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Thierry25 Thierry25 is offline
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Join Date: Feb 2009
Location: FRANCE (Besanšon)
Posts: 310
Originally Posted by 911st View Post
I am starting to wonder if BW/Porsche was extreamly effective in how they disigned the K27-7200.

This is just a gut feel on my part. I am thinking the compressor wheels and turbine are nearly perfictly sized for a CIS 930 of modest tune.

And that both the turbine and compressor sides were just big enought and both stall at the same time.

The 7006 has bassicaly the same size compressor wheel but with its larger hot side makes more HP.

With the HF's and K29 quick spools -- a larger compressor wheel is added. This allows more air flow to be passed before the hot side starts to stall again.

Part of the reason a good wast gate circut is needed with these turbos or boost creep 'may' become an issue.

Years ago I bumped in to a pretty good turbo guy that was working on development a more efficient turbine wheel for the 7200. He believed there was opportunity to make more HP with the 7200 and keep the early spool with a more modern wheel. Thus, he seemed to think the compressor wheel was pretty good and the issue was more on the hot side.

Just a thought.

I know this is not the answer as the compressor map for the 7200 is limited.
Oh very glad, I just got an answer from BOB. The compact K29 is now available

Actually the discussion with Bob was very interesting. According to this expert, the main limitation ( the wall) is the section (11 sqcm) of the hot side input. In fact, beyound a certain exhaust flow volume, the turbine wheel can not accept the flow speed and can be damaged ( turbine chock).

So whatever you use on the cold side, the hot side is limited be the exhaust flow speed...... thus it can not be over a given flow rate. From what I understood , this is is the ultimate limit of the turbo. From this fact, it seems impossible to expect more than 440-460 CV from a stock (11sqcm) K27-7200 hot side body . It seems possible to get some benefit by using a K27-7006 hot side.... but as the hot side input section is very similar to the K27-7200, the rule of the flow speed is the same. So yes it can be a good choice to use the K27-7006 hot side but it won't be a night & day difference.

Now, having said that, The K27-7200 in it standard version doesn't reach this exhaust flow limit first. In fact, there is some room to play on the cold side. So it is possible to increase (a little bit) the compressor side capability in order to get a bit more intake flow without to bring the turbine side in danger.

Is there anyone here who have a correct K27-7006 core for rebuild to sell ????
965 C2T / 1991 3.3 TURBO
Old 02-16-2010, 09:24 AM
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