I was just wondering...how big of a difference would I feel with Sub frame Conntectors, an underdrive pulley, and an aluminum driveshaft. And then what about if I changed my rearend from 3.42 to 3.73 gears on top of that other stuff

 

A lighter wallet would be the biggest defference.
1) SFC's a tighter car
2) Underdrive pulley= problems
3) Alum=lighter drivetrain (good)
4) 3:42 gears a good mod

 

You should get a decent amount of torque recovered to you. The sfc's will help the chassis. I have done the underdrives and the gears (2.73 to 3.23). Those alone got my torque at the rear wheels to have the stock torque numbers at the flywheel.

Note the gain showed itself on the dyno in terms of torque. Not bad considering I stuck on my heavier 16 inch IROC-Z rims too when I did the dyno.

If you get past the lighter wallet, underdrives aren't that bad. I've been running underdrive pulleys for almost 10 months now with no real major issues. The only condition is that I'm running only the underdrive crank pulley with the stock alternator pulley.

The only problems I have is when I am in gear and have ALL possible items on, defroster, headlights, brake lights, heater or A/C on max, windshield wipers, turn signal, coolant fan on and radio on my voltage will be down around 10-12 volts, obviously using battery power at that point.

On top of this I'm running a 45 gap on my plugs to force it to eat even more current to keep the engine going. Is it a really a problem? No, since that set of conditions lasts as long as a stoplight at best. On top of that I can just bump it into neutral and at a 675-700 idle in neutral is enough to give me 13-14 volts again.

You can offset this completely by getting a smaller than stock alternator pulley (what you get in the power and amp set from March) and thus keep the ratio for the alternator stock and get underdrive benefits.

 

So if you install an underdrive at the crank, and an overdrive at the alternator, how much have you gained? Unless you are turnnig the steering wheel, the alternator is your biggest load. The water pump really doesn't take that much power, and the steering pump losses are very low when it is just recirculating.

The exta plug gap might take an additional 2-3 amps at high RPM, worst case. I'm with Z-28. Save the money from the underdrive sheaves and put it in gears or a torque converter.

 

whats so bad about under drive pulleys. i was thinking of getting a set alt/water/crank for my 383, but maybe not