The Aftermarket

It amazes me how poorly designed and poorly researched 90% of all aftermarket parts are that I've come accross. For every great company developing good car parts, nine more exist that seem to have no background in engineering. I'm no engineer either- but I'm no idiot- and the flaws in some products are insultingly obvious. What do they take me for?

The most recent embarassment of a product I've come accross was from none other than Subaru Performance Tuning (SPT). SPT is Subaru's own entry into the crowded aftermarket for their own vehicles, and SPT has the trump card of being the only products for the car that will not void any part of a customer's warranty. This implies several things to me, the foremost of which is an assurance that the product does not cause any malicious changes to the car.


However, just a cursury look at the intake reveals several problems:

1. The mass air flow sensor, a very precise instrument used to measure the volume of incoming air into the engine, is placed between two bends in the pipe. The sensor therefore receives a turbulent, uneven flow of air, for which the MAF is not calibrated.
2. The diameter of the intake is smaller than stock, causing air to flow faster through the tube. The mass air flow sensor thus reads higher, causing the engine to think more air is going into the engine than really is. As a result, the car will add too much fuel to the air/fuel mixture.
3. The intake draws in warm air from the engine bay, whereas the stock airbox draws in cold air from outside the hood. Warm air results is less dense with oxygen molecules and therefore contains less energy potential. This results in less power potential.
   
4. The intake uses a cotton filter. The filtering qualities of cotton filters are questionable versus the OE paper unit, however less debatable is the the additional servicing a cotton filter imposes. The oil used in the cotton can dirty the mass air flow sensor, requiring that it be cleaned (a delicate process) every 10,000 miles or so.

Now, I'm just some John Doe on the internet and a far cry away from the engineer types I envision devloping these products. However, these flaws are still pretty obvious to me, and they're flaws that could have been easily (and cheaply) circumvented. If I can see these problems, how can SPT not see them? How did Subaru approve it?

These very questions are what lead many of SPT's customers to disregard their better sense and ignore their doubts. Subaru's stamp of approval implied that all these seemingly obvious flaw were either imaginary or overcome. Besides, SPT claimed a horsepower gain, not a loss.

Cobb Tuning, a rival company well-known for Subaru aftermarket products, echo'd the comments of others and assured the intake would result in power loss and a poorer running engine. Upon request, Cobb tested the SPT intake and released this document showing their results:
http://www.cobbtuning.com/tech/instructions/SPTLegacyGT1.01.pdf

While the document should be taken as propoganda (it is from a rival company, after all), the results were rather expected. Some tests have been since repeated independently by users, adding validity to Cobb's document. In short, every assumed shortcoming of the SPT intake turned out to be valid.

I find it repulsive that aftermarket companies release these poorly designed products, and it's unfortnate that poor engineering can be found even in "official" products. Customers buying the SPT intake over another for the sake of keeping their factory warranty are only going to reduce the lifespan of their engine, even if only by a small amount.

I wish this was an isolated case, but poorly engineered products can be found in all corners of the aftermarket.

Aftermarket brake manufacturers are keen on pushing drilled rotors because they look cool. Drilling a blank rotor only reduces its braking capacity, which defeats the purpose of a brake rotor. Drilling stock-sized rotors is downright dangerous as you cripple braking below stock levels. Unfortunately, drilled rotors make up the vast majority of the aftermarket, and each one claims the (without any data) that drilling the rotor helps braking performance. These claims are wrong.

Aftermarket springs are often designed with a total disregard to load capacity, lowering the car far beyond safe levels on stock shock absorbers. The soft spring rates and reduced suspension travel usually rely on the car's urethane jounce bumpers to carry the extra load of the car. Not only does performance and ride quality suffer, but the sudden changes to spring rate from the car hitting these jounce bumpers makes for very unpredictable handling. Shock absorber life usually deteriorates rapidly. Tein is leading the development of awful springs with their "Style Master" line of springs, and I'll give them credit for at least disclosing the intent of the springs in the product name. Other companies promise better handling, and in most applications, this won't be the case.

Extremely progressive springs, extreme plus-sized wheels and tires, and nearly anything promising better fuel economy (tornado air intake, anyone?) are other automotive no-no's.

Now, I know I've written this article without documenting my latter claims, and I admit this is irresponsible. I think an in-depth discussion of each subject is beyond the scope of this tiny little blog entry. If you don't want to take my word as gospel, Google will find you plenty of information.

Just remember: buyer beware!