Any body running a set of March Underdrive Power Amp pulleys on a 305 TPI auto car. 88 to 92? Just wondering if they made any difference in performance or if it's just snake oil. Also any charging problems with the running the under drive pulleys

 

I got a set of underdrive pulleys for the crankshaft & alternator, but I don't know the brand name. They don't give you the kind of horsepower they advertise (nothing ever does) but it seemed to me like they made a slight difference. I haven't had any charging problems out of them so they certainly aren't hurting anything..

 

One of my first mods and the only problem is the lights dim when I'm stopped.But as soon as I get moving everythings good.

 

[rant mode]

If you like baking your alternator, underdrives are a really, really good way to do that. Higher output load at reduced RPM (less fan air) can really heat up the copper. Factory trained, experienced, educated, and degreed electrical, thermodynamic, and mechanical engineers likely spent weeks determining the proper sheave ratio for adequate alternator function and cooling at the lowest programmed target idle RPM, while still preventing rotor overspeed at peak RPM. Considering factors like weather induced drive slippage, peak load conditions from low batteries, failsafe/backup mode idles, and other extraneous factors, they probably got it about right.

Their countless man hours of research, and unmatched understanding of the operation of the alternators they design and build as they integrate to the entire vehicle as a system can be totally erased by only a tiny dose of "Beavis and Butthead" engineering which only addresses one aspect of the operation.

If you want to slow down the steering pump and add unnecessary strain to it at low RPM operation (when you need the greatest assist pressure), or want to slow down the water pump (and risk cooling issues), go ahead. But don't screw with the alternator drive.

At least, I wouldn't. The extra 2-3 HP you might get is not worth the risks, and certainly not a good HP per $$ modification compared to many other potential mods. Unfortunately, it's relatively easy to do, so many people try to take the low-hanging fruit first instead of making truly meaningful modifications.

[/rant]

 

I ran the power and amp series pulleys on my 88 L98 car. I can't say I noticed a big difference, I think I may have noticed a little bit though.

I never had any problems with them as far as charging, I think the whole point of them is that the smaller alt pulley keeps the same ratio as stock.

I'd probably spend the money somewhere else though.

 

I have ran just the crank underdrive pulley which did dim the lights at idle and have ran the power and amp version which has a smaller alternator pulley to bring it up to proper speed so to speak and the lights do not dim with this setup.

Neither will fry your alternator either. They do exactly as advertised with no downside.

 

vader, doesnt the fan run at the same speed as your alternator? so as your putting more current in at low RPM, your fan is also puttin in more air, the pulleys just create an illusion that your alternator is at higher rpm when its not. unless having it run at a high RPM all the time is bad then i dont see how it couldnt cool itself down.

EDIT: arent underdrive pulleys the same ratio as stock pulleys? (or close to it at least), i thought it was just designed because its less rotating mass.

 

If the "Power Amp" series is used, it at least maintains the alternator drive ratio. The only concern with that is the necessarily smaller diameter further decreases the already marginal minimum wrap and radius of the poly-V belt. Every belt has a minimum radius, and every belt drive system (or chain,for that matter) has a minimum "wrap" to provide adequate power transmission without slippage and loss, overheating and wear, etc. You can bet the factory deisnged the systems with consideration for accepted power transmission engineering concepts. I'd guess that the aftermarket has paid less attention to that, since there is no warranty.

Once a mass is at a rotational speed, power required to keep it turning is the same, so the material is less significant than the marketers selling aluminum would have you believe. The lighter mass only makes a difference on acceleration.

Another detriment is the faster wear of pure aluminum sheaves compared to steel. That starts to cost in belt drive efficiency.

The ideal sheave would be an aluminum or magnesium hub with a thin. hardened steel ring to accept the belt. Anyone found those?

 

In order for your car to go faster it has to accelerate, so lighter rotating mass durring acceleration would obivously make it accelerate faster, if your gonna slag rotating mass then why are there carbon fiber driveshafts...

 

You are knowledgable for sure but aren't you overanalyzing this a bit ? Both of mine haven't cause a bit of problems with many miles on the one with only the underdrive crank pulley.

 

i have the power and amp set on my l98 car (crank and alt.) i didnt really notice a big difference just from those, but those and a slp cold air are the only mods to my car right now iand it was runnin consistant bottom 14's this past summer (14.23 best)

 

You may not notice anything the same way you do not notice 2-3 HP. In the long run you may get lets say 60k out of your water pump instead of 150k
You may only get 70k out of your power steering instead of 200k. It is an unimportant risk. You are creating a problem to make you think you are solving another.

Good example would be people who take the screens out of their MAF. The pay off is that it gives you a couple HP, but the MAF is such a delicate instrument it drastically shortens its' life.

Where are you going to be when that water pump fails? Somewhere safe I hope.

 

Had the March "power n amp". Put it on...slowed down the A/C....baked in the car...car didn't go any faster.........took it all out......enjoyed the A/C.........stopped baking........sold the pulley's to a kid (let him bake)........'nuff said.

 

I've had the two pc. power and amp on my 91' 5.7L with no problems in 8 years. It might show some HP on a dyno, but nothing you can feel.

 

I have got the three piece regular march set on my LO3 and the only problem I had with them is the fact that one week after I put the car on the road, the alternator went out, but after putting another back on, nothing else really went wrong. The only concern was that there was no charge at idle.

 

I put a kit on my '85 IROC WAY back; like about '88-'89. Didn't really have any negatives for the time it was on, except for constant squeal/harmonics problem. It seemed to have better response.

Contacted them, swapped in a different set, same deal.

The sheaves were DEAD IN-LINE, new belt, not slipping, just a high pitched harmonic I couldn't get rid of. Journeyman Toolmaker; there was no mechanical problem with the install!

The Tech/Customer service guy at March was dyck on the phone, like a HUGE coke-head would be. I returned the second set for a refund.

My recommendation: find other venues for power increases.

 

Many people use them without any serious problems. My only points were that there are potential problems arising from their use, and that the power "liberated" by underdrives in the real world is nowhere close to the optomistic estimates often quoted by the sellers. The real HP/$$ numbers aren't there, whether or not they cause any problems for anyone installing them, and there are better ways to make more power for the same money spent.