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Supercharger bypass valve tuning strategies

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I wanted to open a discussion around how to approach the topic of setting up the tune for bypass valves that release the boost pressure back into the inlet manifold on supercharged applications.

I am running a Mercedes M113k on a MAXXECU Race which has support for the bypass butterfly valve but I am unsure of what the best strategy is for when to open and close.

You guys that have similar setups on this and other supercharged engines, do you close based on MAP, TPS, RPM? Do you go from 0% straight to 100% closed or ramping it? Or maybe you are doing something completely different and how is it working out?

I am grateful for any input on the topic.

I would also be interested in this

Original or Aftermarket (Kleemann etc) just curious because.... did the M113 really come with an OEM Kompressor in some models? I thought, no.

When I worked as an MB Systems-Technician, we were told, that the flap is opened (partly??) during light cruise in order to minimize pumping losses when no boost is required. Sorry, I do not have more precise details.

Hi Dom,

This is the M113K so the OEM Kompressor version fitted to the CLK DTM as well as the SL55, S55, CL55 and other later 55's. Power output ranged from 469bhp-574bhp depending on platform.

It had a system with double E-throttles where one butterfly valve is fitted between the intercooler and the inlet manifold to release boost pressure at certain points. I was hoping to get a discussion started regarding when the optimal time would be to open/close and what parameter to base the control off of.

I know that there are other engines/platforms running similar systems such as the Mini Cooper and Ford Lightning I believe (?) so hopefully this could help out more people.

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Hi Jon

now that you mentioned it, yes, the 113K of course. It was later superseded by the M157 4valve Motor. M113 had 3.

Nice photo btw.

Ah, I was thinking of it being used as the bypass valve to reduce pumping losses through the supercharger under light load/higher manifold/plenum depression. For that I would expect the closing point to be when the plenum depression approaches atmospheric.

In this instance, with it opening to limit boost by recirculating it, I would expect it to be operated to keep the torque output of the engine within the nominal limits of the transmission - note, that's based on references to them being "torque limited to protect the gearbox", and I may be incorrect. Depending on the AMG/Mercedes thinking, it may also be tied in to the traction control as a more elegant solution than cutting cylinders?

I have heard different theories but the most common ones is that the purpose is both connected to ESP as well as for aiding with heat soak and fuel consumption during idle and light cruise. The M113k supercharger also has a clutch for disconnecting the drive belt incase of high IAT etc.

Worth noting is that not all M113K came with a valve but some (the CLK DTM for instance) only had the clutch for limiting boost.

Some people running stand alones seem to only open the valve at 0%TPS but I am not sure how this would affect the longevity of the valve motor.

Opening at only MAP below atmosphere would kinda be the same but another way of doing it.

My goal is to have as fast of a response as possible but try to limit the risk of burning the valve motor from having it engaged constantly.

The fact that not all of the M113K had a bleed valve is, my assumption, emission related.

No need to overthink this topic IMO.

..also here, not to worry, the valve actuator is built to last and operate reliably for millions of cycles.

If your aim really is to minimize pumping losses, do it on a dynamometer observing torque output whilst changing flap positions during steady state running.

I will hopefully dyno the car in the coming months. My hope was to have the bpv at least somewhat functioning as intended before then to use the time in the dyno efficiently.

I was reading up on what whipple does with their bpv and that one seems to be vacuum actuated and used mainly to not have excessive pressures on the supercharger when the throttle closes and also to aid the supercharger at low rpm, minimizing parasitic losses.

If one were to go for something similar, would the best course of action be to let the valve open at less then atmospheric MAP only and not bother with other inputs such as TPS?

I have seen others with electronic bpv's ramping the closing over a set TPS value like starting to close for instance at 25% TPS and have it complete closed at 75% TPS. These numbers are of course only examples but does this look like a reasonable path to take and just fine tune the values after how the engine behaves?

I would say you would implement one of the strategies you outline above, and tune for those conditions. Then test the driveabliity. If you're not happy -- implement a different strategy, tune for that and test it's driveability.

I'm sure you will learn a great deal as you dive into this. I don't think there is a short cut -- do the work, find out what works. Good Luck!

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