turbo comparison...

[auditude at cox.net]

I offer no offense either Bernard. :-)

I would tend to give Ned a great deal of credit for knowing his stuff.  I saw some posts somewhere where
people wrote "Ned is God", so some are impressed.

Unless I had some evidence that was opposite Neds statements (like what the K means), I would be
hesitant to disagree.  It didn't read like he was asking. :-)  You have some IA stuff, so these are probably
honest customer questions which is totally fine.

I'm far from a turbo expert, but I have picked up some of the terms from Maximum Boost by Corky Bell,
and from the internet (the authority, right?).  I recommend that book, it's pretty good and easy to read.

I'm gonna share my ignorance a bit and post what I think is going on, so that others may correct me.  You
guys and gals are the technical folks I've got to bounce this off of.  I'll type some big generalizations, I
know more parts of the turbos can be manipulated like blade profile and stuff.

Although one might describe both halves of a turbo as turbines, I believe the hot side is "named" the
turbine, and the cold side is named the compressor.  My understanding is that the only thing the turbine
does is spin the compressor (hopefully) within a range of intended rpms.  In other words, the hot side is
matched to the engine so to speak, and you can "hang" different cold sides on it to mess with the boost
characteristics.  Hot side mods are only necessary to match up with the resultant output of the motor, I
think.

The size of the turbine affects how much air can be flowed through the turbo, but the blades can be
clipped to make the turbo act like it has a larger turbine (flow more exhaust).  This is at the expense of
boost onset rpm, but necessary when you are pushing lots of exhaust out of the motor.

Too small of a turbine will create more backpressure than necessary, and too large of one will raise the
rpm point that boost begins being produced.  I hesitate to call it boost lag, since I think that is something
else.  Perhaps it is the delay of producing "more" boost, once "any" boost is being produced at all.  Like,
once the turbine is spinning at the rpm at which it become effective, the extra time it takes for boost to
build up on the compressor side is boost lag?

Looking only at Ned's text without any other source of info, one could see that the compressor has both
an exducer and an inducer.  "In" and "ex" would seem to indicate that the air goes in the inducer and out
the exducer.  Inhale, exhale, etc.

Ned wrote exducer "from" the turbine, so that also suggests the gases are going out of that end.  One
might infer that since the hot side has both both an inducer and an exducer, that the cold side probably
does too.  They are just like mirror images of each other in a way.

Neds explanation of the RS2 makes it seem a lot less than a K25 that I might have previously believed.
That makes sense, since most view it as an upgrade from a K26.  I'm starting to be interested in an RS2
turbo, although I am very curious to seem some back-to-back comparisons of it to some hybrid turbos.
While I'm dreaming of comparisons, I'd like to see the hybrids compared both with and without ball
bearings.  We need a "consumer reports" for the q-list.

Well, I don't know/think/believe anything else, so I'll stop typing.
I did notice that this RS2 turbo analysis differs factually from another that I read here, IIRC.

It's great to see Ned posting here, btw.

Later,

Ken

Bernard Littau bernardl at acumenassociates.com wrote:
>
> Hi Ned,
>
> I am just looking to get my facts straight, no offense intended...
>
> > The K numbers refer to the turbine side
>
> There are two turbines on a "turbo".  I assume you mean the hot side
> is referred to by the "K" number, although I can't reconcile that with
> what is below.  Personally, I think the K24 designation of the RS2
> turbo was picked by random chance.  It was a toss up between a K24 and
> a K26, and none of the Germans like Javad's idea of a K25 :-)
>
> > The RS2 turbo IS a K24 with special K26 compressor housing. . .
>
> Yes, the part number for the RS2 turbo starts with K24, as do at least
> a half dozen other turbos from KKK.
>
> >
> > How is the RS2 turbo different from the "stock" K24?
> >
> >      Larger shaft for greater high rpm stability
> >      Larger bearings
> >      Larger compressor
> >         Same exducer diameter as "stock" K26
> >         Inducer is larger than both "stock" K24 & K26
> >            So "stock" K26 has its own built in restrictor
> >            "Stock" K24 does not have enough metal to bore out.
> >         Before the RS2 turbo tuners would sleeve a K26 compressor
> >         and then machine it larger
> >      Larger exducer from the turbine
> >         More lag
> >            That is why we offer a special model
> >            with an exducer between the two.
>
> I am a hot side/cold side student :-)  I am assuming that the inducer
> is the cold side and the exducer is the hot side?
>
> Thanks,
>
> Bernard Littau
> Woodinville, WA
> '88 5ktq IA Stage III-ish ECU and IA RS2-ish Turbo
>