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Borg Warner R2S regulated 2 stage turbo in an NB Miata
This will be challenging.
I have been a SC person up until a couple weeks ago and had stayed away from turbos and all things turbo.. Black magic to me.
As soon as I decided to go turbo, I was handed a 2 stage setup by Mercedes Benz to install in the Miata, which pretty much ensures I will be asking a million questions.
This is not a request to spoon feed the Turk. I will research and throw things out there for everyone to chime in.
It will be an interesting exercise into uncharted waters. That should provide some entertainment for all of us.
Just the facts, ma'm:
Built engine with 9.0:1 JE pistons, M-Tuned rods, ACL bearings, all ARP studs, massively ported head, +1 mm Supertech valves (inconel on the exhaust side), Supertech double springs, Miataroadster guides, ported and polished intake manifold, Skunk2 TB, TDR intercooler, port water injection, oil squirter delete, coolant reroute, double core radiator with double fans, progressive port water injection, COP ignition, MS2e by Reverant, dual maps with "safe" settings in case of WI failure, DIY aluminum 3 piece undertray, electric Power Steering, big brakes, active, programmable suspension, delrin bushings, new paint job, and then some.
Here is are the turbo(s)...
And, one for size reference:
I have room in the engine bay, fitment is not a problem.
There is a local fabricator who happens to be a genius CFD savant, and he happens to be a friend of mine. He builds ultra high end manifold and exhaust systems and is well respected both here and abroad.
So far, everything seems very smooth...
Last edited by Godless Commie; 01-08-2018 at 11:46 AM.
I am, however, facing some interesting challenges:
This turbo setup features three separate controls. And get this: they are all VACUUM operated. Including the wastegate.
I mean, this setup is used in a diesel engine. Diesels have vacuum pumps, and the vacuum level never changes with RPM and such. So, a controller sends signals to some vacuum solenoids to activate the said controls...
The trick is figuring out the reasoning/triggers behind these individual commands.
Here is a short video of how the system operates, and you'll understand what I mean:
Small turbo is called High Pressure Compressor (HP), large one if Low Pressure (LP).
In the very beginning, HP spins and starts spinning the LP.
After that, LP starts blowing into HP.
Then, HP and LP blow together for a BRIEF period.
Following that, LP takes over, its bypass valve opens and LP continues to provide boost till either wastegate opens, or I lift my right foot.
The largest actuator operates a valve or gate between the two turbos.
This is an important step, because when and how it opens determines the boost ramp and how much the HP has to work:
Too little, and boost transition will be laggy and there will be a noticeable dip in the boost graph.
Too much, and EGT will rise due to restricted exhaust flow and there will be IAT issues, as well.
It is entirely possible to run this thing solely on the HP. This would just ruin the unused LP.
Next, there is the opening of the bypass valve (after the LP). That valve ensures the LP is no longer blowing through the HP and just providing boost in the traditional sense.
Apparently, there is a HUGE advantage to have the LP feed into the HP for a while to ensure maximum efficiency and cooler temps.
I am ultimately planning on maybe 14-16 psi boost pressure with this system.
I will run it in stages after the install.
First stage will be at the absolute minimum boost pressure that will ensure a "handshake" between HP and LP turbos.
That way, I can learn the intricacies of the system.
Also, I am planning on using a pressure driven (normal)wastegate actuator and linear motion DC motors for the remaining two.
I can drive those using my MS.
Question:
Can I find a pressure driven WG actuator that PULLS instead of pushing?
That would make my life much easier.
Question:
Can I find a pressure driven WG actuator that PULLS instead of pushing?
That would make my life much easier.
Maybe you could use a dual port actuator, and just hook the boost signal up to the port closest to the arm. However, I don't know how much travel a dual port would have in the wrong direction. When I get the chance I could mess around with mine, for science.
The owner of the company who gave me this gracious gift also told me he will rebuild the turbos in whatever form or spec my application requires in the case I run into efficiency/compatibility problems.
I will also be getting several spares of whatever I will be using.
That gives me some piece of mind.
Question on fuel and ignition mapping:
I am guessing I will not be using traditional turbo maps for this thing, because of its low (yet adjustable) spool characteristics.
How difficult (or stupid) would it be to cross the 100 kpa mark at cruise AFR (like, 14.5) and incorporate a very aggressive accel enrichment?
I am asking this stupid question, because this thing is capable of full boost at ungodly low RPMs.
Freeway cruising would yield zero vacuum (or thereabouts) and fuel economy would be horrendous.
Please tell me if this is a stupid argument.
I do not have much (if any) seat time with a ridiculously low spooling turbo, so go easy on me.
Well if any of us know anything, we know that it's common practice and highly advisable to build a turbo setup around some weird completely unsupported turbo(s).
Wait.....
But on a serious note: this is actually kinda cool, since you should definitely have enough talent to make it work.
PS: did you call me that one day? I was in a meeting and wanted to return the call but number was blocked.
I think the throttle is going to complicate things even more. One more HUGE variable that a diesel does not have. Crossover timing will change with both TP and RPM.
I think AFR / VE should still be based on MAP and RPM. Let's see, though. VE rows can be based on other "load" than MAP, so I wonder if some equation can be used to generate that "load"?
If you get it working, patsmx5 will likely take (2), please.
Me, I'm still at the, "would rather drive it than work on it" stage. Then again, I'm not well versed in Get it all done in 24 hours reality show type work.
