KJ Jones Senior Technical Editor
January 1, 2009
Photos By: KJ Jones
A smooth, free-spinning impeller is the mark of a happy centrifugal supercharger. Paxton's lead blower tech, Greg Dawley, cleaned, inspected, and freshened our T-top coupe's Novi 2000 with new seals and bearings, and then replaced the blower's volute with the straight-discharge piece we need for an intercooler system we hope to install fairly soon.

Horse Sense: We oftentimes find ourselves marveling at the infinite wisdom (Yeah, right.-Ed.) of our leader, Editor Steve Turner, who always seems to have the right view on challenging issues. Steve believes project cars are never really "finished" when it comes to making changes and upgrades, as long as they're still in our possession. Since our last report on Project T-top Coupe ("Score to Settle," Aug '08, p. 102), we've been battling with the dilemma of when we're finally going to say "that's enough" in regard to this project. For now, the answer is never. And with that said, read on to find out the new direction we're going in with our rare coupe.

Now that we've met-and in many cases, surpassed-nearly all of the appearance and performance goals that were set when the Fox-rod resto odyssey of our '86 T-top LX coupe began, many of you are probably wondering what's next for the project car. At this point, that's a great question.

If someone were to ask us whether we're happy with the 830 non-intercooled, streetable horsepower and 9-second performance that our Paxton Novi 2000-blown coupe has displayed on the dragstrip, the quick and definitive answer would be "of course we're happy." However, if the same person asks if we are satisfied with that performance, at this point, an affirmative probably won't come so quickly.

The reason we're somewhat hesitant to say we are fully satisfied with the T-top coupe is because deep down we know that despite the flashes of brilliance it has displayed thus far, there's another performance plateau our rare Fox trunk can reach. With that said, we're proud to let you know that Project T-top Coupe lives on. Our new mission is to somehow, some way achieve 1,000 hp "at the feet" (it's new slang for rear-wheel-horsepower that we think is pretty cool) of our street/strip project car. At this point, we're so close to laying down a full grand that not trying to get it just doesn't make any sense for power-mad 'Stangbangers like us.

You'll notice we stress the fact that our coupe's A.R.E. Performance [(805) 583-0602] 350ci, supercharged bullet puts out crazy oats without the benefit of an intercooler. That's right; you can almost say we're doing things NMRA EFI Renegade style, with the major difference being that we drive the T-top coupe regularly on the boulevards and streets of Southern California's San Fernando Valley instead of limiting it to the 1,320-foot confines of the dragstrip.

After giving our blower's exterior and case an overall visual inspection, Greg removes this oil-supply nozzle and checks its screen for metal particles or other debris. Blockage in this tube can lead to catastrophic failure of the blower by way of non-lubricated internals that succumb to excessive heat. Finding debris in this area is an indicator that there may be serious problems with the supercharger itself or the engine, as the oil running into this tube comes directly from the engine's oil pan.

Our quest for 1,000 hp is highlighted by a major addition to the supercharger system. If you're guessing "intercooler," you're absolutely right. Yes, we've decided to plumb a 'cooler into the Novi's ductwork. An intercooler will help bring inlet-air temps down, as well as make a considerable difference in the blower's efficiency and ability to produce more power. Early forecasts estimate we could see gains of more than 100 hp with an intercooler in place. Sure, we know it's a guesstimate and the gain could be less. But at this point, we also know we need to install an intercooler to see any improvement in the coupe's performance on the chassis dyno.

Our first step toward making the transition doesn't involve the intercooler just yet. The first order of business is to address our Novi 2000's internal and external needs, and the only way to do that is by letting the experts at Paxton handle things.

Changing the supercharger's volute (the snail-shell-shaped, cast-aluminum housing in which a high-speed impeller generates boost from inlet air and forces it into the engine through a discharge tube) from curved discharge to straight discharge is our primary need. The coupe's Novi currently has a curved-discharge volute, which expels supercharged air from the back of the unit. With an intercooler mounted at the lower-front portion of the project car, the setup requires a volute with a discharge that doesn't curve and can be pointed toward the passenger-side fender.

