1985-1998 [Subscribe to Daily Digest] |
[Profile/Gallery]
, Fri, 13 Oct 2000 18:19:35
Members do not see ads below this line. - Help Keep This Site Online - Signup
this route. Boost controllers disable the boost control system Saab has
engineered into their Trionic ECU.
I would really stay away from the set-up that puts a bleed screw in the MAP
sensor line. That "trick" will result in lean fuel mixtures under high boost
and could result in engine damage
I can help a little describing some functions.
The MAP (Manifold Absolute Pressure) sensor is a pressure-to-voltage converter.
At X psi pressure on it's inlet, it supplies Y volts on it's output.
The output of the MAP sensor is feed to the ECU (engine control unit).
In the ECU the current pressure is compared with the limit pressure (really a voltage level)
programmed in a ROM in the ECU. If the pressure is higher than the set max
pressure, the fuel cut-off is enabled.
The MAP sensor out put is also used to determine the proper mixture when the
motor is under boost. Higher boost requires more fuel to prevent spark knock. Fuel mixture is determined by a bunch of variables, MAP sensor,
inlet air temperature, motor RPM, transmission gear, etc. All these sensors
are used to determine the proper mixture under boost. When the motor is not
on boost, the oxygen sensor is also used to determine the mixture.
As you can see, the MAP sensor is an integral part of the engine management
system. If you put a bleed valve in the MAP sensor you may increase the
boost you will get before fuel cut-off, but you will also be causing the
motor to run lean and a lean mixture will lead to detonation and detonation
will lead to holes in the pistons.
I do not understand how swedish dynamics sells the bleed valves in good conscience.
Both systems use a bleed valve in the wastegate actuator line. One happens
to use it with the APC/BPC valve functioning, the other disables the valve by
plumbing around it.
The system with the BPC valve just bleeds pressure from the actuator hose,
essentially causing the wastegate to open later than the ECU desires. The
effect of this bleed valve is to reduce the gain of the boost control system.
Too much pressure bleed will result in lack of control
The HBC eliminates the APC/BPC valve completely. With the HBC, the ECU does
not have ANY control over boost.
Both controllers can raise boost pressures, but they eliminate the safety
measures that protect the motor from potential damage. If you inadvertantly
filled you tank with 87 octane fuel, after you had set up you boost controllers
on 93 octane, you could be looking at dangerous detonation.
Saab uses the most sophisticated engine control system in production. Installing a bleed valve or a boost controller compromise this system.
If you want more power, the best, safest, and the system that produces the
most gain, is an ECU upgrade from a reputable tuner. Abbott is the more
common one here, but many others exist in Sweden.
Adam, you must get your low boost problem fixed before contemplating any mods.
I have had many "discussions" with Dean on the other BB. He is a very
evangelical proponent of boost controllers, HBC in particular. He seems to
have all the answers. Ultimately the decision is yours.
Is it worth $100 to get 14-15 psi of somewhat questional boost from a HBC,
or spend $900 and get 16-18 psi of safe boost that uses all of the ECU's
control functions.
jj
'95 Abbott insired Aero
, Fri, 13 Oct 2000 18:19:35
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
