good or bad idea underdrive pulleys

[bbbbssss]

Are underdrive pulleys a good idea for my s10 blazer stock 4.3v6 ?? Sounds easy to install, but I'm wondering if I'm really gonna feel the increase of horsepower??

[ZR1-S10]

Your feel a little gain(engine seams to rev faster) with some loss of amps. And yes there easy to install.

[stepside2k1s10]

personally, I wouldn't go there (I'm not real experienced in installing pulleys) but I suppose it depends on how much smaller the pulleys are going to be (you're going to want to make sure they aren't too small) but if you can do it, go for it!

[nomaboy]

i got about 1-2 tenths in the 1/4. but i did my underdrive pullys and e-fan at the same time so that gain is with the two combined. they will affect cooling ability and alternator output. if you run a low temp thermostat the cooling won't be an issue. if you don't have a stereo system then the alternator output won't be a ploblem. if you do have a system you will need a high output alternator and a optima battery.

[ZR1-S10]

ASP's pulleys are 25% underdrive and shouldn't cause much problums with an otherwise stock setup. If you have a big stereo system and/or cooling demands then just install the crank pulley.

[Sparky2263]

I can't believe I still don't have underdrives on mine. Oh well, one day.......

[LEADFOOT]

Don't buy Jet underdrive pulleys. Buy the March set. I bought Jet and the alt. pulley is bigger than the stock one, so it slows the alt down alot. It slows it down so much that it won't even charge at idle. Volt meter sits at 12 volts. The people at Jet don't know what they are talking about either. They told me I couldn't use a smaller pulley. I called March they sold me a 1 7/8" alt. pulley which brings the alt. rpm pretty damn close to the stock rpm. Call March first and ask if their set comes with a 1 7/8" alt. pulley, I think they said their set does. Jet buys their pulleys from March. When I installed mine I had to grind a little off the stock crank bolts to get them to fit with the new pulley. And had to use an open end wrench, can't get a socket on them. I gained .2 sec in the 1/8 and same for the 1/4. I already had the efan installed when I put the pulleys on so the .2 sec is the gain I got from the pulleys. If you have the clutch fan still on you might see a slightly higher gain. Keep in mind that everything the crank is turning will turn slower with the underdrive pulleys.

[Sparky2263]

I'd like to purchase just the crank pulley. Does anyone sell it like that?

[LEADFOOT]

I'd like to purchase just the crank pulley. Does anyone sell it like that?
I'm not sure if they do. Check with March. Here is their site http://www.marchperf.com/index.html you may want to go ahead and get the 1 7/8" alt pulley. The picture of the set shows the big ass alt. pulley so I'm not sure which alt. pulley it comes with. If you can buy them seperate then get both. I'm pretty sure you can get them at our store.

[JROD©™®]

me 2 sparky...simple cheap and yet have not done it. the store sells them...only thing is we'd have to pay for the alt pully...unless we went elsewhere and found it the crank pulley seperate...

[Sparky2263]

$73 at our store. Anybody ever buy from our store? Is there shipping and "handling"?

[bbbbssss]

So a Crank pulley and a 1 7/8" alt pulley is all im going to need.
Whats the differeance between the March Power & Amp series VS the Performance series?? One is for hauling and stop and go driving the other is for nomal driving.. Are the pulley sizes different???


Thanks for all the replies...

[kuhndog56]

Get the power and amp series, its the one wiht the smaller diameter alt pulley and wont draw alot of amps.

[03 Rado]

Summit sells just ASP crank pullies alone and I think the total with handling in around $72. Not that you will gain anything by using them after all the alt and powersteering still will eat the same power as before when get asked for load and the waterpump which gives you a whooping 10 h.p, if you got to electric, which shows you its load will be only 25% of that AT BEST. 2.5 h.p. and I'll give in and give you .5 h.p. for turning idlers slower!

[03 Rado]

So a Crank pulley and a 1 7/8" alt pulley is all im going to need.
Whats the differeance between the March Power & Amp series VS the Performance series?? One is for hauling and stop and go driving the other is for nomal driving.. Are the pulley sizes different???


Thanks for all the replies...

The alt needs 750 rpms min. with the factory pulley in place to make full load capabilites. The power set underdrives by 25% more to allow SO-CALLED extra power and its larger in diameter so it needs over 1250 rpms to get the same charge as 750rpms with the factory one. Amp series uses a smaller 25% overdriven pulley to maintain it close to factory charge rates, but falls about 75rpm different. You will be sorry if you choose the Power set, you WILL experience charge problems at idle!

[Sparky2263]

Summit sells just ASP crank pullies alone and I think the total with handling in around $72. Not that you will gain anything by using them after all the alt and powersteering still will eat the same power as before when get asked for load and the waterpump which gives you a whooping 10 h.p, if you got to electric, which shows you its load will be only 25% of that AT BEST. 2.5 h.p. and I'll give in and give you .5 h.p. for turning idlers slower!

