To say that the Pirelli World Challenge series is growing would be a massive understatement. They have more manufacturer interest than ever before as well as a few teams who would usually be running United SportsCar who've joined in the fun. How awesome is the field this year? Look at this test day.

Everything from ubiquitous sportscars like the Porsche 911 GT3 Cup and the Nissan GT-R GT3 to exotic machinery like the Bentley Continental GT3 and the Dodge Viper GT3-R to American specials like the Cadillac ATS-V.R GT3 and the Acura TLX-GT will be at this race.

Many of the cars testing this week were made to FIA GT3 specifications. PWC's embracing of the GT3 spec seems to be successful so far. Unless you're building a GT3 racer from the ground up like Cadillac, you can pick up a ready-made race car from a manufacturer and have at it in World Challenge. With TUDOR United SportsCar adopting the GT3 spec for its GT Daytona class next year, several endurance teams are fielding a car in World Challenge this year to get used to the GT3s.

. Drool. Drool. Droooooool.

In some cases, such as the Flying Lizard/K-Pax McLarens, World Challenge will be the opportunity to see those cars raced in America.

Want to see the new McLaren GT3 race car racing in the United States? You're in luck. K-Pax Racing…

I can't wait to see these two cars in action.

Although this test day that was mostly GT cars, one of the best parts about World Challenge are the Touring Car classes: TC, TCA and TCB. Ever wanted to see cars that race wheel-to-wheel? You'll see everything from race-prepped Volkswagen Jettas to Mazda2s show up. The racing is as close as the cars are mundane, and everything about it is wonderful. Kia Forte Koups, Nissan Altimas, and for the really fancy set, Porsche Caymans plan to race in the TC classes this year. TCB (often referred to as "B-Spec") is some of the closest racing I've ever seen in person. B-Spec is the class for all the tiny peanut cars like the Ford Focus and the Mini Cooper, and they're fairly evenly matched.

A new class for the year is GT Cup, which is all Porsche 911 GT3 Cup cars. This is but one of ten entries in the new class, which includes everyone from Texan Alec Udell to reigning Porsche GT3 Cup Challenge USA champion Colin Thompson. Here's Victor Gomez's car. (I need one.)

Gomez's beautiful blue camo Porsche was with the DragonSpeed team, who will also campaign several Mercedes-Benz SLS AMG GT3s.

Eric Lux's DragonSpeed entry was in Mercedes' traditional silver, and it looks classy in every single way, almost like a really aggressive road car.

Few things in this world are more impressive than a garage full of gullwings with their doors open.

The Black Swan Racing SLS of Timothy Pappas is perhaps my favorite of them all: it's chrome. Ridiculous, wonderful chrome and shiny teal.

Given what I found outside, the teal may be for Project Mu's brakes.

Everything must be labeled on a race car, including spare brake rotors that are beyond done.

One thing you'll notice about the World Challenge cars in the GT classes is how far back the engine is in the engine bay compared to most street cars. It's something I noticed with the outgoing Cadillac CTS-V.R and it's a principle that rings true today: move that giant lump of weight more towards the middle.

Another interesting item: every little piece on many cars has a sticker. Canards, splitters, all of it.

One advantage to the gullwing door: it certainly makes it look like it's easy to hop in and out of. That may matter less in a sprint race format like World Challenge, but it's certainly awesome when you're done with a race and you're tired.

Now these are door struts.

Black Swan Racing SLS GT3 FTW

The SLS sounds as good as it looks, even as it was put away in its trailer.

Some of the Caddy faithful may be foaming at the mouth at my assertion that the ATS-V.R is an "American special." Well, it is for 2015. There's only two running this year, and both are in World Challenge.

The eventual plan is to open the ATS-V.R to customers, just like all the other GT3 cars. However, according to , Cadillac wants to focus on homologation and development of the car this year instead of getting it immediately out to customers.

However, it's homologation that the Pratt & Miller-backed Cadillac team is rumored to be still finalizing. According to a member of another team, the last list of GT3 cars released showed the ATS-V.R with no homologation number next to it. So, for now, for multiple reasons, it remains an American PWC-only special—and not to mention the car to beat.

Given how successful the previous CTS-V.R was in World Challenge, all eyes were on what Cadillac was up to: what are they doing with the car? What kind of laptimes are they running?

The older GT3-spec cars are somewhat of a known quantity, but Cadillac? Not this year, at least not yet.

