Under-drive pulley installation test drive

[Goldenstate]

Installed a set of CNC machined under-drive pulleys on the 1999 F150 4.6 engine yesterday. I immediately noticed a decrease in noise from the engine area as everything was spinning slower. The first driving experience was interesting as I quickly realized I had more power not being lost to the serpentine belt. Most of the reports I have read say one can feel the difference in power with the under-drive installation.

I did a short road test this evening and was disappointed to only achieve 22.95 MPG. Last fall before we went to the winter fuel mixture, I had test runs that achieved 25.5 MPG. I was hoping for at least breaking the 26 MPG barrier but that may have to wait until the Summer blend fuel is once again part of our life here in CA.

My other thought is to fill the tank with some Chevron Supreme and see if the higher octane fuel will improve my results. A Scangauge has been ordered and it may well give me some more credible results.

[2000swift]

What percent underdrive pulley was it? 25% 50% ect...

[redpoint5]

Is your pulley set aluminium? This should lower rotational mass and improve acceleration. I have no idea how much the reduced weight can improve acceleration. It would be neat to see some dyno or 1/4mi runs to quantify this.

It's unlikely you will observe a measurable MPG increase that you can confidently attribute to the pulley set. My best guess based on the research I've done online is that you might get 1% better fuel economy. This is within the margin of error for any test you would do to quantify the savings.

I'm happy to hear your butt dyno is noticing the improvement. I installed an expensive aluminum underdrive pulley set on my TSX, but did not notice any difference. Perhaps I didn't have enough time in the car in stock form to calibrate my butt dyno before I installed the kit.

[Cobb]

Id love a set for my insight and sidekick. Your truck maybe geared property to begin with for your accessory drive.

[Goldenstate]

Redpoint5,

The pulley set is machined from some high grade aluminum yet retains the old harmonic balancer. It appears to be about 25% smaller in diameter than the stock crank pulley.

It is made by BBK and on YouTube there is a short video showing the installation of a similar set of parts on a Mustang. At the end they do a dyno test to show the increase in power across the RPM band. Their results do not match the claims of 10-15 horsepower but are more like 3-8 horsepower. Even at that level, one can feel the difference. It is the most impressive increase in power I have noticed to date with all the different things I have done to make things more fuel efficient.

I will be doing a 90 mile road test tomorrow on a regular route I have done other road tests on recently. That will be a better evaluation than the short test I just completed yesterday.

[Goldenstate]

Over the past few days I traveled 67 miles around town and made a 100 mile road trip. The combined 167 mileage gave me 25.21 MPG which is very encouraging. Perhaps the under-drive pulleys are worth the trouble after all. The short road trip probably was not the best way to test a change.

Of interest was with the much more quiet under-hood noises, I was able to diagnose a bad idler pulley bearing. It was replaced during the 167 mile stretch of time but I doubt it was a significant influence on the mileage. I suspect the tensioner arm pulley bearing is in bad shape as well. Will be replacing it in the next few days.

The Scanguage arrived yesterday and was installed today. Things should get more interesting real soon.

[campisi]

I put a crank underdrive pulley on my old 99 Dodge Ram and noticed ZERO improvement in either driveabilty or MPG. There probably was some improvement but not that I could document. I just don't think it's worth it especially on a truck so I took it off and sold it. An underdrive pulley system reduces cooling capability and your power steering boost at low speeds. If you ever tow anything with your truck this would NOT be a mod I'd advise. I think those pulley sets are more aimed at cars, especially guys who track them (and have AC deletes and other track specific mods).

[SlideWRX]

I put an underdrive pulley on my Mustang (also 4.6l, but a 3 valve) and got 0.5 mpg, give or take. Noticed the available power change, but nothing big.

[Goldenstate]

With a few tanks of fuel through the truck with the underdrive pulleys installed, I have noticed 1-2 miles per gallon improvement in mileage. Nothing is real big in mileage improvement with a full size truck. It has been one of the best improvements to date. Engine coolant temps are normal and the power steering feels just the same as before. The alternator is running 14.1 to 14.7 volts all of the time. Will be running a ground directly from alternator to the negative battery terminal in the next few weeks.


Next up is new tires from Bridgestone with their new LRR rubber blend. More of a SUV tire instead of a light truck tire. I seldom haul anything and never tow since the sale of the family ranch.

[Mista Bone]

On my CRX I noticed about 5% gain when switching to Bridgestone Ecopia EP100's at normal inflation pressures, then another 5% gain after pumping them up a bit.

1) 44 mpg, Old rims and tires @ 35 psi
2) 46.5 mpg, Miata LW rims and LRR @ 35 psi
3) LRR @ 48/45 psi, 51 psi cold sidewall rating for the tires.

With step 3 on any vehicle, handling my become a huge safety issue.