S2 & RS2 turbo comparison

[S2central.net]

Just made some quick measurements on the two turbine wheels here -

Both have a 'major' dimension (nearest centre bearing) of ~58mm

S2 turbine has a 'minor' dimension of ~44mm whereas the RS2 is ~52mm

The S2 hotside housing diameter is ~46mm against the RS2 diamater of ~54mm.

My measurements aren't exact... but it would appear that a turbine with a minor dimension of something in the region of 48mm would be a candidate for this small hybrid application.

I'll get professional advice on the cracks in my S2 hotside before suitable machine operations to replace the two hacked studs and increase the turbine hole to ~50mm.

I'll keep the RS2 compressor as it is and see how that one maps out... My guesstimate is about 320-330bhp with 98RON and an RS2 intercooler and I'm reasonably confident of less lag and quicker spool than RS2 - by nature of the smaller A/R and turbine wheel.

If it doesn't work out then I can always machine the housing bigger again to take the RS2 turbine wheel.

Paul

[twoqu]

Ok, That useful!
So it seems the turbine minors are in 2mm increments. The 48mm turbine is going to be the one all the German tuners used and the one I have. It is used with the 6.91 and possibly the Porsche 6.92 turbine housing as they have the same 50mm outlet. Being a pedant, I have measured it at 48.4mm!
If the shafts have the same major then that does seem to open the door for machining the K24 turbine out to the RS2 dimensions. Proberly just what KKK did!
So worst case sceanario is that you have a usuable RS2 turbo.
Pretty confident now that that it would be possible to graft the RS2 compressor side onto the K24 with modifications to the comp wheel. Whether this would make a good combination I'll leave to the experts!
Unfortunately my "consignment" hasn't appeared. It would be interesting to see if the RS2 uses a 360degree thrust bearing and lht shaft.

[porkkis]

Std s2 turbo uses K16 bearings and has a shaft diameter of 5mm versus RS2 uses the K24/26 bearings and has the shaft diameter of 7mm.

The old Mercedes TD engine uses also K24 series turbo with the smaller K16 bearings. Probably there are some others too.

[twoqu]

Std s2 turbo uses K16 bearings and has a shaft diameter of 5mm versus RS2 uses the K24/26 bearings and has the shaft diameter of 7mm.

The old Mercedes TD engine uses also K24 series turbo with the smaller K16 bearings. Probably there are some others too.

Hi!
Initially I thought the K24 used a smaller shaft. I have looked at a company that supplies turbo spares to the remanufacturing industry and they list the same bearing for the K24/26/27! They talk about the "large" K27 housing. So as the K24 uses the same bearing housing I am assuming the shaft diameter is the same. What I suspect is that the shaft has a narrower diameter and the comp wheel i/d and the nut are smaller too!
We really need to dismantle a dead one if we want proof.
I'll double check the info.

Yep! they state: Two styles of K24 turbo - small K14 style and large K27 style bearing housings. The cross reference with the KKK part number is the same on both the K24 and K26.

[S2central.net]

Here's a quick pic of the two turbine wheels. RS2 on the left...

[S2central.net]

I dunno about shaft diameters and the like right now. My plan with the small hybrid is currently to run with the RS2 cold-side and compressor wheel - attached to the centre assembly.

I'll use the S2 hotside housing and have it bored out to accomodate the 48mm turbine wheel.

I'll keep the 52mm RS2 turbine wheel for a rainy day - perhaps to try with another modified S2 hotside housing.


A totally different project would be to modify the S2 cold side in order to accomodate a larger compressor wheel - I'm not in the mind for doing that at the moment... Seeing as there would be no trusted compressor map to work from... and using the K26 sized coldside housing from the RS2 will give superior thermal efficiency anyway.

I'd like to disassemble both turbos further but this is new territory for me and I'd hate to damage something trying to bodge a means of removing the wheels. It was scarey enough persuading the hotside housings to separate from the centre with a hammer !!!


Paul

[porkkis]

Turbine wheel and shaft is one part. You have to select your center section depending on the shaft thickness.

Where can this 48mm turbine wheel (+shaft) be found?

I'm not quite sure will this 48/48 turbo be any good. It'll just add back pressure and the potential of the compressor can't be used.

[Billman]

machine the K24 housing to fit the RS2 exhaust wheel. I think it will spool quiker but choke at the redline.

An RS2 performance with less lag

[S2central.net]

Turbine wheel and shaft is one part. You have to select your center section depending on the shaft thickness.

Where can this 48mm turbine wheel (+shaft) be found?