Bad info there Rado. EVERYBODY who has dyno tested pulleys have found between 5-15 horsepower. The crank does the most for you by slowing everything else down.

Having to accelerate everything at a slower rate is the key. The vehicle accelerates faster because there is less acceleration load on the crank pulley.

[nomaboy]

Don't buy Jet underdrive pulleys. Buy the March set. I bought Jet and the alt. pulley is bigger than the stock one, so it slows the alt down alot. It slows it down so much that it won't even charge at idle. Volt meter sits at 12 volts..
that is why i don't use the alt. pully on my truck. cause i bought the jet pullies and other than the bigger alt. pully they are all right.

[03 Rado]

Bad info there Rado. EVERYBODY who has dyno tested pulleys have found between 5-15 horsepower. The crank does the most for you by slowing everything else down.

Having to accelerate everything at a slower rate is the key. The vehicle accelerates faster because there is less acceleration load on the crank pulley.

Not bad information, just finished the part they arent paid to write up when they test them, or bother to look at. Do they turn the power steering during a dyno run, NOPE. Do they turn on the extra juice needed for a amp,stereo, headlights etc, NOPE. Dyno it with those off or not loading fully applied and you might see 5-7 h.p. How much juice do you need to run the basics, isnt that the job of the voltage regulator and now today the ECM for demand loads. You might pull 20 amps tops maybe, but turn those lights on, the heater and crank the stereo and youve asked for the full 80 amps the system is capable of most times and that takes h.p. when it kicks in, just watch your tach when your turn those on at idle, tell me it doesnt load pretty hard. Same goes for the power steering, lower rpms make is less functional, but still eats power on demand. AC doesnt make full charge at times and can run with a warmer output temperature, but its still gonna try to eat the 20 h.p. it takes to run one. Some things it eases the load an or you dont need the rpm, others will eat the same exact power required to do there jobs.
Just think about the knowns in advertising first, always advertise or have mags feature the worst available vehicle in its subscription style. Then think about draws of certian features, they dont care what rpm there at, they eat the same power!

[nomaboy]

the idea of underdrive pullies is the same concept of gearing your truck down.you make it easier for the engine to power the wheels when going from 3.42 to 3.73 rear gear thus increasing acceleration. underdrive pullies do the same thing they make it easier for the engine to increase RPM's.
that is why people hear report to gaining .2 in the 1/4 by using them.

[ZR1-S10]

Yeah dispite any aruguments people may have when it comes right down to it your WILL feel and see an inprovment with next to no problums (the powerstreering feels the same and so does the a/c only a slight loss in amps). In the end it's worth it.

[03 Rado]

I know the premise of them, just actually did the math part to explain why when I did them years back I lost 1 MPG running them. Clutch fan was under load longer and if it was .2 tenths REAL life and not combined with some other mod that would equate to easily a 20 h.p. gain! If you were running a normal fan I could see some real gains, but it takes X horsepower to make 80 AMPs of electricity, thats is fact and science. It also by the same science is going to use X horsepower to power a power steering pump. Idlers do eat power to turn, but this one is truely NEGLIGIBLE. Water pump is really he only gain to be had since its moving less volume of coolant which the impellers fight against.

[nomaboy]

it takes x amount of torque to get a 4000 pound truck off the line. when you gear it down it gets the truck moving faster. it takes x horspower to spin the power steering pump. when you put UD pullies on it it makes it easier for the engine to spin the pump. i got about .2 in the 1/4 when combined with the e-fan. my truck always has been stubborn. but leadfoot noticed a .2 with just the pullies. if they didn't work to make power then nobody would notice the difference. i am not saying your theory is wrong. actually i see your point, but you can't argue with the timeslip.

[ZR1-S10]

Man you two like to aruge! Still, if you want a simple yes/no answer, then yes go with them.

[03 Rado]

i got about .2 in the 1/4 when combined with the e-fan. my truck always has been stubborn. but leadfoot noticed a .2 with just the pullies. if they didn't work to make power then nobody would notice the difference. i am not saying your theory is wrong. actually i see your point, but you can't argue with the timeslip.

First line says most of it for anyone looking, COMBINED with Efan. Oh you can dam well feel it rev easier with a efan, but do pullies alone and feel nothing.
I can and will argue with a timeslip, only because it wasnt run right before and after the mod on the same track, same day etc. I can run one day dam near .5 difference from the next day with the same mods in place. Track condition, track temp, outside humidity etc will all change a time slip on their own.

When someone independantly, no magazines, preferably me watching, but at least someone very trustworthy takes a vehicle fully warmed up with everything running, dynoes it, quickly changes the pullies and adds the new belt and runs with everything on again and finds over 5 h.p. by doing it, I"LL EAT ****!!!

