This looks like a promising way to get quicker spool using a large hotside while maintaining low emap up top. The size of the bypass port to the 2nd scroll may need optimizing, but the idea seems compelling. Wondering if anyone here has experience with something like this? It would really simplify header design... Just make a merge collector with a v-band. The Spool Valve holds all of the plumbing complexity, for wastegate, spool valve and turbo mounting. My main worry is about transition smoothness.
https://shop.elmerracing.com/billet-...t4twin-wg.html

 

Turblown was developing a really cool exhaust housing for the EFR line that incorporated a variable A/R scroll bypass.

Hasnt gotten anywhere in years and if I had to guess reasons why it would be-
1) there is no way to make sure your users set up rpm sensors and safeguards so you dont overspeed the compressor and especially more fragile EFR exhaust wheel.

2) the most popularsizes (EFR 8374/9180 and variants) already can spool to their surgeline on a 2 rotor without help and you have to ramp boost in to prevent catastrophic failure on many set-ups.

 

You really want to using an IMP:EMP based load model for that to work well and even then you will likely be skirting compressor surge, control strategy to avoid surge or midrange fall off probably needs a bit of control mapping around it, probably best with an intake side balancing/bleed off too. If you are going to run 2 wastegates you are almost certainly better off just having a fully divided manifold and turbine housing if it's a peripheral port 2 rotor. Probably more value on a renisis or 20b.

For all that effort to get a modest gain, I'd rather wrestle with packaging a low PR rise compound supercharger setup.

 

My idea for a variable volume (to increase low rpm exhaust velocity) and variable A/R turbo system is as follows.

Use stock FD sequential turbo manifold with divided runners off primary turbo and 2ndary turbo mounting flanges. Wastegate mounted off prespool runner or one on each runner.

At low rpm all exhaust flows through the front runner to the front scroll slot of the T4 divided turbo. At selected rpm the sequential flap opens and the rear runner and rear turbo scroll.

This keeps exhaust volume lower at low rpm so increasing exhaust velocity and spool.

One would use the 1.45A/R exhaust housing as resulting 0.7525 primary A/R is already small. Any smaller would choke most 2 rotor set-ups before 3,000rpm.

If it was chuffing through a 2" exhaust and a couple cats like stock, 1.05AR would be OK.

The S4 TII used a switching variable geometry exhaust housing and on any TII with exhaust mods the plain divided S5 TII turbo has more low end since the S4 primary AR is so small it chokes the flow early at over stock power levels.

 

Concern with overspeed is a very good point. Something like this probably makes the most sense for an RX8 or a 3 rotor that always run undivided manifolds or on a 13B J-bridge or Semi-P with a huge turbo like a GT42 or something, like Lag-atha here =>

 

Big turbo compressors will be less suited to quickspool valves than smaller compressors.

You can plot 13B on various compressor maps to see the max boost at various engine rpm relative to the compressor surgeline.

You can gain turbo response with a quickspool valve, but the surgeline will be a hard limit on how much boost (power) you can achieve at any rpm point.

You need to get into compounded compressor systems to overcome the surgelines. Garrett has a double compressor turbo for this and others use two turbos.

 

Been there and done that.
It made 0 difference.

We had more success with a throttle body on the compressor side to help the turbo past it's surge limits.

 

Very interesting. I had never hear of this, but looking into it found it being called a DVP in an old RX7club thread. https://www.rx7club.com/single-turbo...-turbo-617321/
1984 Patent: https://www.freepatentsonline.com/4471616.pdf
Simplified explanation of operation: https://cliosport.net/threads/anyone...riable.266246/
Photo of an old mechanical version: http://www.gurneyflap.com/Resources/2ndpart.jpg from BMW Turbo F1 Engine

 

https://www.rx7club.com/single-turbo...26%25-1062575/

 

Mazda had a "Quick Spool valve" from the factory from 1987-1988 on Turbo II's. They just called it a twin scroll actuator, but it had divided turbine housings with two different A/R, and the below actuator built into the manifold. They abandoned the design for a normal twin scroll in 1989, shown below with divided manifold (equal sized passages instead of small and large).




So it went:

12A turbo - standard open single volute single scroll
13B turbo 87-88 , variable A/R twin scroll with actuator as above
13B turbo 89-91, standard twin scroll with fully divided manifold and housing

then you had sequential systems with two different sized turbos (20B-REW) and two same sized turbos (13B-REW, with smaller turbos for the Cosmo compared to the Rx-7)