While the volute swap is the primary agenda item for our project coupe's Novi, it actually takes a back seat to the subject matter we're focusing on in this report, which we feel is much more important to those of you who have a Paxton (or Vortech) supercharger on your 'Stang and want to make sure they're always in tip-top shape.

With the volute removed, Greg checks the index mark on our Novi's impeller to see if it has spun abnormally or the shaft has twisted.

If you haven't figured it out yet, we're talking about supercharger maintenance. Keeping tabs on a blower's mechanical condition is something we suspect many of you don't give much thought until the 'charger no longer functions as it should (decreased boost, leaking, abnormal noise) or experiences a catastrophic failure of some sort, which could possibly lead to engine damage as well. So, with our blower already at Paxton for the volute transformation, there's no better time than the present to also have the unit gone over (thoroughly inspected, cleaned, and rejuvenated with new seals, bearings, and shims, as well as gears or other hard parts if necessary) by the company's factory-trained supercharger specialists. When you consider the extreme heat and high-rpm duress that superchargers endure when you're really getting after it in your Pony-on the street and especially at the track-we think it's critical that you pay attention to the blower and follow our lead by having it serviced before the worst happens.

We often talk about projects and upgrades that are easy enough for do-it-yourself-minded enthusiasts. Contrary to what you may think, servicing a blower is not among those easy tasks: It should be left to the experts at Paxton/Vortech.

Greg Dawley is the supercharger guru helping us. Greg is one of two technicians at Paxton who are responsible for all of the supercharger inspections and by-hand rebuilds performed once a blower is received.

Once trueness is verified, the impeller is removed from its base.

Our Novi wasn't critical, but thanks to the 65,000-rpm impeller speed it sees on the dyno, Greg noticed that the lower bearing on its impeller shaft was a bit rougher than it should be, and we also had some minor leakage at the impeller seal. We use a 3-inch race pulley to achieve 20 psi of boost and this type of impeller speed at 6,800-7,000 engine rpm. An 8-psi, street Novi 2000's normal rev limit is about 55,000 rpm.

The following photos and captions take you inside the blower, if you will, and detail the factory maintenance process for our Novi 2000. We shadowed Greg's every move, and learned quite a few interesting things about the type of damage a supercharger can incur-and more importantly, things to look or listen for to determine whether your blower is damaged.

This steel seal pulls double duty in the supercharger's operation by retaining the impeller's rubber seal (and completing the overall mechanical seal between the transmission and impeller's mating ring) and also creating clearance between the back of the impeller and the volute. A blower won't function properly if this spacer is not in place or is the wrong size.

Greg lifts the Novi's transmission cover off its base for access to the gears inside. Note that the cover must be removed evenly, and special tools are required for its extraction to prevent damage to either mating surface or their locating dowels. This is why we think it's best that you send your blower to Paxton for service or repair before trying such work on your own.

The transmission represents ground zero in a centrifugal supercharger. Greg removes our blower's pulley and impeller gearsets by pulling them straight up and out of the case simultaneously to avoid damaging teeth on either gear. Paxton shaft and gear combinations are machined as one piece as opposed to gears pressed onto the shafts separately, as they are done with Vortech superchargers.

Bearings are inspected both visually (for scratches, scoring, burning, or metal filaments attached to their surface) and by turning each bearing along its shaft. Greg detects roughness in the case-side lower bearing on our supercharger's impeller shaft, which means there could be some metal inside the bearing or it may be wearing out. A tight belt and high pulley speed are forces that affect bearing wear. It's good that we're catching it now.

Greg uses Paxton's proprietary bearing tools to remove and install bearings for our Novi's freshen-up. The fixtures are all produced in-house and are essential to this part of a blower's build process.

This is the collection of parts included in Paxton's Novi 2000 Minor Service ($424.95 for parts and labor). The maintenance kit includes all of the bearings, seals, O-rings, shims, and fasteners necessary for making a blower look and, more importantly, function like new. Unfortunately, the freshen-up procedure isn't one that we suggest you try and handle yourself. Leave this job to the experts at Paxton. Having your blower returned to its original condition by a trained technician is well worth the reasonable investment (compared to the price of a new supercharger). We're told it takes about 7 to 10 days from the time a blower is received, then it's back in its owner's hands and ready to reinstall on an engine.

