I've been changing springs/pulling wastegate while I've been tuning, but then I realized that I had a spare N75 valve from an Audi. I'm thinking about installing a 3-4lb spring and letting the MS control boost.
If I configure generic port PT6-IAC1 for:
Variable: map > 130.0 Threshold, 8.0 Hysteresis
Power on Value = 0
Threshold Value = 1
This will switch +12V from IAC1 output when my MAP exceeds 130kpa, correct?
Also the N75 impedance is 30 ohms, so that should be .4A @ 12V. The IAC output driver should be able to handle this, correct?
For some reason I had it stuck in my head the MS2 didn't do boost control. However this seems like a decent solution.
Thanks,
Tom.
Driving other solenoids from IAC1 or 2.
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Read the manual to see if your question is answered there before posting. Many users will not reply if the answer is already available in the manual.
If your question is about troubleshooting, configuration, or tuning, you MUST include your processor type (MS-I or MS-II) and code version in your post. If your question is about PCB assembly or modifications, you must also include the main board version number (1.01, 2.2 or 3.0).
If you have questions about MS1/Extra or MS2/Extra code configuration or tuning, please post them at www.msextra.com Such questions posted here will be moved to: a temporary MSextra sub-forum, where they will be removed after 7 days
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rabiddeity
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It seems nobody has replied to this yet, so I'll chime in with what I've read.
I don't think this setup will work very well, but explaining why will take a bit of time. Bear with me.
First, why not use just a mechanical valve set to 14 psi or whatever boost you want to make? Well, mechanical valves aren't precise on/off devices. A valve like that would start to open around 11 or 12 psi and then be fully open by 14. So depending on how hard you're nailing the throttle you might see 11 psi or you might see 14 psi. Solenoids and electronic control allow us to be more precise, holding the wastegate closed fully until the absolute last moment.
In most cars there is a solenoid and an actual mechanical wastegate. The mechanical wastegate is activated when manifold pressure exceeds some low preset; usually it's around 7 psi but for low boost applications that number might be 3 or 4 psi. The solenoid sits between the manifold and the mechanical wastegate actuator. If you open up the wastegate solenoid completely, then the wastegate's actuator sees whatever the manifold pressure is. If the solenoid is held completely closed, the wastegate will never actuate (and your engine will destroy itself from overboost). So the solenoid is usually pulsed slowly (between 30 times a second and 60 times a second, depending on the valve). As it turns out, if we can control the duration of the pulses (called the "duty cycle"), we can set how much pressure that wastegate actuator sees, and thus control the wastegate quite effectively, assuming we've got enough manifold pressure to activate the thing. (This is why the wastegate actuator is set for a low psi rating and not your car's maximum boost.)
Most real boost controllers (both integrated and aftermarket) use some prediction in combination with the duty cycle to regulate the exhaust bypass. This prediction is important because in the real world the wastegate doesn't open instantly; it takes time for the solenoid to open, the pressurized air to hit the actuator, and the exhaust pressure behind the turbine to dissipate. This time isn't constant; it depends on the rate of increase of boost, so some rather complex calculus is used to predict when to start opening the wastegate. During this time, the turbo is still producing boost. If you've stabbed the throttle hard, the boost pressures are still increasing. If the boost control system doesn't anticipate properly, the system will overshoot the target. This usually isn't fatal, but it puts a lot of strain on your car so it's best avoided.
With the simple boost control you have outlined, your car will overboost well past 130kPa. MS-II will wait until the MAP hits 138kPa (130 plus 8 hysteresis), and THEN it will activate the solenoid. Boost will wildly overshoot, and the wastegate valve will open fully. Boost will drop far below 130kPa, and then the wastegate will close again (after MAP passes hysteresis). It will continue to oscillate like this for quite awhile. Setting hysteresis higher will only make the oscillations more wild. Setting it to 1 or 2 kPa will allow the oscillations to settle eventually, but you're still going to have massive overshoot, and it may even damage your solenoid if the pulses are too quick. (Ironically this can settle into a natural acceptable duty cycle if you can measure it, but there are better methods.)
In short, you need to be VERY careful when using a simple nonpredictive setup like yours. It will always overshoot, so you need to take that into account when telling it when you want the boost solenoid to activate. If you play it safe, boost will settle down to about 20 or 30kPa below your ideal max boost. It's not ideal, I know... for now you might want to just stick with the mechanical wastegate springs. Oh, and if you're designing the system from scratch, a reminder to make sure that when the solenoid is unpowered the wastegate actuator sees manifold pressure. You probably knew that already, but I figured it wouldn't hurt to mention it again.
This isn't really the place to discuss it, but the boost control for MS-II/Extra isn't even done yet, and I'm not even sure if the B&G code will have it for a long time, if ever. Trust me, I'm waiting on it too, while comparatively rare setups like nitrous control and water injection get written in... sigh. But that's a discussion for another forum.
