5.0 Underdrive Pulleys
Having the right underdrive pulleys can be the difference of 10-15 horses
From the December, 2012 issue of 5.0 Mustang & Super Fords
By KJ Jones
Photography by KJ Jones
A few months and issues of your favorite Mustang magazine have gone by, and we hope you've had a chance to read and absorb the cover story of our Oct. '12 issue. In the article (“The Main Event,” p. 52), your scribe takes representative 'Stangs from four of our most popular Mustang platforms, and evaluates the percentage-difference in performance gain for each of them with bolt-ons. Our rules of engagement for that effort meant that the parts we used had to be available for each Mustang platform in our control set. Since such pieces are not yet developed for the newest 5.0 Ponies (and we doubt they will be), underdrive wheels didn't make the cut for the battle.
With that said, we're happy to announce that the underdrives' time has come, as this month we're revisiting installation and dyno test of a three-piece pulley set from March Performance (PN 1000-08; $54). While the latest 5.0-liter Mustangs are undisputedly the hotness now, we've noticed there also has been a recent resurgence for the original 5.0-powered Ponies ('79-'93 Foxes), which literally made the underdrive concept famous for our hobby.
For the uninitiated, underdrive pulleys are direct-replacement wheels of varying diameters (smaller crankshaft, larger water pump and alternator) that basically reduce the speed/rpm of such belt-driven engine accessories as the water pump and alternator. The slower pulley speed decreases the amount of parasitic drag on the crankshaft, which ultimately allows the engine to rev quicker, freeing up that engine's inherent horsepower.
While Ricardo Topete of GTR High Performance is adding the March set on a Fox this time (Max Partida's '92 Mustang LX), the installation is simialr on any applicable Pony. The following photos and captions touch on the three-piece pulley set's installation, which actually requires only an hour and handtools that are found in most 'Stangbanger tool collections, save for an impact for the alternator. In addition to those details, we also recommend you pay close attention to the dyno results, which confirm the solid gains.
GTR High Performance’s co-owner...
GTR High Performance’s co-owner and lead technician, Ricardo Topete, tightens down an underdrive crank pulley on the push-rod 5.0 engine in Max Partida’s Fox ’Stang. Often overlooked when basic bolt-ons are being considered, a three-piece set of underdrive pulleys (we’re using steel pieces from March Performance) is a quick and easy upgrade that frees up 10-15 horses at the feet of most ’79-’10 V-8 ‘Stangs.
Here's a look at the three...
Here's a look at the three primary components in March's Performance Series underdrive pulley set for '79-'93 5.0 'Stangs (PN 1000-08; $54). While the system's water pump and alternator wheels are clearly larger in diameter (5-1/2 versus 4-3/4 inches, and 3 versus 2-1/2 inches respectively), a smaller wheel (4-3/4 versus 6 inches) is installed on the crankshaft.
For applications that require...
For applications that require a bit more "show" to go with the performance gained with pulleys, March offers clearcoated, billet-aluminum pieces in its Ultra Series.
Although the operation is definitely easy, installing Fox 5.0 underdrive pulleys is slightly more labor-intensive than, say, bolting on a cold-air system--slightly. However, based on the impressive and consistent horsepower and torque gains that you can pretty much count on seeing with pulleys, we have to say this particular basic upgrade (especially the steel set at less than $60) really delivers.
Max's Calypso Green'92 LX...
Max's Calypso Green'92 LX is yet another Fox in the GTR camp that has not been excessively modified. With only a CAI, 70mm throttle body, and short-tube headers, the Pony laid down 203 horses and 274 lb-ft of torque during our baseline test. We must note, Max's 'Stang is of the AOD variety, so a small concession has to be made for that power-robbing equipment.
Bam! The dyno doesn't lie:...
Bam! The dyno doesn't lie: 11-15 additional rear-wheel horsepower (we saw 16 with Max's 5.0 Pony) makes its presence known with the simple addition of underdrive pulleys.
Once the serpentine belt is...
Once the serpentine belt is removed, unbolting a Fox 5.0's original accessory pulleys is not difficult, nor is installing the new March pulleys. Ricardo replaces the water-pump first. There is no need to drain any water or anti-freeze from the cooling system. The idea of slower pulley speed often raises concerns about the probability of an engine overheating, especially in stop-and-go traffic. While this could happen, it is dependant on the condition of the cooling system. To keep things cool, installing a cooler thermostat (160 degrees) is recommended.
The March pulley set does...
The March pulley set does not require shims, spacer discs, or crankshaft/water-pump modifications. Once installed, the pulleys line up perfectly.
While larger than stock, the...
While larger than stock, the March alternator pulley does not slow alternator speed to a point where its charging ability is compromised, provided the 'Stang's charging system (alternator) is functioning properly. In the event this pulley change promotes lower voltage output, raising the idle is the easiest way to correct the charging rate. It's important to note that this replacement is the only one in the process that requires using an air or electric impact gun, for removing and reinstalling the retaining nut for the pulley.
Inspecting the serpentine...
Inspecting the serpentine belt is a must if you're performing this upgrade on a 'Stang that's long on miles. As you see in this photo, the six-rib belt on Max's engine is worn down to four ribs in some sections.
While still functional (barely),...
While still functional (barely), it's best to nip this potential problem in the bud now by installing a new belt.