[Rhansen]

This thread is funny.
IMHO pullies are only good for dressup.

[Sparky2263]

it takes X horsepower to make 80 AMPs of electricity, thats is fact and science. It also by the same science is going to use X horsepower to power a power steering pump. Idlers do eat power to turn, but this one is truely NEGLIGIBLE. Water pump is really he only gain to be had since its moving less volume of coolant which the impellers fight against.

You're using theory to explain it away but it's the wrong theorys.

1) The alternator drag is mostly caused by having to spin the armature, not the X amount of horsepower required to make X amount of amps theory.

2) The power steering pump, in straight line acceleration, uses negligible amonts of hp.

3) The higher the rpm's the greater the gains.

You're not going to sit here and try and convince people that turning an A/C pulley, a water pump and an alternator at 30% less speed isn't going to increase their rate of acceleration are you?

Find a theory for rate of acceleration and plug it in. 3 times. 1st gear, 2nd gear and 3rd gear. Have to accelerate in each gear in a straight line contest.

Me? My theory's lie on the race track and my trophy room.

[Sparky2263]

One other thing, all this talk about the alternator not charging at idle. So? Newer cars are turning the field off at idle for this very reason. Alternator's (as compared to generators) just aren't very efficient at idle. So the computers are turning them off at idle to save fuel. With smaller batteries than most of us use.

Most people put on underdrive pulleys to lower their ET. Period. They accomplish this for a minimal outlay compared to other mods accomplishing the same feat.

I'll repeat myself, RATE OF ACCELERATION. Get it?

[03 Rado]

Lets start with number 1.

1) The alternator drag is mostly caused by having to spin the armature, not the X amount of horsepower required to make X amount of amps theory.

Ah so I'll have to guess it doesnt take horsepower to make electricity, cause thats what your implying. Turning the armature in itself is just like turning a idler pulley, negligible. When you turn the fields on it when it eats its power since has become more a less a giant magnet refusing to be spun in sorts, this requires power to overcome and the more power asked for the more its going to drag. So it is 100% X amount of horsepower to create X amount of amps, aruging that is stupidity in the least.

2) The power steering pump, in straight line acceleration, uses negligible amonts of hp.

OK so why then underdrive this accessory since its negligible, your stating this. What gain is there to be had, along with now the idlers nothing. Alt we allready now is nothing to gain ,so this leaves the water pump

3) The higher the rpm's the greater the gains.
How is it going to create a higher RPM at best you hope to reach the max rpm faster!

You're not going to sit here and try and convince people that turning an A/C pulley, a water pump and an alternator at 30% less speed isn't going to increase their rate of acceleration are you?

Yes I am, because I wasnt born just yesterday. AC units under power and alts are all going to create the same drag with or without pullies. There is nothing to gain by spinning them slower. Engaging the clutch and creating pressure with the AC is going to use 20 h.p. no matter how fast it turns. Where in RPM it may make full MAX air is another story. Alts the same thing , but you'll never understand that if something is going to take power to make power, it doesnt change the parasetic drag needed to be applied to produce such.

And then again how many here strictly race? Use their truck for nothing other than. Again you might see 5-7 h.p. if your lucky if nothing else comes into play like a straight line race, but on the street, nil. As Rhansen said it then becomes and issue of pretty!!

[03 Rado]

Some tidbits from a racing site since YOUR MR TRACK>

What many people fail to comprehend with the alternator is that if you
slow it down, the voltage regulator will simply crank up the field excitation
to whatever value it takes to maintain voltage. The mechanical effect
is the torque requirement rises as the speed decreases IAW
torque*RPM/5252 = hp. Since watts are the same as hp, the alternator will
draw a constant hp to supply a given watt load. The only difference
will be the very minor air drag difference.

Before you disconnect the alternator, consider my discovery the other night.
We had a small block Chevy on the dyno with an MSD. To supply power we
always use a fully charged battery, and leave the charger running to
produce 13.8 volts. Well, the other night we forgot to turn on the charger,
and the engine was down about 17 horsepower. The charger went back on
and the power came back. We then began to experiment. Anything less than
13.4 caused a significant power loss, more than 14.0 did not help. Now,
these were not the most efficient combustion chambers because the racing
class required mostly stock parts, so they were very sensitive to MSD
ignition. More efficient chambers are less sensitive to the MSD, but
it is still more than 2 HP.

You should check out the number of race cars, in all classes, that run
alternators. You will be quite surprised how many use them. When we
are looking for that extra 0.01 second, we make sure the alternator is
working.

Ignition systems are power hogs and sensitve to voltage, especially the MSD.

