Under-drive pulley installation test drive

[type-S EF awd]

Keep in mind, that the alternator loses efficiency the slower it spins and these pulleys are designed and marketed for those who will have the engine's rpms high.

Just $0.02

[NoD~]

Just about every car I've owned, I've put an underdrive pulley on. Only 1 of all of those made little difference for acceleration: My 89 2.5L turbovan. It made a difference, but wasn't much in comparison to, say, the 1.5L Scion xB. That one was a HUGE difference. My Neons (1st and 2nd gen) have all shown positive gains in performance. The RPMs climb noticeably faster, that's for sure.

As for MPG, in theory, it should help. Though, I don't know how much real-world gain there is. Probably depends on existing setup and driving style more than anything, but figuring that you will hit your destined speed soon, that's less time throwing fuel at acceleration. It's less rotational mass on an idling engine, which should make your IAC valve close just a touch more when at idle. All good things.

I have never seen any damage come from an UDP. Though, I have seen where a belt was too tight and perhaps some sand or something got in there... sheered off one of the groves complete! On a high-end brand, to boot! But that wasn't my vehicle and all of the ones I've used/installed have been bulletproof.

[D.O.G.]

Originally Posted by type-S EF awd

Keep in mind, that the alternator loses efficiency the slower it spins and these pulleys are designed and marketed for those who will have the engine's rpms high.

Just $0.02

OK, my story isn't about an under-drive pulley as such, but the effect was the same.

I changed from a 3 speed gearbox with a 1:1 top gear to a 4 speed with a 0.68:1 top gear. This dropped lots of RPMs for everything, including the alternator.

Out for a long drive one night (lights on), in the rain (demister and wipers on), all at 60kph PSL in top gear (about 1250 RPM), with some engine on coasting thrown in, I stopped briefly, then couldn't restart the car.
The battery voltage had dropped low enough that it wouldn't crank the engine.

My point is that an under-drive pulley may be useful in some situations, but low speed cruising (at night, in the rain) isn't one of them.

I probably could have used an over-drive pulley.

[redpoint5]

Dog brings up a good point about having sufficient charging capacity with an UDP. My lightweight under-drive pulley set spins everything slower by 20%. This means the amps my alternator can deliver at lower speeds is reduced.

Here are some voltage measurements taken by someone that had installed an UDP on a TSX:



And the weight savings:



Looking at this image got me to wondering if adding "moon" covers or just taping over the holes in the pulley could significantly reduce the drag caused by constantly chopping at the air? These items are constantly spinning, even when stopped.

[JRMichler]

When I am chugging along at 25 MPH in 5th gear with the headlights on, the voltage drops from 14.X to 13.X. Since this is a significant portion of my driving, I cannot use an underdrive pulley.

[Superfuelgero]

All the more reason to cut the electrical load. When done together, its a good way to balance mpg and performance.

[oil pan 4]

Originally Posted by JRMichler

When I am chugging along at 25 MPH in 5th gear with the headlights on, the voltage drops from 14.X to 13.X. Since this is a significant portion of my driving, I cannot use an underdrive pulley.

Have you tried switching over as many lights as possible to LEDs?
Switching to LEDs saves me 4 amps with the running lights on and 12 amps with running lights on and brake lights on. Also saves 4 amps with the turn signal.

Switching to LEDs saved me from having to switch to a larger alternator.
My problem was my battery would drain when driving the suburban during hot summer nights when I had head lights on, radiator cooling fans running and sitting at a stop.
It was bad enough to where I would turn the head lights off while stopped.

[JRMichler]

My truck draws 20 amps with ignition on, heater blower on low, and headlights on. If I changed all small bulbs to LED, that would drop to about 14 amps.

I fantasize about an alternator delete, a deep cell battery, and a solar panel on the topper with charge regulator. But I would need enough battery capacity to run 4 hours without recharging, and that much battery will not fit under the hood.

[serialk11r]

Originally Posted by oil pan 4

Have you tried switching over as many lights as possible to LEDs?
Switching to LEDs saves me 4 amps with the running lights on and 12 amps with running lights on and brake lights on. Also saves 4 amps with the turn signal.

I looked up LED replacements, and my god are they expensive...I'd do it for a new car but not a creaky old car, but new cars are already coming with mostly LEDs. The first area I'd go for is actually the alternator, pick up a square conductor Densor alternator (~10% higher efficiency), put in an active rectifier (another 10+% efficiency), and you'd have lower drag on the engine as well as more amps available. While you're at it you can add a motor controller, tap the windings, add a battery pack, and get a mild hybrid drive.

[Goldenstate]

The thought of a high efficiency lower RPM alternator with and active rectifier is an interesting ecomodding thought. Where can one find out more on this type of improved square conductor alternator?

This style of alternator seems to be something new on the market and sounds like it might be something of interest to our needs. Perhaps it is one of the many advances in technology one can find in foreign countries but still not for sale in the US.

I did run a #4 ground cable from my alternator to negative ground terminal of the battery. It was amazing how the Scanguage voltage readout stabilized to with in +/_ a tenth of a volt most of the time. I had never seen the voltage that stable until the ground cable was installed.