Having finished installing Vortech Engineering's centrifugal supercharger system last time (see "Back in Black, Part IV," Oct. '05), we told you that we were almost ready to hit the streets with several psi of aftercooled boost. Hold your breath no longer; the time has come.
On the Road: Driving our Supercharged Goat
At this point I could go into a full-fledged, post-adolescent rant about how awesome the GTO drives now, how the tires won't stop spinning until over 70 mph, and how I would recommend the kit above all others--despite having had no experience whatsoever with other GTO supercharger systems on the market. However, I choose to take a more objective approach in the evaluation of this system.
Observation number one: the tires really won't stop spinning until over 70 mph. Try a 60-mph full-throttle kickdown, and the traction control comes on. This is even with our Nitto Extreme Drag tires, mind you, and in a car that now comes in at 3,980 pounds at the starting line (understandably slightly up from its pre-installation weight).
Observation number two: the car now has a distinct tone that comes with no other type of power adder. The blower gently whines as the car idles, and while at cruising speed, one hears the acoustical marvel of the compressor spinning at many thousands of rpm--quite similar to a ride in a jet airplane. A stab of the throttle followed by a quick let-off results in an evil hiss as air blows through the bypass valve and back out the air filter. Nasty indeed.
Observation number three: the transmission shifts very nicely now--firmer, but not annoying. Vortech says it increased stiffness about 35 percent. Smooth part-throttle shifts combined with firm (but not neck-snapping) full-throttle gear changes yield a well-behaved tranny that's up to whatever kind of driving the pilot is.
Observation number four: everything else on the road seems to have mysteriously lost hundreds of horsepower. One of the first cars to end up in the rearview mirror was a $121,000 Mercedes CL 55 AMG, and I can't tell you how satisfying that was.
Testing for the Numbers
But I stray from my goal of objectivity; let's talk performance in terms that aren't tainted by the human emotion of excitement. You'll recall that before beginning the Vortech install we saw 302.7 hp and 318.5 lb-ft at the rear wheels at TT Performance's Dynojet 224x. At that point in time, the only engine-related aftermarket parts on the car were a SpeedInc air intake and an SLP Loud Mouth exhaust system (we have swapped its mufflers for more aggressive-sounding resonators since our first "Back in Black" installment). Now with the Vortech V-2 in place, the SpeedInc intake had to be retired, so the exhaust is the sole other power-adding part on the car. The results: 447.5 horses and 422.5 lb-ft at the rear wheels. An impressive increase, and far above what Vortech had claimed in its advertising. At the crank, the LS1 now produces 559 horses and 528 lb-ft, a gain of 181 hp at the engine (versus Vortech's advertised 131). Wide smiles abounded in TT Performance's shop that day, let me tell you. Certainly the aftermarket exhaust helped a few extra ponies to escape--thanks to the GTO's exhaust needing to exhale much more flow than would come out of a naturally aspirated LS1--but we're confident the vast majority of this increase would still be seen on a bone-stock car.
The dragstrip is where the kit really proved its propensity for truly impressive increases in speed. Recall that the best numbers we came up with prior to the Vortech install were a 13.20 at 104.9 (which included a custom tune not reflected in the above-quoted baseline dyno numbers). After a failed attempt to get some solid Vortech numbers on a poorly prepped surface at a different racetrack--where a notchback Mustang landed on its roof and we opted to call it quits lest we suffer the same fate--in mid-March, we found success at tried-and-true Raceway Park in Englishtown, New Jersey. After a 10-second First-gear burn, the Nittos bit just fine, not slipping a bit on their way to the 60-foot mark (in 1.88 seconds). The quarter-mile passed in 12.000 seconds at 117.98 mph. Can we call that an 11.9 at 118?
While we are more than satisfied with this result, let me describe some characteristics of the car that will give you a better overall idea of why we came up with the track numbers that we did. First off, the 1.88-second 60-foot time might seem to the avid drag racer as a bit leisurely for a trap speed of nearly 118 mph, and we agree. The primary reason for this comes down to the shortcomings of the stock torque converter. The sucker simply can't be foot-braked very high at the starting line, and we've found it works best to only rev the engine to 1200 rpm before stabbing the throttle when the green lights. Also, the V-2 centrifugal supercharger only begins to really add power over 3400 rpm or so; note from the accompanying dyno graph that output is virtually identical to stock up to that point. Thus, initially off the line you are greeted to a fairly lackluster stock-GTO launch, followed a moment later by a progressive rush as the full 7-8 psi of boost kicks in and presses you into the seatback.