Before reassembly, the blower's case and innards are thoroughly cleaned in a 140-degree, high-pressure cleaning tank...

...and inspected again for any damage that may not have been discernable during disassembly.

The blower housing is placed in a 225-degree oven for about 15 minutes to heat the supercharger housing's bearing bores. This ensures that the bearings will fit properly inside the bores.

New bearings are lubed with oil and pressed onto each shaft; the new mechanical seal is pressed in place using Paxton's proprietary bearing and seal tools.

Internal parts of interest are the "wave springs" that sit atop the rear bearing ring on the impeller shaft (right), and help keep the bearings loaded once the gear case is sealed. The shim on top of the wave spring provides the necessary clearance between the bearings and the case. Wave washers are also used for preload on the pulley shaft.

Greg uses this depth gauge on our blower's new volute to measure the depth of the impeller when it's completely flush against the volute. From this measurement, Greg uses a formula to calculate which size spacer is required, as well as the setup height of the impeller.

A special fixture for the Novi 2000 is used to hold the blower in place and lock the impeller shaft while Greg torques down the impeller's fastening nut. Don't mistake this apparatus for a vise-it's not. It's another Paxton-designed piece of equipment that is used exclusively for this purpose to prevent any damage to the supercharger during this tightening process.

Greg pressure-tests our blower to ensure it is fully sealed and not leaking any air pressure. The needle on the pressure gauge holds steady at nearly 15 psi, so the project car's supercharger is signed off as ready to rock.

On the left is the curved-discharge volute; the unit on the right is our completed Novi 2000 with its new, straight-discharge volute. The volute measures 4 inches on the intake side and 3 inches at the discharge opening. If you want Paxton to perform the volute swap only (although we highly recommend having your blower serviced, too), the conversion from curved-to-straight discharge will set you back $238.95 for parts and labor.

Greg checks the impeller to confirm that its points are good and there is no indication that it has touched down inside the volute.

Every supercharger, even our project car's Novi 2000, has critical operating limits that must be acknowledged if you expect the blower to have any type of longevity.

"Once you start to take a blower above our recommended maximum rpm, its efficiency starts to fall off, oftentimes to a point where we recommend moving up to another product that will give you the performance (blower speed and boost production) you want without imposing the same type of stress on its internal parts or generating the type of heat that can lead to damage or failure," says Ricky Best, Paxton/Vortech's Motorsports and Media relations manager. "A supercharger really is like a little book. Upon inspection, we're able to see where a failure has occurred and usually pinpoint exactly why (excessive belt tension, insufficient oiling, and so on). If you change your oil at regular intervals and take good care of your supercharger-don't overspin it, and keep it in its operating rpm range-there's no reason why the blower won't last 80,000 to 100,000 miles, but sending it to us for an inspection and refreshing is good, inexpensive insurance," Ricky says.

A wear mark similar to this one in the bearing bore for the supercharger's upper pulley bearing is a tell-tale indicator that the belt has been grossly overtightened. Since there is more load on this part of the bearing, heat builds up in this area and causes premature failure of the bearing.

Each supercharger that is returned for maintenance service is evaluated using this checklist that contains possible problems and the technician's assessment of the unit's external and internal condition.

The bent points on the impeller (left) and wear ring that has been ground into the volute in the background (right) are prime examples of an impeller that has "touched down" inside the volute. A touch-down is usually caused by an improperly sized bypass valve, and it isn't the kind deserving of a celebratory dance. If the bypass valve is too small, there's no way it can handle more than 8 psi of air. When you've got 10-plus psi being fed to a small bypass by a 3-inch discharge tube, the excessive air pressure is forced back into the supercharger and up under the impeller when the throttle is slammed shut. This backpressure forces the impeller off its base, sending it crashing into the volute at high speed.