Performance
Most of the time, a $20 imitation part will pale in comparison to its $100 real counterpart, offering little to no gain for the sacrificed Jefferson. From exhaust systems to intercoolers, the counterfeit world seemingly has performance on lockdown. But, more often than not, these parts are a waste of money and a headache in the waiting. Intake pipes often don't fit correctly and unproven intercooler designs feature huge pressure drops and poor thermal capacity. Like a bad photocopy, design details get lost along the way during the copying process, ruining your power-to-dollar-return ratio.
 It really does look like a...  It really does look like a Mugen twin-loop muffler, huh? Ok, not really. Rust has already begun to form around every weld on the muffler's body. These non-stainless welds will quickly disintegrate and fall apart, leaving you with a leaky, broken muffler. |  On the outside, the two adjustable...  On the outside, the two adjustable GReddy Type-RS blow-off valves look the same, but inside, they are vastly different. The difference in diaphragm seal design and construction is obvious. The fake valve's seal is as thin and fragile as it looks, and has begun to rip already. |  The two K&N air filters may...  The two K&N air filters may look the same, but only the left one is washable, holds up to high boost levels and has been proven to filter out dirt effectively. |
Exhaust systems from GReddy, HKS, Injen and A'PEXi are dyno-tested before release, ensuring that a satisfactory power gain will be had. Fake parts have no testing carried out on them, and the money pirate who manufactures them could care less about how much power you're expecting to make. The buzzing leaf blower tone and vibrating interior trim might lead you to believe that you're pulling 10-second slips out of your ass, but don't be surprised when you're left with just 200dB and 85 wheel hp.
Proper Fitment
The Spooned Sports box arrives in the mail and you tear it open with an excited frenzy. The cat-back looks shiny enough and a seven-inch slash cut tip means lots of power, right? Once your friend shows up and jumps out of his Alty, you're ready to go. The car's up on stands, the stock exhaust is in a dumpster and then you hit a wall. There are no exhaust hangers on the muffler, the piping is too short and the canister is too large to fit. Uh oh, it's knock-off headache time.
Making a part that fits seems easy enough, but it's one of the top problems with fake parts. From direct-fit Stoptech brake lines to Edelbrock headers and Magnaflow exhausts, real manufacturers take the time to ensure that parts fit well and are easy to install. We've seen B-series headers that hang too low, "OE-fit" WRX intercoolers that don't line up on the stock mounting brackets and intake pipes that aren't mounted to anything at all.
 Beware of using cheap carbon-fiber...  Beware of using cheap carbon-fiber products. The poor clear coat will fade and dull in a short period of time, making your hood look old and yellow. |  Direct fit headlamp bulbs...  Direct fit headlamp bulbs promise HID quality light by coating the bulbs in a blue tint, which actually reduces the overall light output. Our headlamps suffered some melting damage from these 100/90W bulbs; the stock bulb is rated at 60/55W. Stick with a reputable bulb brand, such as PIAA or Sun Automobile. |  The inside of the fake muffler...  The inside of the fake muffler is no better. There is minimal steel wool wrapped around the pipes to protect the fiberglass packing. This muffler will burn out its sound absorption material quickly, going from loud to absolutely deafening. |
Body parts are perhaps the worst of the bunch. Because body kits and hoods don't really have any moving parts or mechanical function, the only thing that matters is if they look good and fit well. Well, zero out of two ain't bad.
Body parts from companies such as Ings+1, Spoon Sports, C-West and Chargespeed are designed and tested for fitment and aerodynamic function. Knock-off parts are usually made on the cheap, with hundreds of bumpers coming out of one mold. This spells trouble for proper fitment and installation. Expect your body shop to charge you extra for the labor involved, such as molding and filling the gaps in your body panels. That is, if the cheap fiberglass construction doesn't shatter apart on you first.
If you're familiar with fabrication and, how do we put this, unique installation ideas, then pickup the cheapest parts you can find. But to us, drilling and tapping multiple holes to install a bumper doesn't sound like much fun at all.