Continuing down the track, the one-two shift keeps you more or less in the meat of the powerband, but then the car suddenly keels over as it hits third. What gives? The answer is that the Two-Three shift drops the engine rpm far enough to take you out of the heart of the powerband, and it takes a couple of seconds before you begin to feel the horses hitting hard again. Once this happens, the acceleration picks up faster and faster until the car crosses the stripe; the driver is keenly aware that had the gear ratio drop between 2 and 3 been not quite so severe, the trap speed would have been well over 120 mph.The Kit:
What the Future Holds
The issue with the GTO's soft launch can easily be remedied by the installation of a torque converter with a higher stall speed. A 2500 or 3000 rpm unit would be ideal, and we'd expect quarter-mile times to drop as much as a half-second. The downside to this, and the reason we are not swapping converters at the moment, is that we are certain the stock driveline would grenade almost immediately: between the rubber-isolated two-piece driveshaft, the notoriously weak halfshafts, and the stock axle stubs, no way would we visit a race track without a trailer waiting in the pits. We are looking to upgrade these drivetrain items before too long, but until then, the sluggish launch stays. As for the fall-on-its-face-in-Third problem our GTO is experiencing, one solution would be to swap out the 3.46 gears for something more aggressive. However, with how hard the GTO pulls to the finish line, it is already not too far from 6000 rpm as it lights the win light, so we don't want to risk hitting the rev limiter. And our 20-mpg-or-so highway mileage (virtually identical to before the Vortech) is abysmal enough as it is.
Keeping with the two-to-three shift issue, an even simpler fix would be to raise the rev limiter and bump up the shift point so that the engine is spinning faster when it hits Third. This could easily be done using our DiabloSport Predator programmer that Vortech provided, but Vortech has advised against raising the rev limiter at this time. Although you'll note from the dyno graph that the power has only just begun leveling off as it hits the stock 6200-rpm rev limit--hinting that good power could still be available at 6500 rpm or more--Vortech chooses to stay with the stock rpm limit on its GTO kit. We're going to stick with its choice for the time being, and the reason can be expressed in one word: reliability. Vortech wants each and every car to be as dependable as possible after installation of one of these kits, and since our particular GTO is a daily driver, we can't agree more. Our current boost level and engine speeds will yield years of carefree driving so long as we keep up with all the required maintenance (more on that below).
But that doesn't mean extra performance is out of the question. Vortech says that if we were to up the rev limit or add any more power, it would be necessary to perform a procedure known as "keying the crank," which is a relatively straightforward process that puts a keyway into the outside surface of the snout of the crankshaft to keep the harmonic damper/crank pulley unit from rotating on it. You see, while stock LS1 crankshafts have their harmonic dampers pressed and bolted on, they are not keyed as in the past. This probably saves GM four cents per car, so this change is understandable (at least as much as killing the F-body was). Keying the crank is a common procedure done on supercharged LS1 engines, where the stock crank experiences added stress thanks to having to drive a supercharger in addition to all of the other engine accessories. Vortech says its efficient compressor design, combined with the minimal pressure drop through the air-to-water-to-air intercooler system, means it takes very little power to drive the supercharger at these boost and power levels, so the stress on the crank is minimal as of now and keying it is not necessary.
Another reason we can't up our rev limit just yet is peculiar to our particular GTO: we are still using the stock fuel pump. Let us explain: As we got our hands on one of the first GTO kits Vortech had put together, we did not receive a replacement fuel pump. Vortech initially offered the kit only for automatic GTOs and found that the stock pump was adequate to handle its needs. But when Vortech put a kit on an M6 car, it found that, for whatever reason, the Goat needed extra fuel beyond what the stock pump could provide. Thus, Vortech now includes in all of its GTO kits a replacement in-tank fuel pump. They sent one to us too, but said we wouldn't gain anything by putting it in, so we haven't bothered as of yet--mainly because the fuel tank must be removed to complete the job, which appears to be a class-A pain in the ass. When the decision is made to embark on further engine mods or increased boost, rest assured: that fuel tank will be coming out lickety-split.
There were very few problems that needed to be addressed after the first few drives of the car, and in GMHTP's tradition of completeness, here they are. First off, we began smelling oil occasionally, most often after we had given the car a hard romp and brought it to rest. It is not uncommon, of course, for high-horsepower cars to build crankcase pressure (due to natural piston ring blow-by) and send it out the dipstick tube or cause the PCV valve to unseat itself, releasing some oil vapor into the air. We began inspecting the engine compartment for clues and initially did not notice anything abnormal. Though in the initial installation we had rerouted a vent tube that the factory had run from the valve cover to the throttle body (and instead routed it upstream of the compressor), I suspected some other vent existed that had not been similarly rerouted. Sure enough, I spotted another vent tube connecting the lifter valley to the intake manifold, just aft of the throttle body. Again, we got one of the first GTO kits out the door, so chock this up to the first version of the kit instruction manual; the error has since been corrected. We got the right PCV valve and put it in--problem solved. The oil smell had apparently been due to the still-existing vent tube, allowing the compressor to pressurize the engine crankcase, pushing oil vapor out the valve cover breather and back upstream of the compressor. This vapor was getting sucked through the compressor while on the throttle, but when we let off and the bypass valve opened, it blew this vapor out the air filter and up to our noses. That, as they say, is that.
