The limits never used to be this high. There was a day when weight transfer was something you could actually use on a back road to delicately place the rear of the car into a controlled slide, lining yourself up for the next sweeper. Blip the throttle just right to match the revs and fire out, before balancing on the brakes at the end of a short but straight strip of asphalt--just the right poundage on the middle pedal to avoid lockup and ensuing disaster. You couldn't wipe the grin off your face, and it was all happening at 30 mph.

Nowadays pretty much anything on the showroom floor equipped with modern rubber and the "sport package" will walk away from those hardcore sports cars of yesteryear without breaking a sweat. But while cars are becoming unquestionably more capable, are they getting any more fun? Is point-to-point competence all we're chasing?

Too many of us have become so lost in the quest for ultimate speed that we've begun to hear the words "race spec" to mean "the best," and the result is entirely too many roadgoing cars in which fun factor has been traded for outright pace. Or worse, for an overly difficult machine that's no faster on public roads than it was from the factory. Bottom line--a street car just ain't a racecar.

The only thing simple about a racecar is its end goal: setting the fastest lap time possible while being durable enough to last for hours of racing at a time. Street-driven cars, on the other hand, have decidedly more complex mission statements. While point-to-point rapidity is certainly not a bad thing, it shouldn't be a forefront concern. There are a number of fine lines a street car must straddle, while a racecar can simply poop all over them. These fine lines reflect important balances like comfort vs. stiffness, or horsepower vs. noise, but the most important difference is that in a street car, we must deliberately tune in "fun."

We decided to step in and play Mythbusters before the madness we've been witnessing on city streets gets too far out of control. To keep us all ahead of the curve, we went to Dublin, Va., to meet with James Clay, owner of BimmerWorld and the illustrious baby blue BMW 325i racecars you've seen competing in (and winning) the Speed World Challenge Touring Car Championship. As owner of the BimmerWorld performance store, he caters to customers looking to tweak their street-driven cars, and as the star driver of the BimmerWorld race team, he knows which parts go into a racecar and nowhere else.

"When I was in school, I drove a stripped-out, caged E30 M3 with a track suspension," Clay says. "As I've gotten older, I decided I climb out of racecars and race seats often enough at the track that it stops being fun every day. Likewise, whether you realize it or not, as you add harshness with each new race part, there's a building irritation factor that translates to you just not wanting to drive the car as much. Not everyone has the space, money, or time for a track car and a street car, so being honest with yourself to hit your personal balance will result in a car that can fill both needs to your satisfaction."

The racecar
While we everyday rubes are stuck wasting time in dealerships, bargaining with the seedy types that occupy them, the guys at BimmerWorld purchase the raw chassis (body-in-white) directly from BMW. Rather than having to buy the whole car and discard 90 percent, BimmerWorld starts with just the chassis, complete with doors, hood and trunk. The hood and trunk are promptly stripped off and sent away to be used making molds for lightweight carbon-fiber copies. The chassis is fitted with a number of custom structural reinforcements, which are proprietary and thus quite secret, as well as a rollcage. As you'd see from a quick look at the shock towers, this isn't the same kind of cage you'll be getting at your local fabricator. Though technically "just" an eight-point setup, the door bars and the sheer amount of bracing differentiate this cage from the kind you see on open-track days.

The coolest bits on the BimmerWorld car are trade secrets, so we can't show them in pictures. But you'd be a fool to guess that the 2.5-liter inline-six underhood is stock. Built by Sunbelt, it makes upward of 290 hp and has a very narrow range.

"Our racecars idle at 2000 rpm and they live between 6000 and 8300 on the track," says Clay. "That's where they make power. Big cams and a wide-open exhaust work great on track cars and make good high-end power, but if you want your street car to come off the line strong, this setup will hurt your low-end power and you won't be happy with your investment. This definitely applies in choosing turbo sizes--decide what rpm range you'll be running, and remember a big horsepower number is pretty meaningless in real life."

You wouldn't want a race engine underhood anyway. This one is dry-sumped, with a sleeved block, custom pistons, rods, camshafts, lifters and springs, and it needs a rebuild after every 25 hours of operation--if nothing goes wrong. The incredible Ducati-like throttle blips are the result of ridiculously light rotating mass, primarily the flywheel and clutch assembly. You'll never replicate it on the road. Clay says that the most common misapplications of race parts are the clutch and flywheel. "The 4.5-inch twin-disc clutches on our racecars allow the engines to rev incredibly quickly and sound cool, but new clutch disc thickness is 0.106-inch and worn out is 0.095. And if you try to slip the clutch to start the car smoothly, you'll be through that material in a matter of days."

