Has anyone attempted to put underdrive pullies on the I-6 yet? I've looked hard, but cant find them no where. Any help would be appreciated.

 

I really don't think they would be worth the money since the 300 is such a low revving engine. I've taken the belt completely off my truck at the track and only gained a tenth of a second. If you only gain a tenth with nothing turning at all, how much could you possibly gain by just turning things slower? FWIW, a tenth of a second on a 17 second truck is about 3hp.

 

[updated:LAST EDITED ON 29-Oct-02 AT 09:08 PM (EST)]>I really don't think they would be worth the money since the
>300 is such a low revving engine. I've taken the belt
>completely off my truck at the track and only gained a tenth
>of a second. If you only gain a tenth with nothing turning
>at all, how much could you possibly gain by just turning
>things slower? FWIW, a tenth of a second on a 17 second
>truck is about 3hp.

Did you try removing the fan too? I bet having no fan would free up another 3hp. BTW, when you removed the belt, wasn't your steering then no longer powered? How did it feel?

 

if you remove the belt, then isn't the fan no longer turning??? how could you gain more hp???

 

There was some testing done at some point by Car Craft or Hot Rod. I don't remember which. They showed how not driving the alternator cost a decent amount of power. Modern ignition systems need the extra volts to push that spark. Also showed how a GM style alternator only consumed about .12 horspower on a full power blast. They did that by running one of those high volt racing batteries so they could test the difference between with alt. drag and without, while maintaining voltage to the ignition system so that wouldn't be a factor. If you're interested in trying things see if you can re-rig your truck to run only the alternator and see how that works. Or you could unhook the alternator and install a 14-16 volt racing battery, and see how it works out.

Think they also did dyno pulls showing a loss of almost 50 horse on a 4 blade fixed blade fan. The clutch type sucked up something like 27 horse.

I wouldn't take those numbers as gospel. It's been a long day, and I read those figures at least 10 months ago.

 

The steering didn't feel too bad, but when I turned the wheel it spit out some fluid. That is a normal thing for a Ford. The biggest issue was that the engine got hot before I got back to the pits. It didn't get badly overheated, but I won't be trying it again.

I don't think not spinning the alternator hurts these trucks that much. I remember the article sited above and it was based on a full race vehicle with an electic racing fuel pump, cooling fans, high power ignition, etc. The vehicle used in the article uses up power 10 times faster than a typical F-150. A few years back I had an alternator failure in my truck about 10 miles north of Ft. Worth. I drove the 4+ hours back home and the truck still ran just fine when I got there. The stock fuel pump and engine control stuff doesn't pull that much juice, it's all the extras that tax the electrical system.

 

This article was done on the dyno. It showed a direct relation between voltage available for the coil and power. Maybe one of the wiring gurus can chime in and clarify. But still think you'll make more power with the alternator turning.

 

I know someone with a 94' 4.9L with underdrive pulley's he got them from summit

 

i know when i have my stereo my gas milage suffers due to the extra voltage and then it needs to produce more for the other accesories and ignition, etc. this has a relation to HP cuz it needs more to turn it. but underdrive pullies on anything BUT a 4.9 seem meaningless.

 

 

Most alternators put out about 14V and 100 amps at peak. That equals 1400W at peak output. 1hp=746W. 1400W=1.88hp If you assume the alternator is 50% efficient it still only consumes 3.8hp. It is very rare that an alternator would ever be running at that level. Even with the lights, AC, radio, etc. on the output is typically less than 50A, which gets us back to 1.88hp to spin it. Assuming the torque required to spin the alternator remains constant regardless of rpm, which is probably a reasonable assumption as far as generating electricity is concerned, the power saved will be proportional to how much it is underdriven. If you underdrive it 30% you save a whopping .56hp. If I had $100-150 to spend I could find a better place to spend it than underdrive pulleys.

 

[updated:LAST EDITED ON 01-Nov-02 AT 09:36 AM (EST)]The underdrive pullies also slow down the water, smog and power steering pumps and the A/C compressor. I suspect there's a lot more HP saved there than in the alternator. As to ther low revs of the 4.9 being a factor, that might or might not be true. If Ford runs the accesories on the 4.9 at a faster speed to make up for the lower working RPM, then underdrive pullies might have the same gains as on a 302.

I've always condidered the biggest gain from underdrives to be bringing the accesory RPMs and HP losses back into the stock range after fitting bigger gears. The gains are minor either way. Somewhere I've seen dyno numbers on the order of 5 HP, nothing to write home about.

 

$100-$150 for 5hp isn't that bad of a deal. Most here would consider a K&N FIPK for what, $100-$130? How much does that gain? Who here has added an ignition in the $200 range (6a + coil) and how much hp gain is there? It may be a bit more labor, but the price/performance is up there with other common boltons.


-=Whittey=-

 

[updated:LAST EDITED ON 03-Nov-02 AT 11:47 PM (EST)]I've posted this on another BBS, so this is just a cut&paste:

In my somewhat informed opinion, this installation is counterproductive labor. Consider:
1. The alternator is controlled by the voltage regulator, which will cause the alt. to draw as much power as it needs from the engine, regardless of the speed at which it is rotating. This means that, with a smaller pulley, the belt will be put under higher tension (because of the shorter lever of the small pulley) and will be forced around a smaller radius curve. Both of these situations will cause the belt life to be significantly shorter, and the tension is applied directly to the alt. & crankshaft bearings, shortening their lives.

2. The power steering pump pumps fluid as demanded by the steering box. Assuming you will still want as much assistance in steering as with the larger pulley, at low engine speed you will cause the same problems as with the alt.: higher tension, smaller radius, shorter belt and pump lives.

3. The air pump is unregulated (and a VERY small drain on engine power), but underdriving it will still have some effects, to wit: at low engine speed, there may not be enough air flow available to the air injection system and catalytic converters to meet the goals the EEC was programmed for, resulting in high emissions/failed smog test/"Tread Heavily".

4. The difference in pulley sizes will probably change the total length of the belt(s), meaning you will not be able to walk into a parts or tune-up store and get the right belt(s) the first try. And when you get the new belt, it won't be the same one 5,000,000 other trucks are using, so it will cost more.

5. The only system that will probably be affected the way you intend is the A/C compressor, which will not be able to produce the pressure needed for the cooling system at low engine speed, which is when I assume you really want the power to be scavenged for propulsion. But you will STILL see the effects of tension and belt flex and WHY WASTE THE EFFORT??? Just turn the A/C off when you don't want the power to be drained.

I've spoken to engineers and other mechanics, and the opinion I've formed is that the underdrive pulley is a HOAX! I have never seen empirical evidence that the effect is appreciable on the trail, where you are paying for it to be. I think that anecdotal evidence ("I put them on and my rig works 1000% better now!"), while useful for some mods (like shocks, electric fans, tires, gears, etc.), is at best, questionable. Who knows what other mods were done during such an involved procedure?

 

i went to the electric fan and gained 10 hp and 2 mpg and on top of that my 94 f 150 runs so much better without the belt driven fan i and upgrading to underdrive power steering and alt you are giving bad advice the underdrives and electric fan setup on a late mod f150 work big time