How to increase boost levels on a Talon/Eclipse/Laser.

Written by Eric Typpo

Ver. 1.0a   4/11/95


I.  PRELIMINARIES AND WARNINGS

!!!!!

Note!  In 1995, the turbo system seems to have changed significantly
from the 1990-94 turbos.  Not only is the turbo itself different, but
other components in the intake path have changed.  The turbo bypass
valve, in particular, doesn't seem to work well when the boost is
increased past stock levels, leading to premature failure of the turbo
itself.  If you have a car from 1995 on, do not attempt the modifications
below until more data is available.

If you have a 1990-94, take heart.  The mods below have been tried and
tested for over five years now, with no apparent decrease in car
reliability.  However, proceed with caution.  Any damage from modifications
is, of course, your own darn fault. :-)

!!!!!

One advantage of a turbocharged cars is that they can generally be 
modified to produce substantially more horsepower by increasing boost  
over factory levels.  The Diamond Stars respond very well to increases in 
boost, and boost can be increased at a cost of $0!  However, there are 
some things to keep in mind:

1.  You *ABSOLUTELY* must get an aftermarket boost gauge before fiddling 
with boost levels.  The factory gauge does not really measure boost, and 
is not accurate beyond stock boost levels.  HKS sells a very nice gauge 
which is fairly expensive, and J.C. Whitney sells one (actually several) 
for less that several people on the list have had good results with.  
Running excessively high boost levels will cause detonation which can 
create the need for very expensive engine repairs.  (Also highly
recommended is an EGT - see the end of #3).

2.  Although you don't absolutely have to, freeing up intake and exhaust 
restrictions will give you better results once you increase boost levels.  
Both are fairly restrictive to begin with, and they become more of a problem 
when boost levels are increased.  Also, reducing exhaust restriction will 
decrease combustion temperatures, which is a desirable thing, and 
backpressure from the factory exhaust may limit the amount of boost that 
you are able to get.  There is a FAQ on reducing intake restrictions, and 
there are many exhaust options available depending on your budget and 
your taste in decibel levels.  

3.  The key to not damaging your engine when you increase boost is 
maintaining a proper fuel/air mixture.  In particular, you want the 
mixture to stay fairly rich to keep combustion temperatures from getting 
too high and causing detonation.  However, what you are doing by 
increasing boost levels is introducing more air into the engine, therefore 
creating the possibility of a lean mixture.  The stock fuel system can 
provide additional fuel and maintain acceptable f/a ratios to a point, 
but it runs out of capacity somewhere in the ballpark of 15 psi.  
However, it is still a good idea to check to make sure that your car is 
maintaining adequate f/a ratios if you increase boost at all.  

There are two ways to monitor fuel/air (f/a) ratios:  First, the function of 
the oxygen sensor is to monitor f/a ratios for the ECU.  It produces voltage 
in proportion to the a/f ratio.  High readings (~.9v) 
indicate a mixture which is conducive to long engine life under wide open 
throttle (WOT).  The reading should go to ~.9 and stay there as rpms 
increase.  When you reach the limits of the stock fuel system, the voltage 
will start decreasing as rpms increase.  
Lower voltage = leaner a/f ratio = possible detonation, so 
back off the boost if this occurs.  On the Diamond Stars, the factory 
thoughtfully provided a wire which can be used to monitor O2 sensor 
voltage in the dash above the passenger's footwell, taped to the main 
wiring harness that goes through the firewall, so you can connect a 
voltmeter to it, and get a reading.  The second, and IMHO, better way to 
determine whether your car is running rich enough is to get an exhaust 
temperature gauge.  This monitors combustion temperatures directly and 
can be obtained from many sources.  Westach makes one for about $80 which 
only requires drilling a hole in the downpipe, rather than the O2 sensor 
housing, like the one HKS sells.

4.  Many people have increased boost to the 15-16 psi range, and not had 
problems, but you *are* increasing stress on the engine, and any problems 
with the fuel system (i.e. plugged injector, clogged fuel filter) will be 
more likely to cause engine damage, so you are doing this at your own 
risk.  Make sure your fuel system is in tip-top shape before attempting
modifications.  Also, premium fuel is mandatory rather than optional at this 
point.  Beyond 15-16 psi, modifications to the factory fuel system such 
as additional fuel pressure and upgraded fuel pumps become necessary to 
avoid lean f/a ratios  (try the fuel pump first).  If your car starts bucking
at WOT with high boost levels, you have found the fuel cut programmed into the
ECU which is designed to protect the engine (but don't rely on it) from too
much boost.  Reduce your boost level to eliminate it.  The fuel cut is more
likely to occur in cold weather due to greater air density.  It may occur at
boost levels as low as 14 psi on cold days. 


