I've got an 89 firebird and 91 camaro both with the L98 5.7L 350. Both are 100% stock. I want to put under drive pulleys on both of them, but some people tell me they are a waste of money. Is this true. If not what type should I go with. I have seen some that have 2 piece and 3 piece pulley sets. What would be the better set to go with and manufacture. Are there any draw backs to putting them on a car. Such as cooling, charging etc. I was looking at the march, or jet chip pulleys. Will I notice a difference in power? I know they don't make hp, but they free hp up. Thanks.

 

What are trying to underdrive? I think the only thing anyone should actually be doing this to is the water pump pulley, so it works better at high r(s)pm.

 

I was using the March underdrive pulleys on my minirammed 385. I had both the crank underdrive and the alternator underdrive pulleys, and what I discovered is that everything worked as advertised except the alternator. I had to keep RPM above 1000 to enable charging of the battery. My alternator recently failed at a high-speed driving event at Gingerman Raceway and I swapped it out for an Autozone special with conventional pulley. Now it stays in a charge condition down to 500 RPM. Much better: I now have to readjust my engine idle speed, which is okay by me! I found that there wasn't much measureable difference in terms of power (certainly nothing I could feel), and the new alternator seems to do just fine at extended speeds above 6000 RPM when at the track. I highly recommend the crank pulley but would pass on installing an alternator underdrive.

 

Powermaster's website strongly recommends against underdrive pulleys.

Personally I prefer a fully charged electrical system myself.

 

What I'd be interested in doing is putting an underdrive pulley on the crank and an overdrive pulley on the alternator. That way the alternator spins as the factory intended, but the other accessories are still slowed down. Should be worth ~5hp and should pose no other issues, besides a slightly reduced-capacity air conditioning system.

 

If you change the pulley ratios by overdriving the alternator to compensate for the underdrive crank pulley, then I suspect there is no net change in horsepower. I'd recommend a crank underdrive pulley only, which will slow down all accessories. However I do not recommend the additional underdriven alternator pulley for the reasons I experienced above. With the crank underdrive pulley alone, I have experienced no net problems. Alternator is charging fine, power steering works as advertised, and the waterpump is a pumpin'.

 

If that were true, wouldn't it mean that the alternator takes significantly more effort to turn than the water pump, power steering, and air conditioning combined? Seems to me that the alternator is the smallest drag of all four, and that underdriving just those three would provide the most significant benefits.

 

14.5V * 105 Amps = 1.45 Kilowatts * efficiencyfudgefactor * 1.341 HP/1KW = your power requirements.

Figure in a fudge factor of ten percent efficiency loss due to heat (eff=1.10) and the power requirement of the alternator is 2.25 Horsepower. That would be the bare minimum power requirement. There are also efficiency losses in the bearings, regulators, diodes, serpentine belt friction, excitation coil resistance, etcetera. I don't know what those efficiency losses are, but wouldnt doubt they add up to another horsepower or two. The alternator regulates itself through the SENSE wire, which boosts the excitation coil to keep the voltage output constant. In essence, the alternator adjusts the magnetic field, making it stronger as necessary to keep the voltage constant. The larger the current requirement to keep a stable voltage, the stronger the magnetic field becomes to force the electrons down the wire through the diodes. The stronger the magnetic field, the more resistance is felt by the drive belt. It's a much more dynamic load compared to a waterpump, for instance, which increases load linearly until the vanes reach cavitation, at which time the load actualy drops off as the vanes pump against vacuum. Power steering loads are non-linear and vary depending on engine RPM and rack & pinion assist requirements. However, I suspect that when you need the electric current to hold the clutch closed on your A/C compressor, and you are stressing your ignition system, plus dumping current into the fuel pump, injectors, and stereo system, the alternator has as much load requirement as a water pump or even power steering pump, for that matter.

That probably muddies the water a little, and we should probably move to another thread if we want to discuss such things. In the end, I really don't think it would matter either way, because 5 HP is not really something you can *feel* when comparing 295 to 300 HP.

 

I bought a kit of ebay about 2 months ago and installed it. No problems what so ever. It was the 2 pulley kit. One smaller one for the crank and one for the alternator. The smaller alternator pulley, Is NOT under-driving the alternator, it is OVER-driving it. It is supplied to speed it back up. You do not want to install just the crank pulley. That will cause electrical problems.

The smaller pulley on the crank means the belt moves a shorter distance per revolution. Just like taking a 30" tire and putting it beside a 26" tire. In one revolution the 30" will be further along. So the smaller crank pulley means that the belt moves shorter, rotating the accessories less, creating less drag, and in return freeing up horsepower.

However, the small pulley on the alternator has a similar effect, but for different reasons. A small pulley will turn the alternator faster than a larger pulley at the same belt speed. Since the belt is slower with the smaller crank pulley, a smaller alternator pulley is included to speed the alternator back up.

Most kits are like this. Not sure why some of you think it is a bad thing. Maybe you are just confused to how it works. In PHR (could have been another car mag) with either the street sweeper chevelle or that f*rd project, they did infact underdrive the alternator by installing a bigger pulley. They were clearly looking for more power only.

In short, if you install a smaller crank pulley, be sure to install a smaller alternator pulley.

 

My kit came with a larger alternator pulley. Mine was an underdrive kit for L98 serpentine belt systems that I bought during the summer of 2000, when designing my minirammed 385. ...and no, I was never, ever confused. However, thanks for the clarification anyway.

Here's its equivilant at summit racing equipment:
http://store.summitracing.com/partde...5&autoview=sku

Performance ratio:


It looks as if you can get the fifty buck "standard ratio" pulley set for $54, or the "performance ratio" pulley set for $110. I have the performance ratio set. Now, I guess I have a hybrid between standard ratio and performance ratio. It works just fine now, thank you. No need for a smaller alternator pulley. In fact, what you dont know is that I also use a 14 pound, 15 AH mini-battery to power my car.(Genesis gell-cell). If anyone would have had troubles due to insufficient charging, it would have been me. I've been using the Genesis-series since 2004 and it's never failed to start the car.

Standard ratio:


You better take another look at Summit's underdrive catalog, by the way. The "standard ratio" shown above is the only one in their catalog with the smaller alternator pulley. The rest all have the larger diameter alternator pulley. Therefore, it seems as if the larger pulley may be more popular than you think.

 

Have the stockers cleaned and powdercoated a nice color. It'd be worth more.

 

For the small horsepower gain and the problems they cause on a street car, they are not worth the money or the problems.

 

ws6, most kits I have seen, have been like the standard you posted. But thats just me. And I stand corrected on the popularity. I wasnt disagreeing with anyone, Ive just seen people before that would argue that smaller pulleys underdrive everything. I was just trying to help clarify everything.

wow $50 more dollars for almost the exact same kit, but with alittle larger pulley? Thats a heck of a price jump

 

Well, it sounds like I will forget about the underdrive pulleys. It seems like most of you have had problems or not seen alot of gain with them. Thanks everybody for your help.