Does this modification work, and is there any real benefit from it, better for the car?.

85-88 V6 POWER PULLEY KIT Harness the wasted power from your belt driven accessories. Bring those RPM's up quicker while keeping your car within it's power band. Also good for an approximate 6% gain in HP. Kit includes: 24% smaller crank pulley, new belts and bolts. Part # 52304 Price: $79.95

Actually I kinda have to disagree with Blair on this one.  I have the double pulley kit.  On a 2.8 there is a noticeable difference in how the engine revs up.  Someone on PFF did the conversion on there car and gained 1-2 tenths in the quarter mile. (thats a car length in a street race) 

I would probably check with ASP Racing, http://www.aspracing.com/ - http://www.aspracing.com/  as they are the people that the Fiero Store buys from.  I believe they are the only ones selling the double under drive kit.  (you get a smaller crank pulley and a larger alternator pulley. 

Fiero

Year	Engine	Pulley Description	Full Charge	- Info-	Hard CoatBlack Alum
85-88	2.8	25% Crank	900 RPM	javascript makeRemote'images/asp845200.jpg'">  http://www.aspracing.com/ins845200.htm">	ASP845200 https://www.aspracing.com/ezRetail/search/view.php?msg_id=296" target=blank> $59.95
85-88	2.8	25% Crank23% Alternator	1100 RPM	javascript makeRemote'images/asp845202.jpg'">  http://www.aspracing.com/ins845202.htm">	ASP845202 https://www.aspracing.com/ezRetail/search/view.php?msg_id=297" target=blank> $79.95

Click-On Price to Order

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Is is better for the engine, mileage, etc. as they say?.  I placed my order already and if I would do this upgrade, I would go the full route and double pulley.

Thanks guys

Well in my observation, I did get better gas mileage, better overall power and the car just seemed to run better.

This pulley set is NOT a good idea if you spend a lot of time at really low revs idling. Especially if you have big stereo (600 watts or more)  I had to have Craker burn me a new chip that had an 1100 rpm idle rather than the 900-1000 that stock is.    With all the accessories on, heater on high, headlights on, at idle with my foot on the brake, the voltage would drop to 12v, just slightly below the middle on the gauge.  With a chip moved to 1100rpms that issue went away.  The car never failed to start, but it botherd me seeing the voltage down under those circumstances.

As a side note, due to the water pump moving slower and alternator moving slower, it aids in the bearing life if you drive in a spirited manor.

Oh and one last thing, rotating mass is reduced do to the new pulleys being aluminum rather than steel.  I also found less tendency for the belts and pulleys to glaze over.  That is one of the reasons you never hear belt squeal from my car. 

Copied from the ASP site.

What do Under drive Pulleys do? Under drive pulley systems increase engine horsepower by reducing the amount of power required to drive external engine accessories. For example, the alternator, power steering, water pump and air compressor rob horsepower from the engine. By replacing factory-sized crank and accessory drive pulleys with a resized pulley, the accessories are slowed, resulting in more horsepower available to the drive wheels. Typically, a set of Auto Specialties street pulleys will increase horsepower by 12-15, and increase mileage by 2 to 3 MPG. All pulleys are manufactured from Billet Steel or Aluminum, exceeding factory quality.