Factory vs aftermarket (Part2)

[Tomchou at aol.com]

>someone building a street engine.  There are numerous tradeoffs 
>between maximum horsepower, maximum torque, and drivability.  One 
>thing we must understand in all this is that GM is forced to build an 
>engine that meet CAFE (Corporate Average Fuel Economy), emission 
>controls, smooth idle, low to mid-range torque, and easy cruising at 
>(in '86) 55 mph.  If the end users concerns lean toward one or more of 
>these criteria, there are aftermarket products that will satisfy their 

This is somewhat true.  There are some aftermarket items that do work well
when they target some compromise in the factory design; we are forced to make
many compromises for the reasons you state.  Most effective changes are the
simple and logical ones, such as less restrictive exhausts (drive by noise
level requirements force certain compromises) and less restrictive intake
systems (again, noise levels are a concern.), or issues such as shift points
and torque management to make transmissions and such survive the 100K mile
durability cycle as warrenty costs are a major concern.  

However, the problem is that most aftermarket don't understand all the
ramifications of changes they make.  For instance, MAFs are particularly
sensitive to turbulance, and the change to an open air element or ram air
(besides the hazards of water intrusion) could alter it's calibration.  Even
if these things are understood, the aftermarket doesn't have the resources to
correctly compensate for many things they do.  This results in at best,
slight irregularities in driveability, and most people that are into
modifications probably overlook this issue, as "race cars" are supposed to
drive rough.

>needs.  To state that these parts are fraudulent or that the people 
>who sell them are liars is irresponsible and/or stupid..

Unfortunately, I've found this to be true more often than not.  Many have
really good intentions, but just don't have enough understanding of the
issues and physical principles.  

>While it is true that the requirements of a particular engine may 
>vary, there are some parts that will increase horsepower and torque, 
>but were not placed on the original engine purely due to 
>economics...Headers, dual exhaust (with dual catalytic converters), 
>high flow air filters, high flow Mass Air Flow sensors, roller 
>lifters, and throttle body air foils are notable among these.  Even 
>the calpak can be remapped for improved performances if done so to 
>accomodate a particular engine and driving conditions.  These engines 
>(from the factory) are made for mass production.  Plainly and simply, 
>they are designed so that the lowest common denominator is met.

Again, this is partially true, but not completely.  This is what every
aftermarket vendor would love for everyone to believe, but don't buy into it
hook, line and sinker!  I'm not flaming the originator of this post at all,
so please don't take it personally!  I'm just expressing my opinion, and this
post happened to be the one that opened the issues!

I know very well there are many compromises the OEM makes, but I've yet to
see an aftermarket company discover and optimize most *true* design
compromises despite their hype to this effect!  The beauty of this particular
list is that everyone is more or less from a technical background, and are
able to talk intelligently about these things.  Many lists such as the
general F body list (just picking on it - I stopped subscribing after too
many "my car is faster than yours") do buy into the aftermarket's advertising
wholeheartedly, but the folks on this list have the knowledge to really
evaluate the validity of vendor's claims.

Tom Chou - Tomchou at aol.com