Cadillac wasn't the only American name at the tests. These lightning quick Camaros from Blackdog Speed Shop are back for yet another year in the GTS class.

And of course, there were some Vipers, courtesy of Lone Star Racing.

They currently only have one GTA entry on the list, but the team was testing out a second car this week.

So much of this car's bodywork was carbon fiber.

You could see the weave reflect through the wrap around it.

This is a car made of scoops, vents and voluptuous curves.

NACA duct fans, rejoice.

I could spend hours staring at all the features of the Viper, but there are several other cars worth noting at the practice day.

The Audi R8 LMS Ultra is gorgeous, as always, complete with a carbon fiber block-off plate where the street car's fog lamps should go.

The Turner Motorsports BMW Z4 GT3 of Bret Curtis is clearly a fan of the local cusine.

Its sister car looked just as wonderful, even without the flaming tailpipes.

Bill Ziegler's car looked particularly mean in this silver and black livery.

Turner is allowed to run the GT3 aero as it was originally designed in World Challenge, which they can't do this year in their class in United SportsCar. Will Turner be as dominant here with their pair of Z4 GT3s as they have in TUSC, though? We'll find out in a week and a half, I suppose.

Here's a huge torque wrench for center-lock wheels.

The Aston Martin GT3 V12 (yes, V12!) of LG Motorsports had about as much carbon fiber as the Viper.

The hood alone was all carbon fiber, and all wonderful.

With that much carbon, a side-exit exhaust and a giant V12, this car could be one of the rowdiest cars in the race.

GT3 wings are about as good as they get on a GT car. Big, wide and fabulous.

Surprisingly, the big V12 Aston could also win the award for "cutest canards." They're tiny, but if you don't need bigger aerodynamic add-ons to go fast, why bother carrying around the extra weight?

It's clear GT3 cars are also made for endurance racing, though. I would gladly sit in here all day long.

The LG Aston Martin wasn't the only car that looked like a new delivery, all in white. Alec Udell's GMG Porsche looked shiny and perfect in naked-Cup-car white.

There's one other pair of cars you're unlikely to see anywhere else that were at this test: the two Acura TLX-GTs of RealTime Racing.

If you expected these to be anything like your mom's Acura, think again. It may be based off of a regular TLX, but it's been extensively modified beyond that: the engine's been moved back, big carbon fiber fender flares have been added to the body, easily removed body pieces like doors and hoods have been lightened, and of course, it has all the wonderful aero that would put your average Honda Kid to shame.

It even shares a center-of-wheel panel with Honda's P2 prototype racers. The center LCD panel doesn't work with this car, but many of the other switches and knobs (such as the "pass" button that flashes the car's lights) work just as they should.

Listen to it. This car burbles, pops and hauls the mail like no Acura I've ever seen on public roads.

The neon canards speak to my inner ricer on a level that was repressed sometime around when underglow became uncool. They've managed to make a functional item bright and wonderful, standing out from all the über-serious applications of naked carbon fiber everything.

Don't get me wrong. My inner ricer craves carbon fiber everything like normal humans crave Doritos. It's just that neon is a nice change. Here are the lightweight doors (albeit wrapped, but the pattern of the reflection gives it away) to appease the Deities of All Things Carbon.

Driver was a bit preoccupied with the bunny shooting Alien-style out of his gut as well, however, he seemed happy with the car.

Both he and Peter Cunningham looked fast in the most surprising Acuras ever, even if I didn't hear any laptimes for them.

It was so unusually cold for the test day that the morning was interrupted by sleet, and the afternoon sessions had trouble getting heat in the slicks. So, they stayed out on wet tires and threw down some very quick laps. Sure, the tread looked more like it had alligator leather skin than a tire pattern once the day was done, but they did their job.

Eversley was added as a second driver for the RealTime Acura team, and the fact that he has factory backing from Honda means that yes, manufacturers are taking a good, long look at Pirelli World Challenge this year. Given its growing popularity, I wouldn't be surprised to see more factory drivers in this series next year at all.

So, if you've ever bemoaned the lack of relevance that race cars have to the funny conveyances you see on normal, public streets, World Challenge is your dream series. Not only is a vast cross-section of cars you'd see in real life going to race that weekend, but a great number of them are the kind of cars where you'd drool all over yourself if you saw one in a parking lot.

Pirelli World Challenge's season opener runs on March 6-8 at Circuit of the Americas. The GT races will be televised on March 14 at 11:00 AM EST and TC races will be on March 18 at 8:00 PM EST, both on CBS Sports Network.