[Diy_efi] turbo "throttling"

[Gerard]

> The AR wouldn't change, I don't think, depending on the entry to the turbo.
> However this is based on my assumption that the housing is only divided at
> the entry port.  If the housing is divided throughout its entirety (like the
> whole 'conch' shell of the turbine housing has a division in it around the
> impeller) then, yeah, you kinda have two AR's, but I don't think that's how
> they work...?

I'm no turbo expert at all. I am dabbling in my first turbo project and
I am relying on loads of help from people who know more, but I do
understand a few basics.

Ever considered what would have to happen to the exhaust flow from
manifold to turbine house at the split? Say the exhaust gas comes down
the runners to a collector and then is normally "sliced" by the turbine
housing divider, now if you go and shut off one of those openings what
sort of flow would the gas have to take? Wouldn't it slam right into the
throttle you are thinking of?

Also, suppose the scroll is divided along its length. This would come to
2 tubes pumping gas onto a turbine at essentially 2 different points. If
you shut off one of them then what part of the turbine wheel will get a
larger dose of gas pressure? I am not sure on this as I don't know
divided turbine housings so can't say if they are split and eventually
become one before releasing gas onto the wheel.

I reckon if you're after controlling the A/R of the turbine housing then
why not look towards variable turbine vane technology. Some BMW
turbodiesel vehicles use these and Corky Bell seems to like the Aerodyne
items. Basically, vanes along the scroll of the turbine change the angle
of incidence at which the exhaust gases hit the turbine wheel. For low
rpm the vanes face the gas almost directly onto the wheel causing them
to spool everything up quicker. At high rpm and gas flow the vanes
direct gases more along the scroll allowing for greater torque applied
onto the turbine. You get the best of both worlds. An incredibly fast
spool up while using a large A/R turbine housing, and you still have a
large turbine to allow easier flow for high power output.

Pricing I hear is steep, but do some searching online for 'VATN turbo'
or something like that.

When I first read your post I thought you were thinking of taking
exhaust gas leaving the turbine housing (into exhaust) and pumping some
of it back into the turbine. Like recycling exhaust gases through the
turbine housing. I wonder what that would be like?

G.

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