S2 & RS2 turbo comparison

[S2central.net]

Sorry if this thread stomps over some well trodden territory, but seeing as I finally got some time to compare an S2 turbo and RS2 turbo side by side on the bench last weekend its only right and proper that I share this.

Apologies if this isn't news to everyone - but hey ...

The S2 and RS2 hot side housing is the same as far as I can tell - only exception being of course that the RS2 hotside is machined to accept the larger turbine wheel of the RS2. This surprised me as I always thought the RS2 hotside housing was physically larger than S2.

The centre section looks identical as well (which I did expect) - but I seem to recall reading somewhere that the RS2 application uses a thicker shaft (connecting the wheels) and therefore a different bearing. Dunno about that yet but its believable.

The cold-side (compressor) is of course where the differences are rather obvious. The RS2 housing is visibly bigger than S2 and of course the compressor wheel is different.

'So what' I hear you say -

Well what I think this means is that you could take the healthy hot-side housing from an S2 turbo and have it machined to the dimensions needed for the RS2 application. Pretty handy for me sitting with an RS2 turbo that has an alleged crack in the hot-side housing, and I have a spare S2 turbo to play with... Maybe sourcing a hotside will be easy after all


Talking of cracks - anybody know of a UK specialist that can perform reliable crack testing on something like a turbo housing ?

There is a lot of casting flash on the internals of these hot-sides - I'd like to get the turbos stripped and crack tested before polishing up the internals as best I can - just on the hotsides.

Photos and dimensional info to come in due course....


Paul

[Chris M]

Interesting info Paul You going down the RS2 route or still playing with the idea of a K24 Nugent Hybrid??

Cheers,
Chris

[Mihnea]

I don't know honestly if this can really be done or not. All I know is that the stock S2 hot side is really restrictive at anything past 300 crank HP and backpressure there goes through the roof when you try to up the boost so you can make anything over 300.

Just a thought...

Mihnea

Sorry if this thread stomps over some well trodden territory, but seeing as I finally got some time to compare an S2 turbo and RS2 turbo side by side on the bench last weekend its only right and proper that I share this.

Apologies if this isn't news to everyone - but hey ...

The S2 and RS2 hot side housing is the same as far as I can tell - only exception being of course that the RS2 hotside is machined to accept the larger turbine wheel of the RS2. This surprised me as I always thought the RS2 hotside housing was physically larger than S2.

The centre section looks identical as well (which I did expect) - but I seem to recall reading somewhere that the RS2 application uses a thicker shaft (connecting the wheels) and therefore a different bearing. Dunno about that yet but its believable.

The cold-side (compressor) is of course where the differences are rather obvious. The RS2 housing is visibly bigger than S2 and of course the compressor wheel is different.

'So what' I hear you say -

Well what I think this means is that you could take the healthy hot-side housing from an S2 turbo and have it machined to the dimensions needed for the RS2 application. Pretty handy for me sitting with an RS2 turbo that has an alleged crack in the hot-side housing, and I have a spare S2 turbo to play with... Maybe sourcing a hotside will be easy after all


Talking of cracks - anybody know of a UK specialist that can perform reliable crack testing on something like a turbo housing ?

There is a lot of casting flash on the internals of these hot-sides - I'd like to get the turbos stripped and crack tested before polishing up the internals as best I can - just on the hotsides.

Photos and dimensional info to come in due course....


Paul

[porkkis]

The turbine housings are not exactly the same. They're both #6, yes, but the s2 stock housing is 6.13 and rs2 housing is 6.12. AFAIK you can calculate the a/r from these simply by dividing the numbers:
s2 a/r = 6/13 ~ 0.46
rs2 a/r = 6/12 = 0.5
So machining the std housing for rs2 wheel doesn't make the housings the same.

The difference is not huge but still the 0.5 housing will flow better.

[S2central.net]

I'm just going in visual info here so far - I haven't measured anything yet...

I agree with Mihnea about the K24 limit being 300bhp but I *suspect* thats more about the turbine wheel size than anything else.

I'm keen on the idea of using the K24 hotside in the interests of science - modified to work with RS2 sized turbine. If the A/R is slightly lower then it should boost quicker than the RS2 item but will obviously not produce as much power as the RS2 item - unless the cold-side is of course the limiting factor (i dunno).

If I can get a reliable 320bhp & 550Nm with minimal lag on 95RON fuel then I'll be happy enough. That puts me on the limit of the S2 fuel injectors of course so I might have to invest in a 5bar FPR for extra headroom. Bosch motorsport pump is a given also...