Much of the bad-ass suspension present on the BimmerWorld racecar, like the Moton four-way adjustable Clubsport spring-and-damper assemblies, is designed to work with a racecar chassis. That is, your street car has enough chassis flex that it's often tough to tell the difference between a good suspension and an extremely high-end variant, even in lap times. Feel free to try and make your chassis this stiff, though--BimmerWorld estimates about 450 hours of metal work and fabrication per car, and about 200 more building the subassemblies and putting everything back together. Even if you've pulled it off--"Race parts are meant to be strong and durable, but not always to have a long lifespan," Clay says. "We typically spend about 10 hours per car inspecting and replacing parts after each race weekend." That's after three hours of running.

It's an easy mistake to make. After all, the fastest variant of your car is invariably a racecar. Since you want your car to go as fast as possible, common sense dictates emulation. But the fact is that the parts that make cars go fast on the track aren't the same as those required to make your car fast on the street. And more importantly, as tough as race parts are, they're designed to stand up to a certain type of rigorous treatment--the kind that doesn't involve potholes, rain and snow, and soccer moms.

In some cases, race parts do work on street cars, but as Clay points out, the benefit is usually not worth the cost. Take the giant Performance Friction brake setup on the BimmerWorld 325. Just about any street car can benefit from four-piston calipers all around and floating rotors up front, but it's the brakes' ability to radiate the massive amounts of heat generated throughout the course of a race that makes them really worth the money. And as with the tires, you're not going to want to use racing brake pads on the street, because they'd simply never reach operating temperature.

According to Clay, the 2008-spec BimmerWorld cars cost about $240,000 to build, and there are now 14 people on the team, which campaigns three cars at around a million bucks a season. In a given season, the team can paint and replace as many as 30 sets of fenders. Typical damage costs range between $30,000 and $40,000, but are sometimes much higher. But the cost is finally paying off--Bimmerworld had its first World Challenge win at Road America just last year.

So before you find yourself with an empty wallet, sitting in traffic, and attempting to slip that three-puck race clutch without kicking and bucking like a rodeo bull, realize that you spend a hell of a lot more time on the street than you do on the track. And you don't have to wait until you send a race shock flying through its shock tower to admit to yourself that you've been a bit... ignorant when hooking up your ride.

Heim-joint suspension components
Prepare to shake those fake "M" badges right off the trunk lid. Heim joints work great on racecars for two simple reasons-- there's no consideration for noise, vibration and harshness, all of which are extreme, and they can be replaced every 10,000 miles on a racing budget.

Carbon body parts
Carbon-fiber body parts for street aren't usually the dry carbon weave you'll find on racecars. They're usually wet carbon, and typically consist of a layer or two of weave over a fiberglass body. In addition to not being particularly strong, they're not particularly light. Not to mention you'll be replacing your carefully designed crumple-zone hood with a sliding decapitator. Your door beams designed to protect you from side impacts, but you'll need to remove those to install carbon-fiber doors, and since you shouldn't have a rollcage (see "Rollcage"), you're now a sitting duck. Finally, these parts don't fit well, and they allow enough road noise into the cabin that you won't be able to hear yourself think.

The tiny 2.5-liter engine sitting in the bay of this E90 rips out an astonishing 290+ hp at more than 8300 rpm, but tight tolerances required to create this kind of oomph mean a rebuild every 25 hours at $10,000 each. But the real kicker is the amount of tuning required to make it run right, not to mention the custom wiring and the fully programmable $13,000 MOTEC M800 Pro and MOTEC ADL-2 datalogging system.

Steering wheel/seats
That sweet Toora steering wheel definitely adds to the driving experience. Just one thing: It comes at the price of your airbags. The Racetech seats are top-notch for racing, hence the name, but they check in at the cost of comfort, and worse yet, your blind spots, which probably won't pay off on the highway.

Xtrac sequential six-speed. This is as fast as you're going to get if you still want to move your right arm. And if you thought those carbon-fiber doors were making things noisy in the cockpit...

Side-exit exhaust
Actually illegal in most states, a side-exit exhaust (located on the opposite side in this case) is a great way to get rid of that unwanted leg hair and exfoliate your skin. If you're a good fabricator you can build a relatively quiet system, but where's the fun in that?

You'd love the added stiffness, but unless you plan on wearing a helmet every day, putting a rollcage in a street car is a fool's gambit. One good knock in traffic could send your skull into a bar and--poof!--you're a goner.

Rear spoiler
As we all know, downforce plays a critical role in keeping a racecar planted in high-speed corners, and it works great in this application because of the heavy-duty spring rates. Since there's no way you can run racing spring rates on the street, the massive downforce created by a wing like this would serve largely to push the back of your car into the asphalt. But no worries; you won't be cornering fast enough to notice a difference anyway.

Tires make the single biggest difference in the handling department. But while it's perfectly reasonable for the BimmerWorld 325 to polish off three sets of sticky Toyo R888 rubber per weekend (at $800 a set), your street car will need to compromise, like with a set of Michelin Pilot Sport 2s, which have more than twice the treadwear. You won't have quite the same ultimate grip, but street driving is about having fun, not setting lap times. Incidentally, race tires can quickly overwhelm even the best street suspension setup anyway.

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By James Tate
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