Wastegate mod.....

[Jay Wallace]

At 08:56 AM 10/14/97 EST, you wrote:
>     Simon, Robert,
>     
>     In my experience, Electronic boost controllers (EBCs) can considerably 
>     improve the boost curve of a car, but my experience revolves around 
>     cars do not have the wastgate directly connected to boost pressure, 
>     but instead have a solenoid in the line controlled by the ECU. Many 
>     Japanese cars have this setup. The boost is controlled by the ECU 
>     outputting a PWM waveform to the solenoid. Most ECUs that have this 
>     setup do not have closed loop control, but instead calculate the pulse 
>     width from the revs and throttle position. This setup means that if 
>     exhaust/induction mods are made, the boost curve can change due to the 
>     control system being open-loop. Also, atmospheric conditions can alter 
>     the boost curve. Also most manufacturers will attempt to make the 
>     power curve of the car come on smoothly for a 'refined feel', which is 
>     not always optimal for the performance enthusiast who wants as much 
>     power as possible at any operating point. The EBC improves the bottom 
>     end boost of such cars, and also provides extremely accurate closed 
>     loop control of an adjustable boost level. I admit that many cars with 
>     an EBC can feel very peaky as torque can come on extremely quickly, 
>     but this feels great, and as long as you stay in boost revs, it is 
>     quite responsive.
>     
Snip...

I have been following this thread with considerable interest. I
have a 93 rx-7 twin turbo that is a wonderful car but, at least in
comparison to a friend's mr-2 supercharged, has less than ideal
throttle response. This is particularly unnerving in corners when
boost suddenly comes on, especially in the wet where traction is
limited. One possible solution would be for a PID boost controller
to incorporate the throttle position as the boost setpoint. For
example, zero boost (atmospheric pressure) would be allowed at one
third  throttle, with increasing boost levels allowed with
increasing throttle position, up to maximum boost at full throttle.
In this way some of the peakyness might be taken away, giving a
more linear throttle response. This is clearly a complication to
the PID controller circuit / code, but you might want to consider
allowing for such a variable setpoint in the initial planning
stages. What do you think: does this idea have any merit?

Jay