Compare that to a typical maximum of 350bhp using 95RON on an official RS2 turbo, with the downside of more lag and more likelihood of using RS2 injectors and that is why the K24 hotside has appeal for me.


Paul

[S2central.net]

Does anyone here have KKK catalog ?

I'd like to see a list of all the turbine and compressor wheels available in the K24 and K26 family. The numbering scheme is kinda confusing... A number of websites tell me the KKK part numbers on compressor wheels - but turbine wheels are a bit more mysterious.


Paul

[91_S2]

The turbine housings are not exactly the same. They're both #6, yes, but the s2 stock housing is 6.13 and rs2 housing is 6.12. AFAIK you can calculate the a/r from these simply by dividing the numbers:
s2 a/r = 6/13 ~ 0.46
rs2 a/r = 6/12 = 0.5

That was an interesting bit of info. Gives some sense to the numbers.

[dan_b]

I'm just going in visual info here so far - I haven't measured anything yet...

I agree with Mihnea about the K24 limit being 300bhp but I *suspect* thats more about the turbine wheel size than anything else.

I'm keen on the idea of using the K24 hotside in the interests of science - modified to work with RS2 sized turbine. If the A/R is slightly lower then it should boost quicker than the RS2 item but will obviously not produce as much power as the RS2 item - unless the cold-side is of course the limiting factor (i dunno).

If I can get a reliable 320bhp & 550Nm with minimal lag on 95RON fuel then I'll be happy enough. That puts me on the limit of the S2 fuel injectors of course so I might have to invest in a 5bar FPR for extra headroom. Bosch motorsport pump is a given also...

Compare that to a typical maximum of 350bhp using 95RON on an official RS2 turbo, with the downside of more lag and more likelihood of using RS2 injectors and that is why the K24 hotside has appeal for me.


Paul

I liike your thinking here Paul - keep us updated of any progress you make

[Mihnea]

I definitely don't think an S2 will do 550Nm on 95 RON with stock injectors, nevermind 320 BHP. 320 BHP is the limit of the stock injectors on 98 RON, which is not even something that is currently available in the UK (after doing cars on and off in France and the UK, I can definitely swear that what's sold in the UK as 98 isn't 98), so 320 BHP on 95 RON is more of a dream than something else. The fuel alone will make you lose at least 20 to 30 BHP, the EGT's will be higher on 95 because of less timing and the injectors will be maxxing out well before 300 BHP IMHO.


HTH,

Mihnea

[caterpillar]

kkk turbos are called today borg warner i think: http://www.forcedinductions.com/productsborgwarner.htm
have looked for the kkk-katalog,but nope!!
and for IHI too....no!!

[dan_b]

Mihnea what's your view/ experience of the 99Ron fuel being sold at Tesco, is that what it says it is?

[Mihnea]

dan, all I can say is that it's definitely good ****!!!

[hiltoa]

[S2central.net]

I definitely don't think an S2 will do 550Nm on 95 RON with stock injectors, nevermind 320 BHP. 320 BHP is the limit of the stock injectors on 98 RON, which is not even something that is currently available in the UK (after doing cars on and off in France and the UK, I can definitely swear that what's sold in the UK as 98 isn't 98), so 320 BHP on 95 RON is more of a dream than something else. The fuel alone will make you lose at least 20 to 30 BHP, the EGT's will be higher on 95 because of less timing and the injectors will be maxxing out well before 300 BHP IMHO.


HTH,

Mihnea

Fair point on the fuel actually... Maybe I'm trying too hard to avoid a fuel injector upgrade, but I'm hoping that running at 5bar fuel pressure will give me the headroom I need. I'll do some more calculations and soul searching. Maybe its not enough for my target and I should just assume I need the RS2 injectors after all.

I wish we 2nd class citizens on the Emerald Isle could get Tesco 99 juice but the nearest thing to decent fuel we get is BP Ultimate (which I don't like) at an alleged 97RON but with an unknown MON value (which I bet is rubbish). So I can't set targets on assumption of anything much better than plainold 95RON.

Sure I'd love to have a Toluene factory in the shed but thats not going to happen.

Paul

[S2central.net]

Just done the math based on ...

f1/f2 = sqrt (p1/p2)

Assuming f1 is 320cc at 4bar fuel pressure on the S2 injector, I get 357cc for the same injector at 5bar.

Using the rule of thumb of 1bhp per injector cc, I'm looking a theoretical capability of nearly 360bhp then - with 98RON or better fuel. Knock (no pun intended) 10% off that for rubbish 95RON fuel and I get 320bhp on this configuration.


Thats the theory as they say


Paul