RS2 Turbo with K26 hot side advice needed

[orsum]

I am looking to buy an original RS2 Turbo but it has had a small mod they recently changed the hot side to a K26 because of cracks. It has been rebuilt and has not run since rebuild.

This is what the owner said.

Regarding turbo the spool up time would be very similar to stock which should see max boost just above 3000 rpm. If I am not mistaken the stock RS2 outlet OD is 55mm and this K26 housing is 57mm so not really much of a difference spool up/ power will be very similar to stock.

Should I be concerned with its performance? Will it perform equal to or better than the standard RS2.

I will also be buying the original RS2 manifold from him but it has been welded before. It is presently showing no signs of cracking.

Regarding software for this turbo on my S2 ABY will it need anything special? Apart for the normal upgrade 3 bar mod etc.

New injectors and DP will also be fitted.

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[SteveH]

Ask the seller whether the K26 hotside is a number 6 or 8, Without running the turbo you can't be sure what it will spool like. If it has a number 8 hotside it will spool later but will breather better at the top end of the rev range. I run a KX500 26/27 hybrid and I know it has a number 8 hotside with 55mm OD from memory. It spools later than an RS2 unit.

[orsum]

He is sending pics tonight will check

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[twoqu]

Be careful here!
Obviously if somebody has changed the turbine housing for a non RS2 one, its no longer an RS2 turbo!
I guess its going to depend on what exactly has been done. Basically the turbine housing and the turbine wheel are matched in size. Whilst its physically possible to fit a larger one in terms of minor diameter, having a large gap around the turbine is not going to enhance performance.
They may have fited both the turbine housing and turbine shaft of a K26 to the RS2 compressor parts, essentially making an hybrid. As the turbine is larger it will obviously not have the exact same characteristics of an RS2 turbo. It would also mean that most of the desirable RS2 bits have dissappeared!
In theory that should make it spool later. Not sure I have seen any data on that combo but would be interested to see what effects it has. Not all hybrids are successful.
Seem to recall that the std RS2 has an exit of nearer 54mm. A couple of mm doesen't sound a lot, but in turbo's its quite significant. Sounds like Steve's one is built around the Porsche 944 shaft and turbine which I believe does have the 55mm outlet and indeed the #8 housing. The Audi K26 had variants with the 56mm outlet.

[twoqu]

Just for reference an RS2 has a turbine outlet of 54.2mm whilst an Audi K26 has 56mm. I have measured those myself!
There are of course other K26 variants, Porsche beng one. I found some Porsche measurements but cannot vouch for their accuracy. Both indicates that the turbine outlet was 1.5mm larger in diameter than the turbine shaft minor diameter.
So you can see the issue I hope.

[orsum]

This issue is clear right from the off its not an original RS2 turbo it had cracks in the hot side that requires a change.

The real issue is how far off the RS2 performance will it be and should I take it.

I have no doubt about the condition of the turbo or the person selling it I am only concerned about how this will perform when measured against an original RS2.

I will give more info as I get it.

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[Quattronaut]

The turbine wheel that is used is probably the K26 contour 1, whis has got nearly the same capacity as the RS2 one, but is more laggy due to it´s bigger inlet diameter.
So the turbo will boost a little later, and spool up itself should be a bit slower. RS2 original one will work better. Overall reachable power should be nearly the same.

I think, it´s a "6" housing- the "8" housings are very rare, and quite expensive. To check that, watch at the inside of the turbine inlet, there is a 6 or 8 casted into the material- but watch very accurate, those numbers are casted in poor quality :-)

Sure, that the seller didn´t touch the compressor side?

[orsum]

A little bit more info on the turbo from the owner.

On the compressor (cold side) it is completely stock RS2 with housing part number 5326-101-5160 .
Inlet ID = 48mm
Outlet ID = 40,5mm
The compressor wheel is stock RS2 .

On the turbine (Hot side) things get a little more difficult to read but it’s either 5326-101-6367 or 5367 but after a Google search I had no hits on 5367 so has to be 6367.
Inlet ID = 48.49mm but this seems be standard as all my Audi KKK’s seem to share this dimension.

Outlet ID = 56..57mm as close as i can measure without a vernier but i know that the stock K26 RS2 ID = 54..55mm.

He also said he is waiting on Turbo company to give him the Turbine wheel dimensions they fitted.

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[orsum]

The owner has found the number and it’s a #6 he sent me photos after a light sanding and it’s quite clear.

I am still waiting for turbine data.

Is the #6 housing acceptable with the rest of the RS2 turbo parts providing the turbine is ok. Will this work well with a good software upgrade?

What power would be expected

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[adam g]

The RS2 turbo has a #6 turbine housing as standard so it's totally acceptable.

Sent from my C5303 using Tapatalk

[orsum]

Is the RS2 #6 housing is different to the #6 K26 housing? And if there is how much different is ther in performance.

I do not wish to have any issues with a hybrid RS2 turbo is there any way to make sure you do not buy a lemon.

Is it the impeller inside and the number of blades, size of the openings or the physical size that matters?

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[adam g]

Housings are machined to suit the physical size of the wheel, inducer/exducer, so an RS2 housing will be different to K26.

Sent from my C5303 using Tapatalk

[Quattronaut]

I already mentioned above, but here a bit more accurate:

Is the RS2 #6 housing is different to the #6 K26 housing?

For the K24/7200 (RS2 turbo), KKK used K26 housing and rotor workpieces, and machined wheel and housing inside to K24 specifications. So RS2 charger has K26´s 10mm shaft and housing, but inside there´s K24 wheel with 59mm ID. You can fit a normal K26 rotor into a RS2 charger by machining the housing inside from K24 59mm ID to K26 64,4mm ID, but it´s not possible to fit the RS2 rotor into a normal K26 housing- machining from 64,4 to 59mm won´t work

Is it the impeller inside and the number of blades, size of the openings or the physical size that matters

Number of blades not. Still today in TT RS 2,5L KKK uses the same geometry turbine wheels.
Main thing for capacity of turbine wheels is outlet diameter. Main thing for "spool up speed" and "boost at rpm" is weight and size. Inside one "turbine family", e.g. here the K26, there are different contours (or shapes, don´t know how you call it in english) that lead to different outlet diameters and within that to different capacities.

And if there is how much different is ther in performance

Since RS2 turbine is contour 2, it´s quite capable. Most (I guess 90% or more) of the K26 turbine wheels are contour 1, and in fact those have nearly the same capacity (difference in exduce area around 4%) as the K24/7200 turbine has. But the K26 are 30% heavier, and moment of inertia is higher due to the bigger ID of the K26.
Both turbine wheels can do up to 400-420hp (under special circumstances the K24/7200 can produce even a bit more power than the K26 c1). But K26 will be more laggy and boost later.

What power would be expected

The limitting thing here is the compressor side, that is able to do up to 360ps.

[orsum]

This is what I have been told are the measurements off the turbo I am buying.

K26 #6 Hot side 64.3 and 54.4mm
K26 Shaft and impeller

With the

K24 7200 Cold side
Out 40.5mm
In 48.5

So the only difference is the hot side casting, turbine shaft and impeller.

The RS2 = 65 and 53mm or so I am told.

Not than much difference or is it ?????????

Should I ask for any more details or are the Turbo gurus happy this will be ok for my RS2 conversion and software upgrade.

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