I'm not quite sure will this 48/48 turbo be any good. It'll just add back pressure and the potential of the compressor can't be used.

Didn't know the turbine wheel and shaft was one part !!!!

I have no clue where to find such a 48mm wheel yet - it might be in the KKK catalog along with info about diameter - though we don't yet know is the S2 and RS2 centre sections are different because of this.

I share your concerns about the 48mm wheel perhaps not being able to make full use of the compressor, but my thinking is that I'm not aiming to stretch the compressor to the max, but being able to run 1.5bar boost from 3000 to 5500 (with less lag than RS2 and ultimately a lot less max power) would make for a nice fat n flat torque profile... Ultimate power on the redline is less important to me.

That and if I don't try this myself - how else will we find the truth !!!

Paul

[porkkis]

Sure we do, but you don't believe until you see it with your own eyes

though we don't yet know is the S2 and RS2 centre sections are different because of this.

Paul

[twoqu]

Didn't know the turbine wheel and shaft was one part !!!!

I have no clue where to find such a 48mm wheel yet - it might be in the KKK catalog along with info about diameter - though we don't yet know is the S2 and RS2 centre sections are different because of this.

I share your concerns about the 48mm wheel perhaps not being able to make full use of the compressor, but my thinking is that I'm not aiming to stretch the compressor to the max, but being able to run 1.5bar boost from 3000 to 5500 (with less lag than RS2 and ultimately a lot less max power) would make for a nice fat n flat torque profile... Ultimate power on the redline is less important to me.

That and if I don't try this myself - how else will we find the truth !!!

Paul

Well it wasn't initially. They are friction welded together!
Without wishing to state the obvious. Find either an Audi 6.91(early 200t) or a Porsche 6.92 turbo (early 944t) and you should have a turbine and shaft donor.
Fortunately, or rather unfortunately, I seem to have this hotside as it was part of a hybrid turbo K24/26 AET built. Strangly it is all K26! The shaft is like new and it disgraced itself pretty early in its life. The comp wheel touched the housing. Although the comp housing cleaned up, the comp wheel was knacked. As it was relatively fresh it was easy to dismantle. Appears that one of the circlips holding the bearing was omitted from the centre housing. Whether that was the cause of the problem or not I can't comment. Would have been way out of any warantee/guarantee by the time I got it any way.
So effectively I am looking at doing this the other way round. I believe I have the correct hotside. I am just waiting for the delivery of the cold side from an RS2 from another forum member. As its already damaged I'm not too concerned about how I dismantle it providing the cold side comes off.
I have tried to dismantle these before and the difficultly is in removing the comp wheel from the shaft. Once this obstacle is overcome its a pretty simple thing to take apart. Problems in reassembly are obtaining rebuild kits and the balancing. Most firms only sell kits to the trade.
So I might be in a beter position to answer some of the questions, providing the other turbo turns up. Besides I'm doing the planet a favour by making one good turbo out of two dead ones!

[S2central.net]

Petit bump...

RObin's more recent related thread prompted my memory on something else...

I was comparing some internal dimensions on the S2 and RS2 turbine scrolls. It is possible to see that the RS2 is slightly larger in terms of the gap that is visible on the internal edge.

I'm going to proceed with machining my spare S2 turbine housing for duty on the RS2 turbo. I'm not going to bother with the hassle of locating 'small hybrid' wheels but I will investigate the cost of upgrading to a 360 degree thrust bearing... and getting the moving parts dynamically balanced by the turbo fairies.

Paul

[S2central.net]

Meant to add - the purpose of this exercise is to get close to RS2 performance levels with quicker spool and less lag than an official RS2 hotside.

Apparently the S2 hotside has a slightly lower A/R ratio which means it will produce less maximum power than the RS2 item - but it should be more responsive.

To heck with it - I'll have to get some bigger fuel injectors to do this properly.

I already have a plastic pressure pipe and RS2 IC to bolt up - each reducing air temps and making more power. I need to save the pennies for the RS2 EM to make it worth the hassle... and that will mean removing the head... and I haven't bought new coil packs yet... or a new lambda probe... or knock sensors.

Oh I hate these cars sometimes - actually thats not quite true - what I hate is not having enough spare time to give the car the attention it needs to get into tiptop condition.

Paul

[S2central.net]

Then there's VG oil seals, the umpteen hours needed to spruce up the head, get the valves reground, get a new gasket set, fit ARP head studs, change all the belts and associated parafinalia... Ugggh the thought is a bit daunting right now.

Time machine anyone ?



PAul

[Chris M]

It'll all be worth it in the end Paul