Before getting into the ways of increasing boost, it is helpful to 
understand how the boost control system works.  On the Diamond Stars, a 
pneumatically activated wastegate controls boost.  The wastegate opens a 
passage for exhaust gases to bypass the turbo when a preset boost limit 
is reached, which limits the amount of boost that can be produced.  A hose 
is attached to a nipple on the outlet pipe that is bolted to the compressor 
side of the turbo which provides the air pressure "signal" that opens and 
closes the wastegate.  All methods of increasing boost on these cars use some 
means of reducing the air pressure that the wastegate "sees" through this hose 
so that it stays closed at boost levels where it would normally open.  From 
the factory, the cars are already designed to bleed some of the pressure off 
the wastegate hose.  The black plastic thing on top of the air cleaner 
cannister with two vacuum hoses running to/from it is a solenoid designed to 
bleed off some pressure off the wastegate hose if no detonation is present, 
thereby increasing boost by a few psi. If detonation is present, the solenoid 
closes, pressure to the wastegate increases, and boost is reduced.


II.  INCREASING YOUR BOOST

Several options exist to increase boost levels:  

1.  HKS makes a product called the Electronic Valve Controller (EVC) 
which is a fairly sophisticated means of controlling boost.  An 
electronically controlled valve precisely maintains the preset boost 
level, regardless of temperature.  It also controllable from inside the 
car, so you can change boost levels on the fly.  However, it is fairly 
expensive (~$700), and virtually identical results can be obtained more 
cheaply (under $20, see #3).

2.  Superchips makes a Graphic Boost Controller which allows variable 
boost levels at different rpms.  The controller looks like a graphic 
equalizer, and allows the user to set boost levels at 500 rpms intervals.  
The advantage of this controller is that it allows you to 
run higher boost levels at lower rpms, where the stock fuel system can 
maintain acceptable f/a mixtures, and then taper off at higher rpms where 
the fuel system can't, so you have the ability to make more power through 
the midrange than with the other methods of increasing boost.  It is also 
cockpit adjustable and costs $350.

3.  You can also use a bleeder valve.  Bleeder valves are fairly cheap 
pieces of equipment.  They are available from HKS and elsewhere for 
$80-$100, but all you really need is some type of valve that allows you to 
control airflow through a vacuum hose.  They can be used in place of or 
in addition to the boost solenoid on top of the air cleaner.  Their 
function is to regulate the amount of air that is bled off from the 
wastegate hose so that boost is limited to a safe level.  They may require 
some adjustment with changes in temperature, but by keeping the vacuum
hoses to/from the valve fairly short, the problem is minor at most.  
These valves can be cockpit mounted, but they tend to be noisy and not 
work as well, so underhood mounting is preferable.

4.  Another option to increase boost for free is to modify the boost 
solenoid.  However, doing so eliminates your ability to go back to a 
"factory" configuration, and there is some potential to break a $52 part, 
so proceed at your own risk.  What you are trying to accomplish is to 
allow the solenoid to bleed off more air from the wastegate than it does 
in stock form.  Several modifications will allow this to occur.  First, 
inside the "intake" nipple (the one facing the firewall - see diagram 
below) there is a plug with a small hole which reduces the 
inside diameter of the nipple.  This can be removed by "hooking" it out with 
a bent paper clip, or by getting a drill bit or small screw to "bite" into it, 
and pulling it out.  Next, the nipples can be drilled out to a slightly larger 
inside diameter.  The diameters seem to vary somewhat, so bit sizes vary,  
but don't try to increase them too much.  Also, be careful that 
you do not drill too deeply.  Mark the drill bit with tape so that 
you do not go into the solenoid body.  Finally, replace the factory 
hoses with some 5/32" vacuum hose.  This usually gives about 14-15 psi of 
boost with a completely factory appearance.  This method is also somewhat 
safer than the preceding methods because the ECU still has the ability to 
decrease boost if detonation occurs, unlike methods which remove the 
solenoid.  However, keep in mind that the ECU may take some time before it
decreases boost, so you can still damage your engine if you aren't careful.


  |  "Intake" nipple - to wastegate hose.  Plug is inside this nipple.
  |
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|          |_____   "Exhaust" nipple - to air cannister
|          |
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