I don't think this setup will work very well, but explaining why will take a bit of time. Bear with me.
First, why not use just a mechanical valve set to 14 psi or whatever boost you want to make? Well, mechanical valves aren't precise on/off devices. A valve like that would start to open around 11 or 12 psi and then be fully open by 14. So depending on how hard you're nailing the throttle you might see 11 psi or you might see 14 psi. Solenoids and electronic control allow us to be more precise, holding the wastegate closed fully until the absolute last moment.
In most cars there is a solenoid and an actual mechanical wastegate. The mechanical wastegate is activated when manifold pressure exceeds some low preset; usually it's around 7 psi but for low boost applications that number might be 3 or 4 psi. The solenoid sits between the manifold and the mechanical wastegate actuator. If you open up the wastegate solenoid completely, then the wastegate's actuator sees whatever the manifold pressure is. If the solenoid is held completely closed, the wastegate will never actuate (and your engine will destroy itself from overboost). So the solenoid is usually pulsed slowly (between 30 times a second and 60 times a second, depending on the valve). As it turns out, if we can control the duration of the pulses (called the "duty cycle"), we can set how much pressure that wastegate actuator sees, and thus control the wastegate quite effectively, assuming we've got enough manifold pressure to activate the thing. (This is why the wastegate actuator is set for a low psi rating and not your car's maximum boost.)
Most real boost controllers (both integrated and aftermarket) use some prediction in combination with the duty cycle to regulate the exhaust bypass. This prediction is important because in the real world the wastegate doesn't open instantly; it takes time for the solenoid to open, the pressurized air to hit the actuator, and the exhaust pressure behind the turbine to dissipate. This time isn't constant; it depends on the rate of increase of boost, so some rather complex calculus is used to predict when to start opening the wastegate. During this time, the turbo is still producing boost. If you've stabbed the throttle hard, the boost pressures are still increasing. If the boost control system doesn't anticipate properly, the system will overshoot the target. This usually isn't fatal, but it puts a lot of strain on your car so it's best avoided.
With the simple boost control you have outlined, your car will overboost well past 130kPa. MS-II will wait until the MAP hits 138kPa (130 plus 8 hysteresis), and THEN it will activate the solenoid. Boost will wildly overshoot, and the wastegate valve will open fully. Boost will drop far below 130kPa, and then the wastegate will close again (after MAP passes hysteresis). It will continue to oscillate like this for quite awhile. Setting hysteresis higher will only make the oscillations more wild. Setting it to 1 or 2 kPa will allow the oscillations to settle eventually, but you're still going to have massive overshoot, and it may even damage your solenoid if the pulses are too quick. (Ironically this can settle into a natural acceptable duty cycle if you can measure it, but there are better methods.)
In short, you need to be VERY careful when using a simple nonpredictive setup like yours. It will always overshoot, so you need to take that into account when telling it when you want the boost solenoid to activate. If you play it safe, boost will settle down to about 20 or 30kPa below your ideal max boost. It's not ideal, I know... for now you might want to just stick with the mechanical wastegate springs. Oh, and if you're designing the system from scratch, a reminder to make sure that when the solenoid is unpowered the wastegate actuator sees manifold pressure. You probably knew that already, but I figured it wouldn't hurt to mention it again.
This isn't really the place to discuss it, but the boost control for MS-II/Extra isn't even done yet, and I'm not even sure if the B&G code will have it for a long time, if ever. Trust me, I'm waiting on it too, while comparatively rare setups like nitrous control and water injection get written in... sigh. But that's a discussion for another forum.
I very appreciate your post. The more I thought about it, the more it seemed like I wouldn't get away from boost spikes or I would set myself up for the valve not opening and the turbo generating 30PSI....... That would be spectacular to watch, but I decided against it.
Your post just confirms it.
So, I have delta gate waste gate/6 lb spring/manual boost controller controlling manifold reference to the top of the wastegate, with the bottom directly connected to manifold [another issue, I need to find some vacuum line check valves..... ] It pops @ 10 PSI, it doesn't spike. Close enough for government work.....
In any case, appreciate your feedback and detailed explanation. I do plan on driving water injection with this as well, so hopefully that'll work out a bit better.
Your post just confirms it.
So, I have delta gate waste gate/6 lb spring/manual boost controller controlling manifold reference to the top of the wastegate, with the bottom directly connected to manifold [another issue, I need to find some vacuum line check valves..... ] It pops @ 10 PSI, it doesn't spike. Close enough for government work.....
In any case, appreciate your feedback and detailed explanation. I do plan on driving water injection with this as well, so hopefully that'll work out a bit better.