question on 200tq tuning

[Brett Dikeman]

At 3:07 PM +0100 6/23/04, pronn at rock.com wrote:
>Fellow 200 drivers,  I am looking into a possible stage 2 tune for 
>my '91 200tq20valve.

"stage 2"?  Ie, you have a chip and you want to do more?  If so, 
that's big bucks.  Injectors, MAF, turbo, exhaust manifold, and ECU 
programming to match all that- and yes,they must be done together.

>  There is also a K&N filter installed.

These are lousy and do even less on a turbo car than they do on a 
normally aspirated car.  Filters for the 200q20v cost well under $10 
from the local auto parts store, and yes, just about any brand will 
do fine (I stay away from Fram just on pure principle, however). 
They're pretty easy to change, as well.  By the time you get through 
with the K&N filter, the cleaning stuff, the oil, etc...you'd 
probably have to buy dozens of paper filters before the K&N was more 
cost-effective.

Especially if over-oiled they can cause contamination on the MAF 
sensor, which costs over $300 to replace.  K&N's claims of increased 
filtering via their "it's wet, so it traps more!" has never, to my 
knowledge, been actually proven.

Cone filters are even worse- they often fail to provide smooth enough 
airflow, which is very important for the MAF sensor to work properly. 
Look at the top side of your stock airbox.  See the Venturi horn? 
That's there for a reason.  See the really wide opening in the front, 
with the curved lip?  Ditto!  Audi/Bosch have lots of smart guys 
working for 'em to figure out exactly how to make that airbox flow as 
best it can.  Lastly, cone air filters usually have dramatically less 
surface area, and thus must have very large pores with low filtration.

  K&N's do flow a little better than a paper element since they're 
more open.  This makes them better, purely from a power perspective, 
on highly modified or very well designed normally aspirated engines 
where the intake plumbing itself is less of a restriction than the 
filter, and the airbox size can't be increased because of rules (ie 
racing) or space limitations.  Many race cars run so low # of hours 
and rarely under very dusty conditions, so the lack of filtering 
isn't a huge concern for them...and really serious racers may not run 
a filter other than a really open foam unit, since they may tear down 
the engine on a regular basis.

There's an old rule about aftermarket performance do-dads.  Ask 
yourself, "if _______ is so good, why didn't the original equipment 
manufacturer use it?"  This is very valid, because manufacturers will 
KILL to get some extra "free" horsepower.  So why is it that not a 
single car company on the face of the earth- uses K&Ns from the 
factory?

Answer:

-they cost more; more expensive materials, more complex 
manufacturing, lower volumes, less market competition.
-they are extremely labor intensive to service.  Clean, rinse, dry, 
oil.  As mentioned the filter can be overoiled, causing expensive 
component failure.  it is virtually impossible to mess up a paper 
filter element change.
-they do not filter as well, which means increased failure rates for 
engine internals
-they do not, for most cars, provide any performance increase because 
the rest of the intake system(such as the MAF sensor) are more of a 
problem

Further research shows I'm not quite right- apparently Ford installs 
K&Ns on the "Cobra R" model (which I believe is extremely limited 
production #'s, maybe even at least partially hand-assembled).

>Are there any simple mods I can do at home with standard tools for 
>increased performance? Do H.P. injectors make a big difference

Upsizing injectors without reprogrammed fuel maps will result in 
extreme rich running as the ECU will be using grossly inappropriate 
injector timing values for the airflow it senses.  Larger injectors 
are not necessary unless you plan on doing more than "just a chip". 
Injectors that are too large reduce the metering precision of the 
system because the ECU can only use a subset of the injector's duty 
cycle range.

>, and how do I change out my waste gate spring?

You don't change the wastegate spring; it works fine and is good for 
significant levels of horsepower as-is.  The engine controller is 
very sophisticated with knock detection, charge air temperature, etc- 
this isn't just a purely mechanical, pressure actuated wastegate 
setup; the ECU plays an active role in boost control.

Prost's "Bosch Fuel Injection" is a excellent introduction and 
discussion of everything from early Jetronic CIS systems to the early 
Motronic systems; it covers Motronic theory of operation quite 
nicely.  A local library -might- have it, since it's been out for 
quite some time.  Look for a blue soft-cover book with a photo of a 
MAF sensor with a glowing wire.

Brett
-- 
"They that give up essential liberty to obtain temporary
safety deserve neither liberty nor safety." - Ben Franklin
http://www.users.cloud9.net/~brett/