metric on weather or not I do a MPG mod is $250 (absolute max) per MPG.
I like to spend $200 or a lot less if possible when picking up an MPG.
I will also spend $20 per horse power (as long as it doesn't effect low end torque or fuel economy). Or up to $20 to pick up each ft.lb of torque on the low to mid range only.
I like to spend a lot less if possible on these too.

So $130 for a possible 1MPG, yeah I would do it given the low price and unproven pay off. I think driving tons of highway miles you have a better chance of pay off.

[HannahWCU]

I am leaning towards ordering it. I have not really seen any quantitative results, unless someone on here has installed one, but I couldn't find it searching.

If I get it, we will see if there are any improvements. My commute is pretty consistent and so is my mileage (check my fuel log graph). Anything from 2% (1mpg) or greater should be pretty easy to see. Might even be able to see a 1%.

Originally Posted by oil pan 4

So $130 for a possible 1MPG, yeah I would do it given the low price and unproven pay off. I think driving tons of highway miles you have a better chance of pay off.

That is exactly what I was thinking. @$3.50/gallon a 1 MPG improvement would give me a payoff in 30 months. But the REAL savings is the reduction in greenhouse gasses, a little bit here and a little bit there.

Seriously though, its not ALWAYS about the money is it?

[HannahWCU]

Well, I ordered one. We will see the results once I get it installed.

[Ryland]

Belts are more efficient when they are going over larger, not smaller pulleys, under drive pulleys were made popular in racing, where the engine is running close to red line.
My understanding is that a slower turning alternator is going to be putting out less power so it is more or less going to be maxed out more of the time, so I would like to know if people who have under drive pulleys need to replace their alternator more often, because that would be an issue I would keep an eye on.

[HannahWCU]

Yes, I realize from my research that there should be almost no savings from the Alternator, but I have got to think that there will be some savings from the Power Steering. At highway speeds (which is 95%+ of my daily commute) the power steering isn't doing much work at all. But there are still parasitic losses that will be reduced from under driving. To what extent no one seems to know.

I haven't seen any ABA tests for underdrive pulleys, nor have I seen anyone on this forum who has tried one. So it looks like savings estimates are just an educated guess. If there ends up being no savings, then I am out about $120.

[SentraSE-R]

Keep us informed of your results. I doubt you'll see any improvement in fuel economy, but appreciate your efforts to find the answer for the rest of us.

[99LeCouch]

The UDP might be lighter, so it's easier to spin. Way back when, I installed a lightened stock-size pulley on my old Hyundai. Custom-made piece. The engine did rev easier, and my gas mileage went up a little bit on highway trips on flat land.