Turbo FA in the new JDM Legacy, next WRX

[arghx7]

Originally Posted by OrbitalEllipses

A while ago, it was theorized on NASIOC that DI could be done without port injectors while still preventing carbon buildup on the valves through the use of a properly designed air/oil separator and valve timing. Voila, a Subaru patent for what sounds like an air/oil separator!

People assume that just because VW and some other early adopters of mass production DI had valve deposit problems, they all must have valve deposit problems. There are a lot of different air/oil separator designs that have been introduced for use with direct injection over the past few years. Jaguar for example has a more sophisticated system to limit the amount of gas flow and oil sent back to the intake side under different conditions. Heated and cyclone-type crankcase ventilation systems also mitigate the problem. All these solutions cost money though--development hours and higher part costs.

Originally Posted by serialk11r

I have a very hard time trying to figure out why in the world they want to make 300hp by using so much boost + a low rpm

The chart below is from a Delphi study on downsizing + downspeeding:



Here are the basic trends and relationships to understand.

1. Brake specific fuel consumption decreases at higher load and lower speed according to a basically logarithmic-looking curve.

2. Engine output is a function of displacement, brake mean effective pressure (load), and engine speed.

Therefore...

3. If we keep the engine speed the same but decrease the displacement, we must increase the brake mean effective pressure (load) to maintain engine output. Lower displacement means higher brake mean effective pressure to achieve a given output, which means lower fuel consumption.

4. If we reduce the engine speed, we must raise the brake mean effective pressure (load) again to maintain a given engine output. Raising brake mean effective pressure due to downspeeding reduces specific fuel consumption again.

The boosting system does present its own set of issues but downsizing means reduced pumping loss and reduced cooling loss relative to larger engines with more cylinders.

Certain tricks with cam phasing can also reduce pumping loss (late intake valve closing). The use of high levels of cooled external EGR (not sure if this engine uses it) essentially works as knock suppresant.

[Bristecom]

This engine impresses me! If the new WRX and STI have a version of this engine with that rumored electric turbo technology, it could be amazing!

But putting something like this in a light rear wheel drive car like the BRZ probably wouldn't go too well. Too much horsepower for the weight distribution would easily take this car from fun to scary. With all wheel drive on the other hand, it would be excellent. Too bad the chassis they put it in are always big and heavy 4 door sedans/wagons.

[old greg]

Originally Posted by serialk11r

I have a very hard time trying to figure out why in the world they want to make 300hp by using so much boost + a low rpm.

Because turbochargers can only be efficient over a certain RPM range. They wanted to have lots of torque at very low rpm which means having a small turbocharger. The downside to that is that the torque is going to fall off at high rpm, and that can clearly be seen in the provided torque curve. So the desire for low rpm torque indirectly means that engine will be unable to make torque at high rpm. So in order to achieve their power goals at a necessarily lower rpm they needed to run more of boost.

[SkullWorks]

Originally Posted by Dimman

Re-read his post. No D4-S. Single injector between the intake valves. Not up the intake tract. He is talking about conventional DI rather than the port/direct hybrid.

It appears you are correct, The language didn't specify Direct Injection, But I see linked documents (and now quoted) do specify that it will be Direct injection.

[STJ]

Originally Posted by old greg

Because turbochargers can only be efficient over a certain RPM range. They wanted to have lots of torque at very low rpm which means having a small turbocharger. The downside to that is that the torque is going to fall off at high rpm, and that can clearly be seen in the provided torque curve. So the desire for low rpm torque indirectly means that engine will be unable to make torque at high rpm. So in order to achieve their power goals at a necessarily lower rpm they needed to run more of boost.

Your right thats why they should add sequential twin turbo's like the old legacy had. Imagine that, twin scroll twin turbo with DIT!

[Spaceywilly]

Originally Posted by STJ

twin scroll twin turbo with DIT!

This is a twin scroll turbo with DIT, I think you mean twin turbo with DIT

By employing the newly developed twin scroll type turbo charger

[STJ]

Originally Posted by Spaceywilly

This is a twin scroll turbo with DIT, I think you mean twin turbo with DIT

Yes but i meant two turbo's both twin scroll, sadly subaru stopped using twins before they started using the twin scroll tech.

[old greg]

Originally Posted by STJ

Yes but i meant two turbo's both twin scroll, sadly subaru stopped using twins before they started using the twin scroll tech.

They only used twin turbos once iirc.

[Dimman]

Originally Posted by old greg

They only used twin turbos once iirc.

The infamous 'valley of death' motor. Apparently terrible transition from single to twin.

[serialk11r]

I was more wondering what the point of this very early peak torque was, because it looks like they're using the wastegate like crazy above 2000rpm.

I question the philosophy behind these very high boost at low rpm motors because it seems to me that they are very low speed optimized which is good for FE test cycles which are mostly looking at low acceleration rates and cruising (low load). I feel like the real world results (where people driving fast cars are more likely to actually use a bit more power rather than try to accelerate at the same rate as everyone else) would not see as much of an improvement. I guess for the OEM, all that matters is the window sticker and compliance with regulation.

[Dimman]

Originally Posted by serialk11r

I was more wondering what the point of this very early peak torque was, because it looks like they're using the wastegate like crazy above 2000rpm.

I question the philosophy behind these very high boost at low rpm motors because it seems to me that they are very low speed optimized which is good for FE test cycles which are mostly looking at low acceleration rates and cruising (low load). I feel like the real world results (where people driving fast cars are more likely to actually use a bit more power rather than try to accelerate at the same rate as everyone else) would not see as much of an improvement. I guess for the OEM, all that matters is the window sticker and compliance with regulation.

What about with the CVT, though?

[blu_]

Its just there for ease of daily driving. Most new engines make peak torque very early and sustain it for most of rev range. They are trying to create an engine that mimics a large displacement sedan/wagon's driving experience but with better fuel economy. I would also assume it helps with highway gearing on most cars. CVT's are a trainwreck to drive imo though, so I dont even want to think about how that would be affected on this car.

Remember its a Legacy, not a sports car.

[OrbitalEllipses]

Originally Posted by Dimman

The infamous 'valley of death' motor. Apparently terrible transition from single to twin.

Not a very well liked engine in Subaru circles for sure.

Originally Posted by blu_

Remember its a Legacy, not a sports car.

This engine reeks of H6 replacement, IMO.

[serialk11r]

Originally Posted by Dimman

What about with the CVT, though?

I haven't ever seen a CVT on a car at work, so I have no idea how quickly the gear ratios change, but if CVTs are very slow to shift then trying to get more low end torque would be better for response probably.