VGT turbo VE compensation discussion?

[Aero]

I'm not sure where this belongs, wanting to get some thoughts on this.

I have this project going on running on MS2E using a Holset VGT turbo. I am using a wastegate actuator for the VGT actuation, and an external wastegate for keeping boost down after VGT is fully open.

Now I know that using SD computers anyone swapping turbos, or turbine housings will have to retune to match since it can greatly affect VE of the engine.

My problem comes from having a hotside on the turbo that can vary from a VERY small A/R, to a very large one, and anywhere in between. In Holset's measurements it varys between 3-4cm^2 all the way to 25cm^2.

Currently to avoid tuning complications at WOT and higher boost, I have the VGT opening fully before I would like to, so that at high engine load I have basically a fixed size turbine housing. Greatly simplifying tuning in that portion of the map. This slows my spool down somewhat from where it could be if ideal. It spools VERY quickly to 9-10 psi, then slows down because that is where the VGT is fully open.



My question is:
Is there any way the baro compensation, or something similar could be modified to allow a pressure sensor, a high pressure MAP, etc to measure exhaust manifold pressure and at least somewhat compensate for the resulting variation in VE?

I have another guy who is looking at using a Garrett VNT and MS2 also. I know something could greatly benefit him also.

I have some pictures and information about the turbo here.
http://www.turbotalk.org/bb/viewtopic.php?f=25&t=174

http://www.theturboforums.com/smf/index ... c=120273.0


Here is a MSLV log of the transient response of the turbo with the VGT opening faster than I would like. From 3000 RPM cruise at 70kpa to 9 psi in .9 second, then much slower after that. This response is in a turbo with a GT35R sized compressor on a 2.4l btw.


I would appreciate any feedback on possible solutions to the tuning complication.


*edited for links

[Fred]

No time right now to read through, but you copy pasted your post from another forum and the links are broken :-) Will read later or tomorrow.

[Aero]

Woops. Yeah I posted most of that on Msextra but nothing happened. haha

I think the links are fixed.

[jharvey]

My question is:
Is there any way the baro compensation, or something similar could be modified to allow a pressure sensor, a high pressure MAP, etc to measure exhaust manifold pressure and at least somewhat compensate for the resulting variation in VE?

I'd say there is definately a way, however I suspect your not looking to write your own custom code.

I'm not much of a MS guy, so I'm not all that familar with the gui, or how to make it do things. I'd say Fred is a good resource for that kind of question. I'd also say it's physically possible, but I would think you want to keep the baro compensation if you can, so perhaps you would want to get a signal in to the MS unit via alternative path. Do you have an unused analog path? I forget how many AN inputs the MS units have, but if you have an available input, you could make a side circuit, add a bit of code, and make it go.

[Fred]

Yeah, if you measure back pressure you *may* be able to figure out some function to compensate. The trouble is though, to get a good accurate representation you actually need a 3d grid not a contour and correction. MS baro is pretty average as is, but I'm sure you could make it work for you one way or another with an ex sensor. It can probably be approximated pretty well with some function.

(Still haven't had a good read/look yet)

Fred.

[Aero]

My question is:
Is there any way the baro compensation, or something similar could be modified to allow a pressure sensor, a high pressure MAP, etc to measure exhaust manifold pressure and at least somewhat compensate for the resulting variation in VE?

I'd say there is definately a way, however I suspect your not looking to write your own custom code.

I'm not much of a MS guy, so I'm not all that familar with the gui, or how to make it do things. I'd say Fred is a good resource for that kind of question. I'd also say it's physically possible, but I would think you want to keep the baro compensation if you can, so perhaps you would want to get a signal in to the MS unit via alternative path. Do you have an unused analog path? I forget how many AN inputs the MS units have, but if you have an available input, you could make a side circuit, add a bit of code, and make it go.

I would love to write custom code but unfortunately I definitely don't have the skills required for that. I suspect it will have to be new code too. I would definitely be happy to answer any questions I can, provide testing for any mods, logs etc although it will have to wait a little while till I get the car running again. I just don't have the skill to write the code or figure out the function etc.

If the backpressure is actually measured I think the baro compensation would be moot because that is basically what you are doing. Since baro correction is just compensating for exhaust backpressure variations due to atmospheric pressure variances(as i understand it anyway) So IMO replacing the second MAP sensor with something that would be compatible with the pressures involved would be okay. With suitable damping to prevent individual exhaust pressure pulses from causing issues (ie vacuum canister or orifice to slow it down for a mechanical solution) Using the second MAP input would remove the requirement.

It seems like a modification to the baro correction could at least provide some form of compensation, but obviously I'm not an expert in the inner workings of MS or any other EMS.

There is another gentleman on my forum who is testing a Garrett VNT from a powerstroke who is pretty interested in it too.

[Fred]

You are right, that is precisely what baro is for. You are compensating for changing VE due to back pressure with a guess based on atmospheric pressure. I've seen the effect of this during spool as the gate opens on my he351cw too. If we got something nice working I'd be interested in using it myself.

What I'm NOT interested in doing is working on MS2 code at all. There are a lot of reasons for that from my point of view. Perhaps start a thread in firmware on algorithms for back pressure based compensation and see who says what :-)

Fred.

[Aero]

You are right, that is precisely what baro is for. You are compensating for changing VE due to back pressure with a guess based on atmospheric pressure. I've seen the effect of this during spool as the gate opens on my he351cw too. If we got something nice working I'd be interested in using it myself.

What I'm NOT interested in doing is working on MS2 code at all. There are a lot of reasons for that from my point of view. Perhaps start a thread in firmware on algorithms for back pressure based compensation and see who says what

Fred.

I can understand that, especially since you are working on your own ECM. I'm sure if we can figure out the algo that I could get someone else to code it for MS2, and it would probably be adaptible to any of the other options too. I think it would be nice for anyone who may swap turbine housings helping prevent needing a complete retune.

As for your HE351CW comment.
Something I have really noticed with my setup. The VGT is fully open by 9-11 psi which happens fairly early in the RPM band. Right about where the external gate opens up(1bar spring), immediately after the gate opens I have to pull out a LOT of fuel as compared to before to keep the AFRs in the same range. I kind of wonder if dumping the exhaust instead of utilizing all of it is reducing the overall efficiency of the turbo system and reducing VE significantly. My first thought was sucking some exhaust from the dump back into the engine but that is not possible with my intake setup.

[Fred]

I had the opposite! With the exact same boost and a bunch less ex back pressure I had it go more lean, not more rich.

I suspect a change in housing might make you need a retune anyway if you weren't already adjusted for it. When you tune yours you will be aiming to have the same effective housing size at any given point in the map over time. It just won't be the same housing size between X RPM and Y RPM etc.

Fred.

[Aero]

I had the opposite! With the exact same boost and a bunch less ex back pressure I had it go more lean, not more rich.

I suspect a change in housing might make you need a retune anyway if you weren't already adjusted for it. When you tune yours you will be aiming to have the same effective housing size at any given point in the map over time. It just won't be the same housing size between X RPM and Y RPM etc.

Fred.

The way it works now its the same size housing at a given boost level. That is if you take out of it the effect of exhaust pressure trying to force the VGT open, and I'm not sure how much that changes it.

I'm not sure what was causing me to have to lean it out so much, that was just speculation on my part. I'm not sure if there is anything else in my setup that could cause it that I haven't thought of yet.