The second issue was purely the fault of the installers. When we went to change the oil after a couple thousand miles of driving, we noted that the oil pan skidplate had a good amount of engine oil resting atop it. We feared the worst and thought that maybe the oil drain we had drilled and tapped into the pan was leaking, but fortunately it was bone-dry. It turns out that the leak was coming from the braided feed line fitting above the oil filter block. All it took was a bit more tightening and all was well.
Perhaps the most significant and annoying issue we experienced with the kit was the fact that the aluminum tube running from the outlet of the supercharger to the inlet of the charge cooler contacted the underside of the hood liner. This caused the top surface of the pipe to turn black as the hood liner melted onto it, particularly when the pipe got hot (during full-throttle blasts with warm, not-yet-aftercooled compressed air heating the pipe). The solution to this was to trim the hood liner using a box cutter. Some trial and error was involved to get all the right portions cut, as was some readjusting of the angle of the discharge pipe, since the pipe would then touch the hood itself instead of the liner. Now we have it so that the pipe doesn't touch the hood (maybe just barely) and the appropriate liner parts have been cut away, leaving our pipe nice and clean.
Finally, it has taken some time to get used to some of the acoustics that now emanate from under the GTO's hood. There is more noise in reverse than in other gears, and for some reason the blower sounds like it is varying rpm as one makes turns, but we're quite sure that nothing is awry with the installation and that this is all normal.
Other than these small issues, we have had no problems with the GTO, even after over 2,000 miles of driving. This just goes to show once again how well-engineered this kit is.
After all you've read so far, you're probably thinking that there are no drawbacks whatsoever to a supercharger system, save for the several-thousand-dollar hit to your next MasterCard statement. You are almost 100 percent correct. But just be aware of the following extra care that needs to be taken on a Vortech-supercharged vehicle to help ensure years of reliable Mustang, AMG Mercedes, Porsche, and even entry-level Ferrari ass kicking.First, oil changes must be done more frequently. Most of the readers of this magazine likely use synthetic oil in their cars' engines and probably have gotten used to letting the oil go 5,000 or 7,500 miles before changing it. No longer. Vortech says to change the oil in Vortech-equipped vehicles every 3,000 miles. This ensures the cleanest possible oil lubricating the supercharger gears and bearings. Use the best quality oil filter you can buy, too.Second, forget going 100,000 miles on those platinum spark plugs. More horsepower means spark plugs will be eaten up more quickly. Vortech says you can use the same plugs that come from the factory, but requires them to be changed every 15,000 miles.
Third, let your engine warm up before beating on it. This is good advice for any car, but is even more important with a Vortech under the hood. Make sure the coolant temperature gets to its normal operating point, then wait a few minutes longer so that the oil gets a chance to heat up, too. Also, Vortech says that a car equipped with one of its superchargers can never be cold-started in air temperatures below 25 degrees. This is because of precise, tight clearances within the superchargers. Garage storage or use of an engine-block heater is needed for temperatures below 25 degrees or else you risk "immediate supercharger failure."
Finally, the supercharger oil inlet fitting needs to be cleaned with pressurized air whenever the oil is changed (i.e. every 3,000 miles). To do this, it must be removed at the supercharger and disconnected from the oil feed line. This cleaning procedure is important because the internal screen can become clogged with particles the oil filter missed over time, and because the small orifice at the end of the fitting must stay perfectly clean so as to deliver a precise oil spray pattern onto the supercharger gears.
And of course, always use premium unleaded fuel of at least 91-octane.
One final concern of supercharger buyers that shouldn't go unmentioned is the issue of supercharger lubrication. Most manufacturers use self-contained lubrication systems for their superchargers, requiring no outside oil source. Vortech has taken some criticism over the years for its use of engine oil to lubricate its superchargers. Rather than mince words myself, here's the response straight from Steve Padfield of Vortech Engineering: "[Vortech's] maintenance-free lubrication system uses engine oil that is pre-filtered and injected directly onto the drive gears. We chose this configuration as opposed to a `self-contained' setup because engine oil provides faster warm up, excellent reliability, and superior cooling. The lubrication oil benefits from continuous filtration, being routinely changed along with the engine oil (instead of an additional maintenance action). This system also offers the best opportunity for thermally stable operation. Vortech firmly believes this is the best method to feed and care for a supercharger."
You haven't seen the last of our Vortech-blown '04 GTO, but for the moment, we're off to enjoy some more spirited driving in what is by far the most enjoyable streetcar this author has yet built. Muscle GTOs of the '60s, while they are sweet, just can't compare to the power, handling, and driveability GM and Vortech giveth us now. Friends, at the risk of sounding too sentimental, we truly are living in a golden era of performance.