Turbo engines

[tt911er]

About from supercharger bypass.


"With the throttles placed after the positive displacement supercharger, the design of a very smooth progressive air bypass system becomes extremely important."

I,m unable to bypass the S/C to before primary intercoolers(coolers after turbo) because those are outside of the engine compartment. With individual throttles I have no choice but dump the bypass air to the atmos?
Even if I could bypass it before primary I/C that area is still "closed" pressurised area ( from pressure side of turbo to throttle plates) and pressure from turbo will hit against closed throttle plates? Or have I missed something. Probably;)
I have played idea of leaving Eatons own Flapper valve (that I can control via engine management box) for additional options but use the wastegate-bypass from plenums connection pipe for a main control. For a early phase that flapper valve should be just leave closed to minimize the variables.

I have difficulties to understand how I could bypass the air from S/C pressure side to "closed pressurised area" without boost spikes

Juhani

[Tony]

However you decide to do it, the pressure after the supercharger will need to be relieved when the throttles are either closed, or running only slightly open.

Just venting to atmosphere will certainly work, but the noise level coming from the supercharger rotors will be higher than you are probably expecting.
It will be a most annoying drone that rises and falls in volume with throttle opening. The less throttle, the louder it will be.
And its an unusual sound that readily attracts attention.

Circulating the air directly around the supercharger works too, but it has the disadvantage of heat buildup in the supercharger under light throttle running.
The same air goes repeatedly around through the supercharger picking up a bit of extra heat each pass.

There are quite a few possible solutions, it depends mostly on detailed layout and what you can do with what you have available to work with.
Its all a heat and noise problem at small throttle openings.
Flat out it's going to make a LOT of power, and the bypass will be totally closed.
How the bypass plumbing details finally end up is not really a performance or drivability issue, its more the annoyance factor of having something that could behave better than it does.

[brandoracing]

Good.
I want to return to the first talk ot Mr Vaught.
Why some turbocharger producer have flow map of his compressor in CFM?
I ever works with lbs\min but the IHI use a CFM in air scale.
this disorientate me.
What is the connection between CFM and LBS\Min?

[tt911er]

Good advise, I haven't thought about much the noise factor. Have you seen the Ron's "world fastest Lotus" in Youtube, it has pretty high noise when enginebraking. That might be the noise you talk about?
I could easily release the pressure from plenums to connection pipes after the turbo intercoolers, those will be located near by.
BUT that will release only "second" state pressure producer. How about the pressure between turbo and throttle plates? Does the area inside the piping give enough area for "turbo dump". Also is that larger circulation area around S/C enough to solve the heat issue? Dumping it just out of the pluming will totally solve the heat issue but gives the noise.
How fast the pressure will equalize inside induction system? I mean how much it has effect WHERE you do the bleed out? If there is noticeable or even some lag for pressure spread then it might have some benefit to do it close as possible from throttle plates?

About the turbos, biggest compressors from Garrett gt35 start to be "on the area". Holset hx40 looks even better. Outer dimensions of those will become an issue, that's for shure!

Juhani

[Tony]

There will not be much (if any) buildup in pressure from totally blocking turbo flow.
Turbo boost is pretty much a function of compressor tip speed.
Only reason to fit a blowoff valve to a turbo is to keep the compressor well away from the surge area.

A roots blower is a very different beast. Block the flow on the pressure side, and the pressure will rise until something breaks.
Usually either a hose blows off, the drive belt shreds or catches fire, or the intercooler explodes.

How fast the pressure will equalize inside induction system? I mean how much it has effect WHERE you do the bleed out?

The bypass placement will have zero effect on drivability.
How it opens and closes, at what throttle positions it opens and closes will be determined by the spring, (if you use a wastegate as a bypass). And that will influence the relationship between throttle position and available boost.
There does not seem to be a time factor involved, at least I have never noticed any delay.

Pipework volume is an interesting topic in itself.
With a turbo excessive pipe volume can certainly effect turbo response.
With a roots blower the effect is far less and is not really such a big factor.
Far more important is throttle placement, and the biggest effect is not during throttle opening, but throttle closing !

As you will be running a beautiful set of Porsche individual throttle bodies, pipe volumes up stream of those can be ignored.
You will discover twincharging has very fast throttle response, even with a plenum and single throttle.
The set up you have will be even better.
So don't worry about pipe volumes up stream of the throttles, it is a non issue with twincharging.

What is the connection between CFM and LBS\Min?

CFM x 0.0765 = Lbs/minute (at standard sea level pressure of 29.92 inches of mercury and 60 degrees Farenheit)

[Tom Vaught]

Still doing Boosting Work. This year is 38 Years at the game. ECOBOOST is going strong!

That being said, Have learned a lot about Flow Benches over the years and Boosting over the years.
Deal is they both are similar in that you really need to specify your goals and decide what you really need for your application.

I have friends with cheap $800 Borg Warner Diesel type turbos on street car engines that routinely can make 750 - 800 Hp
without breaking a sweat. Course the fab work to install the turbo and related parts took some thinking and effort. They are happy guys.

Same deal goes for building a flow bench for your application. Is it a "Research" deal, a 'Hobby" deal, a Racing deal to verify that what
you paid for was what you got at the end of the day, or a "Do It Yourself" Turbo engine and Hot Rod Flow Bench deal.

At the end of the day, did you learn anything, did you save money and still get what you wanted, did you achieve your goals for the project?

Tom Vaught Senior Engineer (ECOBOOST Programs)