Maybe you could use a dual port actuator, and just hook the boost signal up to the port closest to the arm. However, I don't know how much travel a dual port would have in the wrong direction. When I get the chance I could mess around with mine, for science.
Thank you, that would be awesome..
Originally Posted by 18psi
Well if any of us know anything, we know that it's common practice and highly advisable to build a turbo setup around some weird completely unsupported turbo(s).
Wait.....
But on a serious note: this is actually kinda cool, since you should definitely have enough talent to make it work.
PS: did you call me that one day? I was in a meeting and wanted to return the call but number was blocked.
This will definitely be a first if I can pull it off.
SClike response with all the niceties of a turbo.
And yes, it was me. I called over Skype, so I'm sure you saw a weird number.
I think the throttle is going to complicate things even more. One more HUGE variable that a diesel does not have. Crossover timing will change with both TP and RPM.
I think AFR / VE should still be based on MAP and RPM. Let's see, though. VE rows can be based on other "load" than MAP, so I wonder if some equation can be used to generate that "load"?
If you get it working, patsmx5 will likely take (2), please.
Me, I'm still at the, "would rather drive it than work on it" stage. Then again, I'm not well versed in Get it all done in 24 hours reality show type work.
I spend a lot of time in boost. (My WI tanks hold 16 liters of water, I run out in 2 days)
Therefore, I might leave the WG open in cruise conditions, or vent boost into atmosphere for fuel economy. That way, the WG will see a lot of action and will not get a chance to soot over and lock in place.
I'm pretty sure I can manage all that with the MS.
This whole gift thing was an unexpected benefit of the TV show.
(And, there's a whole another one coming up pretty soon on top of this one)
I read a lot of material where people just talk about RPM points for the above mentioned switchover controls.
That does not make sense without present load, "load request", selected gear, current pressures and temps and whatnot.
Me, I just want to boil everything down to primarily manifold pressure with a side serving of RPM, Coolant temp, IAT, EGT and knock.
Here, I found a couple of graphs for these controls:
I will try and translate all this into a usable signal for my car...
I also sent a pretty detailed email to Borg Warner.
Awaiting response.
Lots of info to digest here. I took a quick look at them. The first things I noted:
- If this system is for a diesel, will it be happy with the high EGTs of a boosted miata motor? (upwards of 900°C) Diesels have much lower EGTs.
- The plots in your post #15 show BMEP (roughly proportional to MAP and thus torque for a given displacement; approx 10 bar BMEP is equivalent to 100 kPa of MAP).
- A couple of number are needed will be needed to figure out if your system is a good match for a miata 1.8L motor - max gasoline engine HP at say 2 bar of MAP, at a reasonable efficiency, and minimum HP that will develop 1.5, and 2 bar of MAP (to give an idea of spoolup) without choking.
- it's tedious to figure it out from the photos... is your system equivalent to that on slide 6,7, or 8 of the above PDF?
- Controlling the 2 or 3 actuators to produce results superior to say an EFR6258 or a GT2554 or 2560 will require a separate DIY boost controller with custom code and possibly multiple pressure sensors. Be prepared for a bunch of engineering. (I built an analog controller to create a partial-custom boost controller, but that's another story). I don't know how easily such experimental code can be added to an MS3. Yes, standard (1-port) actuators *push* when they are fed certain pressures above ambient.
Lots of info to digest here. I took a quick look at them. The first things I noted:
- If this system is for a diesel, will it be happy with the high EGTs of a boosted miata motor? (upwards of 900°C) Diesels have much lower EGTs.
Not a problem. I have access to literally thousands of impellers - they can put together whatever is necessary, at no cost.
- The plots in your post #15 show BMEP (roughly proportional to MAP and thus torque for a given displacement; approx 10 bar BMEP is equivalent to 100 kPa of MAP).
I figured as much. They are running about 22 - 25 psi boost. I am targeting 14 -16 psi.
- A couple of number are needed will be needed to figure out if your system is a good match for a miata 1.8L motor - max gasoline engine HP at say 2 bar of MAP, at a reasonable efficiency, and minimum HP that will develop 1.5, and 2 bar of MAP (to give an idea of spoolup) without choking.
This, I will need your help with. Sorry.
- it's tedious to figure it out from the photos... is your system equivalent to that on slide 6,7, or 8 of the above PDF?
Mine is the one on Slide 8.
It is also explained (silently) in that YouTube video in one of the above posts..
- Controlling the 2 or 3 actuators to produce results superior to say an EFR6258 or a GT2554 or 2560 will require a separate DIY boost controller with custom code and possibly multiple pressure sensors. Be prepared for a bunch of engineering. (I built an analog controller to create a partial-custom boost controller, but that's another story). I don't know how easily such experimental code can be added to an MS3.
Why can't I just use different pressure levels produced by a single pressure sensor instead of multiple sensors? And, that sensor would be the MAP within the MS. Mechanical design of this system is nothing short of genius. I just need to figure out how to time the actuators, and maybe throw RPM, TPS or maybe accel in the form of delta MAP or delta TPS in there as a condition, right?
Yes, standard (1-port) actuators *push* when they are fed certain pressures above ambient.
Well, it can push.. All I need to do is figure the crank arm geometry for a pushrod then.
01-08-2018, 11:18 AM
Borg Warner R2S regulated 2 stage turbo in an NB Miata
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