Dyno results Underdrive pulleys

[8850]

Marine One:

You brought up an excellent point. On my 00 Vic (4.6 2V V8), the headlights did dim at idle and got worse when I had more accessories on at the time (HVAC blower, Air Conditioning, stereo, and turn signals).

I'm never going to try underdrives again in any vehicle, but that is just me. :SNSign:

Doesn't hurt a thing for your lights to dim somewhat. As long as you have a good battery and don't sit idling too long it's not a problem. I had a three pulley set on my 88 Mustang for years and never ran the battery down. I did use a lower ac fan setting in heavy traffic. You just have to watch your gauge and use common sense when in heavy traffic.

For the extra 10 hp it may not be worth it for some. But for the true racer who doesn't want to be beat by a car lenth then they are definitely worth it. That's what they were worth on my 88, about .1 or a car lenth in the quarter mile. Might mention too save about 1/2 mpg with them as well.

On my 06 I don't notice any diming of the lights at night. My alternator needle never drops even with ac on high fan setting. I have the factory alternator pulley and idling at factory set speed.

 

[JTGrant]

do you have the steeda pullies?

 

[metroplex]

I went through 2 batteries with my Steeda underdrive pulleys.

 

[8850]

I have ASP pulleys. The people that manufacture them for most companies that use their own logo. http://www.aspracing.com/frame.htm

 

[red05bullitgt]

I went through 2 batteries with my Steeda underdrive pulleys.

The current S-197 3v is completely different from the previous SN-95 2v set up...If I'm not mistaken ? the 2v required 3 U/D pulleys consisting of crank, water pump and alternator..The 3v only requires 2.. water pump and crank which only reduce the water pump and A/C speed by 25%.. being the 3v still uses the stock alternator pulley, there shouldn't be any type of reduced charging issues at idle..

 

[8850]

The current S-197 3v is completely different from the previous SN-95 2v set up...If I'm not mistaken ? the 2v required 3 U/D pulleys consisting of crank, water pump and alternator..The 3v only requires 2.. water pump and crank which only reduce the water pump and A/C speed by 25% Therefore alternator speeds along with charging should remain unchanged..

Not correct. The crank pulley drives everything that the belt turns 25% slower including the alternator and power steering pulleys. With a larger water pump pulley additional underdrive is produced by the percent size change in addition to the 25% produced by the crank pulley.

 

[red05bullitgt]

Not correct. The crank pulley drives everything that the belt turns 25% slower including the alternator and power steering pulleys. With a larger water pump pulley additional underdrive is produced by the percent size change in addition to the 25% produced by the crank pulley.

How do you figure ? the U/D crank pulley is actually smaller than stock only the U/D water pulley is larger, so how is this slowing the alternator and power steering by 25% ? when the crank and water pulleys are just switching sizes with one another.. therefore everything should balance out otherwise wouldn't a different size serpentine belt be required ?

 

[mustangsquared]

its a ratio thing... the faster a big drive pulley turns the faster a smaller one does... by reducing the crank pulley in size for a full turn of the crank a smaller portion of the belt moves (draw a V on a piece of paper the measure straight across it near the center and then at the widest point.... that distance is how much belt would be moved for the same degree of pulley turn at the two different sizes) then by going with larger pullies up top they turn slightly faster then the stock ones would BUT you gain HP overall... on my 91 I had "power and amp" pulley's that came with an "overdrive" alt pulley... it was so small there was alomost no room for the socket... it kept the alt turning fast enough to prevent the battery from dieing at idle...

 

[8850]

How do you figure ? the U/D crank pulley is smaller than stock along with the U/D water pulley being larger than stock, so how is this slowing the alternator and power steering by 25% ? when the crank and water pulleys are just switching sizes with one another otherwise wouldn't a different size serpentine belt be required ?

With a smaller than stock crank pulley everything is being driven slower. Even the idler pulleys driven by the belt. If the crank pulley was larger than stock everything would turn faster. With the driven pulleys, water pump, alternator, etc., larger makes them turn slower. So with the larger water pump pulley the water pump is driven even slower. Think of it like your bicycle. Smaller sprocket in the front makes the rear go slow or you crank faster. Larger in the back does the same thing.

An alternator pulley is not offered because of the grooving in the ID/shaft of the pulley/alternator shaft making it somewhat expensive to manufacturer. Were it offered larger than stock then it would be slowed and we would be seeing the light dimming at idle.