>On the flow bench thread it was mentioned that you could check to see how
>inflated the underdrive pulley merchant's claims really are with some
>torque sensors. Well, I've also seen more realistic claims of 5HP ... however, I think it's Duttweiller who says he
>sees no difference on the dyno. Again, I don't know as that really
>proves anything, since I would think it would be very difficult to
>measure small HP gains on the dyno reliably. Bottom line, IMHO? Good
>hype and hoopla, but very little real gains in a street/strip
>combination. The trade offs may include poor cooling and low alternator
>voltage. I would think the real killer for the Turbo car is the low
>voltage, what with the ECM, all the sensors, high energy coil packs, high
>pressure electric fuel pump, injectors, power accessories, etc.
Don't skimp when feeding them, it will really cost you.

There was an article in Circle Track mag awhile back where Steward Pumps
build a water pump dyno to see what the story was on water pumps. The
worst pump consumed about 20 hp. His racing pumps were down around 8 hp.
Underdriving MIGHT help IF you have extra cooling capacity AND can cool adequately at low speed (if you even need
to, of course. Don't neglect the need to keep head temperatures as
constant as possible while assessing whether you have excess flow.

[Sparky2263]

Turning the armature in itself is just like turning a idler pulley, negligible.

So it is 100% X amount of horsepower to create X amount of amps, aruging that is stupidity in the least.

How is it going to create a higher RPM at best you hope to reach the max rpm faster!

There is nothing to gain by spinning them slower.


What more can I say? You obviously know what you know as do I. "A man convinced against his will is of the same opinion still". A very smart man said that.

For everyone else here, I have quoted those statements which are dead wrong. Ck. it out yourselves, I've stated my case and am done with this thread.

[jharrison]

I like the pulleys I have installed. I felt a difference, I would however recommend one with a 1 7/8" alternator pulley just to keep your alternator up to speed for amps, e-fans and other loads . If you can live with a lower alt output don't get a set with the overdrive alt pulley. I am running the March Power & Amp series.

[biglouie_underpressure]

I'd like to purchase just the crank pulley. Does anyone sell it like that?
i told you i had a underdrive crank pulley a year ago!

[ZR1-S10]

Also keep in mind the smaller crank weighs less. Evey pound of rotational mass you remove is worth 2.7hp.

[03 Rado]

Also keep in mind the smaller crank weighs less. Evey pound of rotational mass you remove is worth 2.7hp.

I have no idea where you may have gotten that from, but freeing up weight in rotational mass changes torque, which then over rpm you could convert that to h.p. But it isnt anywhere near close to that number scenerio. Going to and aluminum flywheel on the average good aluminum flywheel against a steel one yeilds around a 20 lb difference which translates into 8.8 ft lbs gain.

Hell your gonna look for savings in that arena then lighten up the wheel and tire combos etc!

[ZR1-S10]

Well maybe it is torque, anyway it's still an improvment (and more then losing sprung or unsprung weight). As for a lighter wheel and tire combo, sure I am, It's just a underdrive pulley is going to cost alot less and still give some improvment. When trying to get to 500hp I'll take eveything I can get, and I also beleve in a compete setup so if I'm going to light'n one thing I'll try and light'n eveything within reason.

[biglouie_underpressure]

Well maybe it is torque, anyway it's still an improvment (and more then losing sprung or unsprung weight). As for a lighter wheel and tire combo, sure I am, It's just a underdrive pulley is going to cost alot less and still give some improvment. When trying to get to 500hp I'll take eveything I can get, and I also beleve in a compete setup so if I'm going to light'n one thing I'll try and light'n eveything within reason.
aren't you planning on running a s/c? If so i believe boost pressure would change.

[ZR1-S10]

Yes I'm going to put on a Wynjammer. I already have the underdrive pulleys and I hope to keep the crank pulley and have Al make a custom S/C pulley soo I can run the right amount of boost.

[20Xtreme02]

I also run the March Power and Amp pullies although I'm going to go back to the stock alternator pully for another .10 horsepower. ( :-{ I ) I don't race so can't provide exact improvement numbers. Do I feel an increase in performance in the seat of my pants? No, but I'm old, maybe my pants are numb. Do I feel pride and a sense of accomplishment by completing a performance mod on my car? Yes. Was it worth $75.00? Sure, I've spent more money on less useful things before and I supported the Planet store. Moding YOUR vehicle is a personal thing. Do what YOU want.

[biglouie_underpressure]

Yes I'm going to put on a Wynjammer. I already have the underdrive pulleys and I hope to keep the crank pulley and have Al make a custom S/C pulley soo I can run the right amount of boost.
how much boost you plan on running? is it really worth custom pulleys to make that work?

[Minitrucker]

I would think it is worth it.

[slowzq8]

just run a 9 psi pulley and see what it gives you. lol