You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
How is boost limited in 1st and 2nd on these cars?
- Thread starter robin2660
- Start date
Like the title says.
ECU?
It is the torque that is limited, which may affect the boost pressure.
In 2nd gear, it is possible to see full boost (~15.6 PSI).
It is the torque that is limited, which may affect the boost pressure.
In 2nd gear, it is possible to see full boost (~15.6 PSI).
I was reading somewhere (can't find it now) how there are multiple inputs such as torque, wheel, and others that the ECU uses to decide how to limit boost, I think.
I'd like to understand this more.
oaklandopen
Member
the way i figured it was that the electronic switches in the gear selection was limiting the boost (the ECU knows when the shift knob is physically in 1st and 2nd gear), and that all other inputs were for the TCS and DSC (like throttle input, steering angle, accellerometer, etc)
wonder if full boost can be achieved in reverse
wonder if full boost can be achieved in reverse
5-4-fighting
Member
Is it possible that the Cobb AP can remove the torque limiter?
the way i figured it was that the electronic switches in the gear selection was limiting the boost (the ECU knows when the shift knob is physically in 1st and 2nd gear), and that all other inputs were for the TCS and DSC (like throttle input, steering angle, accellerometer, etc)
wonder if full boost can be achieved in reverse
The switches on the transmission are for neutral and reverse (for the reverse lights).
The ECU knows vehicle speed and engine RPM and thus it "knows" what gear you are in.
The ECU will keep the wastegate solenoid valve closed to minimize boost pressure. On a stock MS3, this would result in a boost pressure of ~10 PSI.
Exhaust modifications such as a "test pipe" and especially a downpipe will raise the minimum boost by at least 2~4 PSI.
So, solenoid closed = wastegate open (presuming an open wastegate bleeds exhaust)?
phantom6294
Member
So, solenoid closed = wastegate open (presuming an open wastegate bleeds exhaust)?
Errr.... robin2660, no. The wastegate (the actual wastegate) is closed (by closed meaning all exhaust flows through the turbine) until one of two conditions occur 1) enough boost pressure is applied to the wastegate actuator (WGA) to overcome the pressure of the spring tension in the WGA or 2) the exhaust pressure inside the turbine housing is high enough to force open the wastegate.
As I understand it, the MS3 has about a ~10 lb WGA spring -- which means once 10 PSI of boost is being created and 'pushing' on the WGA spring, the wastegate begins to open. As such, 10 PSI is the 'mechanical boost' created by the turbo. Thus, until said boost level is reached, the wastegate remains closed. The ECU can bleed boost away from the WGA via the wastegate solenoid thus allowing the turbo to make more boost than would otherwise be made. For example, in a very simplistic view, if the ECU wants 15 PSI, it would bleed off 5 PSI away from the WGA (15 PSI - 5 PSI = 10 PSI to open wastegate and prevent more boost from being created). So, do not confuse the wastegate, the wastegate actuator, and the wastegate solenoid.
If you datalog, you should also know the Wastegate Duty Cycle (WGDC) PID refers to the duty cycle applied to the wastegate solenoid. So, 0% WGDC means the ECU is not bleeding off any boost and will thus run mechanical boost (upto ~10 PSI or whatever it is) assuming of course there is sufficient exhaust flow to spin the turbine fast enough to make 12 PSI of boost. Any WGDC above 0% means the ECU is bleeding off boost in attempt to make more boost than is currently being produced.
So, from that, the ECU cannot control boost via the wastegate solenoid if the desired boost were below the mechanical boost as dictated by the WGA spring. Thus, as already mentioned, the ECU does not target specific boost levels (when in Open Loop WOT) but instead targets load. The most direct way the ECU can control the load is via the throttle.
To answer someone's question... yes the AP should be able to remove this limitation as you can change the tables for load targets for each gear. Of course, you have to remember to turn off the DSC system -- as once it detects wheel slippage it will close the throttle to cut back power.
Someone else mentioned the 'wheel' being brought into the equation. If, by wheel, they meant steering wheel, that refers to the limitation of boost (though again, it probably limits load and not directly boost and I think any gear) when the steering wheel is turned. Not sure of the details -- in that I don't know if the limitation is adjusted based on steering wheel angle or if it's more of an on/off type thing. This, I don't think, can be adjusted by the AP (I could be wrong) because I believe it is done by the ECU logic and not the tables. It can be defeated I believe by disconnecting the steering wheel angle sensor.
snip
Very nice, thanks. I'll have to study your response more for understanding.
Jdizzle659
Member
- :
- Mazdaspeed 3
the way i figured it was that the electronic switches in the gear selection was limiting the boost (the ECU knows when the shift knob is physically in 1st and 2nd gear), and that all other inputs were for the TCS and DSC (like throttle input, steering angle, accellerometer, etc)
wonder if full boost can be achieved in reverse
I've hit about 12psi in reverse. Pulls harder than first gear plus it make your car RWD!
Stock, can't you turn off the DSC?
I believe if you hold the button and then turn the car on on, continuing to hold the button for a couple of seconds, not only will the tach read "DSC OFF", but you'll also see the picture that indicates a loss of traction (car sliding around). Both lights will be permanently on until you either turn the car off or re-engage DSC. That's what I read somewhere once, at least.
I believe if you hold the button and then turn the car on on, continuing to hold the button for a couple of seconds, not only will the tach read "DSC OFF", but you'll also see the picture that indicates a loss of traction (car sliding around). Both lights will be permanently on until you either turn the car off or re-engage DSC. That's what I read somewhere once, at least.
I believe 1st is limited to 9psi and 2nd 12. I don't see full boost till 3rd
Thats about right.
Nliiitend1
Member
Stock, can't you turn off the DSC?
I believe if you hold the button and then turn the car on on, continuing to hold the button for a couple of seconds, not only will the tach read "DSC OFF", but you'll also see the picture that indicates a loss of traction (car sliding around). Both lights will be permanently on until you either turn the car off or re-engage DSC. That's what I read somewhere once, at least.
The DSC is switched off even if you DON'T follow the instructions regarding "holding down the button while starting."
All you have to do is press the button.
...this has been discussed ad nauseum.
Similar threads
- Replies
- 1
- Views
- 2K
