S197 V6 Mustang Bolt-On Test

Underdrive Pulley

Just one pulley--the crank pulley--is underdriven on V-6 underdrive pulleykits. The one-piece pulley/harmonic damper assembly is exchanged withthe stock damper, along with a shorter serpentine drive belt. GTR sellsthe ASP Racing pulley/damper for 4.0-liter V-6s. ASP says this 25percent underdrive pulley provides charging voltage at only 850 rpm.

And then there was the underdrive pulley. The 4.0-liter, like the3.8-liter that preceded it, is one of those engines where the underdrivepulley is only the crank pulley.

Again like the 3.8-liter, the 4.0-liter crank pulley is integral--onepiece--with the harmonic damper. Installing "underdrive pulleys" on a V-6Mustang, only changes the harmonic damper. But pulling that damper isgenerally a difficult job.

It would have been pretty simple, except the bolt supplied with thedamper to mate with the harmonic damper puller was too short. All sortsof time-wasting effort resulted, with the final fix being thefabrication of our own bolt. This wasn't the easiest thing, as thecombination of thread series, diameter and length is oddball, but it gotmuch easier when we realized a modular V-8 head bolt was correct, savefor the length. As GTR has old modular head bolts on hand, after a pairof cuts with the chop saw and some quality time with the smoke wrenchand we were in business.

We have to say, after hours of messing around all the effort provedworth it. The power jumped to 204 rwhp, then backed up at 203 rwhp, then203 rwhp again and we figured that must be what it runs, but we hit itagain just to see what it would do when totally heat soaked. It maxed at204.5 rwhp.

To help with damper removal, ASP provides three bolts with its damper.As harmonic damper pullers vary widely in their design and travel, thesebolts probably work OK with many pullers, but the central bolt, whichpushes against the harmonic damper bolt, was not.	To get our damper puller to provide the last inch of necessary travel,GTR had to make a longer bolt. This was done by starting with a modularcylinder head bolt, cutting several inches out of it, then welding ittogether again. A bushing was used to provide strength over the weldedsection.	Because the smaller-diameter crank pulley provides surprisingly reducedpulley perimeter, a new, shorter serpentine belt is required. The beltis not supplied with the pulley and must be bought separately.
It doesn't take long to remove the fan shroud and set aside the radiatorheader tank. The reward is huge space dividends when changing on theharmonic damper.	Admittedly a real pain in the neck, the only real challenge to replacinga harmonic damper is finding and rigging a damper puller that works. Thebiggest issue is having enough travel from the puller so it gets thedamper all the way off the crank. This is the puller and rig thatfinally did the deed for us.	There's no missing the smaller ASP pulley when the stocker is laid nextto it. By changing the crank pulley, all accessories are automaticallyunderdriven. In this case it was underdriven by 25 percent.
Ricardo prepared the ASP damper for installation by lubricating thedamper bore with silicone grease, and applying a dap of silicone sealerto the keyway as shown here. The silicone combats the possibility of oilseeping along the keyway to form a leak.

All Together Now

Thanks to the cold-air intake and underdrive pulley, we gained a solid20 hp at the V-6's wheels. The muffler didn't hurt and might help with ablower, while higher octane fuel was a waste until more ignition timingarrived due to electronic tuning. All told, it was a 9.8 percent gainin horsepower, and that's just right for a daily driver. It's enoughpower to feel, but not enough to ruin good manners.

For our tastes, we'd go with the cold air and underdrive pulley and saveour muffler money for when forced induction is fitted. Considering we'dhave a V-6 Mustang around for economical, yet fun, daily transport, thedefinite noise increase from the muffler isn't in keeping with the car'suse to begin with. Without a big power gain, why bother? But we're usand you're you, and if more sound makes it more fun, then there's youranswer.

Another tactic would be to fit a true dual exhaust, as V-6 enginesprefer two separate three-cylinder exhaust systems with no H or Xcrossovers. While more expensive, such systems can definitely aid powerwith forced induction and often sound more V-8-like than rasp-can giventhe Mustang's generous six-cylinder displacement. It just depends onwhat you're listening for.

In any case, bolt-ons and the 4.0-liter V-6 are a good thing.