 

[bigcat]

i have thought about this a few times...here is my thoughts on how the U/D works for the accessories.

the crank pulley is smaller, so it moves less of the belt for the same rotation. with less belt being moved, this takes more revolutions to move the same amount of belt as a stock crank pulley.

the water pump pulley is larger, so it takes more belt to move it one turn, this slows down the water pump.

 

[8850]

i have thought about this a few times...here is my thoughts on how the U/D works for the accessories.

the crank pulley is smaller, so it moves less of the belt for the same rotation. with less belt being moved, this takes more revolutions to move the same amount of belt as a stock crank pulley.

the water pump pulley is larger, so it takes more belt to move it one turn, this slows down the water pump.

You have the idea correct Bigcat!

 

[red05bullitgt]

Goes to show what I know lol so apparently I had it all backwards but here's what I still don't understand ? if the smaller crank pulley slows the belt speed down, then why slow the water pump speed even further by increasing the size of the water pump pulley

 

[bigcat]

free up even more power, the water pump is the biggest thief in the equation

 

[red05bullitgt]

So how much of a charging reduction is involved after the pulley's are installed ? have their been any alternator or battery related issues that I should be concerned about someone had mentioned earlier that he had gone through 2 batteries while using Steeda U/D pulleys but then again I don't know if he was referring to a SN-95 2v or S-197 3v..I don't quite understand how theres such a difference in how the U/D pulleys affect the charging/alternator systems between the SN-95 and S-197..

 

[mustangsquared]

On my 91 when I added the UD's I had changing issues (a lot had to do with the Black Magic elec fan) so I upgraded my alt to the SN95 model (130 amp compared to 85 amp)... that cured my problem. The only time you will have a charging issue is if the stock alt only put out enough power to make things work... if it has some reserve capacity (IE the car and accessories require 120 amps and the alt puts out 130 amps) then you are good.

 

[metroplex]

The underdrive pulleys slow down the alternator (even if you use the stock alt pulley, the crank pulley is now smaller in OD), so the drive ratio for the alternator decreases with underdrives.

For instance, if the stock alt drive ratio is 3:1 and the alternator produces 80A at 600RPM engine speed, the alternator must turn at 1800 RPM to produce a max of 80A (at idle). When you upgrade to underdrives, the ratio changes. Let's assume it goes to 1.95:1. Your engine must idle at 923 RPM in order to turn the alternator at the same speed when you had the factory pulleys. Since the alternators generally produce max output at around 2000 RPM engine speed, you may need to go as high as 3000 RPM just to get the peak output of the alternator using the underdrives.

BTW those ratio #s I gave were comparing the stock pulleys with the 96-01 Steeda GT/Cobra pulleys (4.6 2V V8). The only difference in the Steeda Cobra pulley kit (99-01 Cobra) is the alternator pulley is for a 4G alternator, and not the 6G alternator used on the GT.

 

[wotfr]

Also by making the water pump pulley larger you can keep the same size belt.

 

[red05bullitgt]

That's exactly what I'm concerned about meaning if I upgrade to U/D pulleys ? will the stock alternator still be able to put out enough amps to avoid charging problems or would I also need to upgrade to a higher rated alternator ? In fact I have no idea what the stock alt is rated, is it also 130 amps or higher..

 

[metroplex]

Make no mistake, anytime you run a smaller than stock crank pulley, you are slowing down the alternator (UNLESS you use an even smaller alternator pulley to match the change in ratio, which is unlikely since oyu will have the OE pulley or a larger U/D pulley). In order to compensate for this, the idle speed in neutral/gear can be raised to keep the same amount of alternator output at idle. That doesn't quite resolve the a/c compressor, power steering pump, or water pump speeds though, and you will need to rev higher to get the same amount of max alternator output (as I explained before).

A lot of people don't report/experience any problems but it is in my humble opinion to avoid underdrive pulleys. When you decide to get a blower, you will generally have to swap back to the OE-sized pulleys again.

 

[red05bullitgt]

Can anyone who's running the Steeda pulleys let me know if the stock alternator is still able to crank out enough amps in order to prevent any charging problems ? and is the stock alternator rated at 130 amps or higher ? Thanks for your input and support in advance...