Variable-geometry Turbo and Quick Spool Valve
 

Hi Guys,

Has anyone experimented with Variable-geometry Turbos and/or Quick Spool Valves on rotary engines? I was thinking if we were to use a variable-geometry turbo and or quick spool valves + twin scroll manifold we could possible get the low RPM response of a stock twin turbo system and the up top end power of a big single. In other words we could go big single and have the response and power of a stock twin turbo system at low RPM and still have the benefits of a big single.


Moe Greene

Yeah, at least one person has used the Holset VGT turbo (HE351VE) as it works by pulling the vanes into the cooled center section, so it is reliable on a rotary.

The response was great and it make boost with no load, but the spool (max boost available at set rpm) wasn't that spectacular because it was limited by the compressor surge line.

That is the problem with singles and even more so with parallel twins.

The sequential twins skirt this issue by using a smaller compressor at low flow levels for the good compressor surge line.

Another issue with VGT is the Volumetric Efficiency of the engine changes as the exhaust restriction changes. It would be best to pair it with a Mass Airflow Sensor as well as Manifold Absolute Pressure.

If you do an RPM stepped system like Mazda 1987-88 RX-7 turbo (quick spool valve) then you can just tune MAP as the VE will change at a set RPM.

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I think the best for spool would be a variable volume and variable AR system so that it keeps the exhaust velocity up in the low RPM.

My idea for my EFR 7670 was to use the stock 1993-2002 RX-7 sequential turbo manifold as the "quickspool valve".
At low rpm the exhaust would follow the route to the stock primary turbo in the manifold and then into the front runner of the single turbo manifold to the front turbo scroll. At a set RPM the turbo switching valve would open the flapper to allow exhaust into the rear single turbo manifold runner to the rear scroll as well.

You would have to run dual wastegates (internal or external) to make it work.

I guess the response wasn't that great either.

Here is the HX35 VGT. 4th gear pull from 3,200rpm.

Here is my EFR 7670 on HKS T04Z manifold for comparison. I do 5th pulls, 4th pulls and 3rd pulls. The 5th pulls from 3,200rpm slays the response of the VGT turbo pulling 3,200rpm in 4th. It spools literally twice as fast. If you aren't familiar with the Greddy boost gauge 0.5 is ~7.5psi, 1.0 is ~14psi, 1.5 is ~21psi and it was maxing 26psi. So about the same sweep as in the VGT turbo.

The EFR 7670 compressor flows a bit more I think than the HE351VE, but the flow potential of the opened up VGT exhaust housing on the HE351VE should boost the overall system VE.

Mazda used a quick spool valve from the factory for 87-88 model Turbo engines.

This is the type of turbo being used in the new Porsche turbo motors, correct?

So, what brand turbos are Porsche using and are turbos like that available to the aftermarket yet?

Porsche is using Variable Geometry Turbo, yes; but not the same design.

The Porsche uses Borg Warner VGT which uses variable pitch vanes moved by a swash plate like the Ford 6.0 VGT turbos (GT37VGT), it is too fragile for the rotary exhaust heat.

Yes, BW offers aftermarket VGT turbos, but

Variable turbine geometry (VTG) | BorgWarner Turbo Systems

Interesting, thanks.

BLUE TII, thanks for all the input. I've got an idea I want to bounce off of you. Busy with mid terms this week, as soon as they are done I'll give you the details.