Sequential Turbo Sizing - CJAA Engine

[nate0031]

I have a CJAA that I swapped into my C5 A6 Quattro. It's been a great running engine so far, still with the stock BV43 turbo. Eventually, I would like to upgrade the stock turbo so I can get much more power from the motor, but being that it's moving a larger car, and that I tow with it, I am reluctant to lose the low-end torque/quick spool. As such, I'd like to build a sequential setup, similar to what the Bi-Turbo Amarok uses.

I played around with the idea of using the Amarok piece, but they all appear to be of the oval port design. From what I read, retrofit is too difficult to be practical, and I'm a bit reluctant to spend the money and find out for myself. Also, the big turbo only seems to be about a K04 in size, it still wouldn't maximize what the rest of the motor is capable of.

I recall mentioning this to someone, and it was suggested rolling my own may be the best option. That it might be done for a decent price as well if I can do the fab work. This sounds right up my alley, but that means I need to pick the best turbos for my application, and I know fairly little when it comes to sizing turbos.

Hence my post! My main questions would be:

Since I wish to do a sequential setup, is turbo size of the same importance as with a compounding setup? Being that the end goal is for the large to essentially bypass the small?

Are there any particularly good reads on how to read turbo maps? And how to select two to work together?

Based on what others have done (albeit compounding), It looks like it's easiest to stick with wastegated units vs VNT. I already have a Teensy and Raspberry Pi in the car for other purposes (cruise, CAN interface, dash display), and would like to use the Teensy to control the wastgate(s). Is it possible to use the ECU's N75 output as a boost request input to the Teensy, which then uses a PID controller or such to control the wastegate(s) and obtain the requested boost? I'm not sure how the ECU's logic works, and if it would actually allow the use of the N75 output as a simple boost request.

What I would love if it's possible, is to have the first turbo coming in strong by 1500 RPM's or earlier, while having a large enough turbo for it to not become anemic at ~4500 like the stock unit. I'd hope for the setup to be capable of 250-300HP, while still spooling fast and early. With my limited knowledge though, I don't know how practical and/or possible this is.

Thanks for any insight!

 

[GOFAST]

If its not gone be plug and play anyway.
Why not try a GTB2260VKLR ?

What you ask / want.......is the hard way.

 

[nate0031]

What you ask / want.......is the hard way.

Lol, no argument there. It may not be feasible or practical, but was an idea I wanted to at least try and chase down. One of my biggest questions at this point is, can the N75 output just be used as an input to another controller. I don't know how the ECU's logic works, but it'd be easy to have another controller read the N75 duty cycle and interpret it as requested boost. I imagine using another controller to run the multiple wastegates etc that may be required. Ergo, multiple devices could be controlled precisely to obtain requested boost based on the N75 duty cycle.

I've also been strongly considering a GTB2060/2260vk or vklr. I haven't ruled out those as options as they would land me in the power range I'd like. I just worry about response down low when towing. When getting a load going, I don't usually rev over 1,100-1,200 RPM so as to not stress the clutch. So if the turbo doesn't build boost well at low RPM's, it's going to be a bit of a pain every time I stop and start. For that reason, and looking at dyno charts from variants of the 2.0 CR like the Amarok BiTurbo, I'd love to achieve similar performance if it isn't too impractical.

I really need to read up on sizing turbos. I happen to have a K03 from a 1.8t laying around, but have no idea if that would have any place in such a setup.

 

[JFettig]

GT2860 or GT2871 right below the stock turbo would be a decent size for compounds but you'll need a bypass wastegate.

N75 is not a fixed output, its a fully closed loop system.

If you run dual wastegate turbos, they'll basically take care of themselves if they're sized correctly and set where they need to be set.

If you want to set up an Arduino setup, you'll need throttle input(easy), RPM, (easy) and 2 boost signals - also easy. It just needs to have maps calibrated properly. You won't get a load signal or boost request signal out of the ecu anywhere that you can use I'm afraid, unless you can somehow read measuring blocks over CAN and get the nm request as your input.

 

[KERMA]

the factory already figured it out for you. No need to reinvent the wheel.
git thee the CUAA turbos.
Since you are willing to fab and DIY.

Boom, done.

 

[Macradiators.com]

Agree with Kerma, get the CUA turbos and you are ok for 300hp with some modifying, porting etc.
I would choose the easy way, 2260VK or VKLR for faster spool.

 

[nate0031]

N75 is not a fixed output, its a fully closed loop system.

Thank you. Had a feeling getting some sort of control output wouldn't be so simple. With a GT2860 or GT2871 over the stock turbo, is tuning the VNT on the stock turbo tricky?

Thanks everyone. Can anyone comment on what's needed to adapt a square port manifold to a round port head? The bolt patterns look similar, but I could not find pictures good enough to really compare the two. Would love to see the gaskets laid together.

How early does a VKLR really start to spool?

 

[turbobrick240]

I think the 2260vklr starts spooling up around 1400 rpm on a 2L tdi.

 

[GOFAST]

https://youtu.be/k0NX4m1RD9s

 

[turbobrick240]

Based on the dyno charts I've seen, it looks like a journal bearing 2260vk begins to outperform(torque and power) a bone stock cr140 around 1900 rpm.

 

[Fix_Until_Broke]

I'm currently building something very similar although on my ALH so a few generations older. If you check out the most recent posts in my "Where to Stop" thread, you'll find some info. I don't have a lot of documentation on the turbo sizing in that thread, but have been through all the math to believe that I will be able to havea power band from ~1500 to ~4500 RPM in full compound without going to sequential.

I also have a PD engine with a GTB2260VKLR on it. While it is true that it will spool in the 1700-1800 RPM range, the transient response is a whole different ballgame. I wouldn't want to tow anything with it, especially if there are rolling hills. I've been running the GTC1444VZ as a single for a couple years now and it will also build 20 psi at 1700 rpm just like the 2260, however does so as you're pushing your foot down, but consequently is out of breath by 3500 RPM. The 2260 pulls hard all the way to 5000, but doesn't really get going until 2200 or so.

Given that you are running a CR engine you have many benefits that I don't such as really good fuel delivery and atomization at low rpm, 16 valve head, larger rod journals, etc that are all helpful for your goals. Due to this, you will likely see better performance at lower RPM than I do, but I can't predict how much. I did drive Jfettig's CR with a GTB2060 and it did strike a very good balance between transient response, low rpm drivability and high rpm power. He does have a lot of time in getting it dialed in.

I will say that if you can do it with a single turbo, that is by far the most practical solution. I've got 45-50 hours just in fabrication and still have another 20 left, and have at least as much time in the mathematical side and we have not even begun tuning it yet. I'm not trying to dissuade you, just informing. This isn't like the duramax, power stroke, cummins world where you can write a check, bolt on the parts that show up on your doorstep, update the tune and be done.

If you can find a 2260 on a CR that has been properly setup and tuned to take for a drive, that would be your best next step.

 

[JFettig]

Nate,

The bolt pattern for the rectangular port head is quite a bit different from the round port head. I think you'd have better luck swapping heads.

I do have manifolds that will fit GTBXXXXVK bottom mount on your head, just takes slight modification(minor). You might have to modify that motor mount for it to work - I can't say for sure until someone tries to mount it.

Matt - Mine is a GTB2056VK that you drove. That tune is close to the standard Stage 4 tune for that turbo, the main customization are on the top end(over 5200rpm). One of the big differences between our TT and my JSW is the injection system, possibly head flow. Its still going to be better than a 2260 regardless.