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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
In the past putting a K29 compressor wheel in a hybrid K27 frame was the best option for a motor that was going to make in the 400hp range. The stock LDZ just could not support over 300hp at any level of efficiency. The larger compressor wheel could move more air and heats the intake air less when doing it so more air and fuel can be packed into the motor and the ignition can be operated at a more ideal setting.

The K27-7006 and K27-7200 worked very well into the 360+hp range with modest sized compressor wheels. The 7006 has a larger hot side and makes better track HP. The 7200 has a smaller hot side and comes in faster.

Most of the newer K27 hybrid turbos do not use the old K29 compressor wheels anymore as there are a lot of other choices that might fit better, have less weight to them, and run more efficiently. They are often called HF or K29 quick spool turbos depending on who you get them from. Most are based on the small hot side K27-7200 which seems to hit a wall as to how much exhaust it can flow no mater what size compressor wheel you put with it.

The trend dose seem to be toward larger compressor wheel turbos with smaller turbine hot sides. This seems to make for a turbo that comes on earlier because of its smaller turbine and also can support more HP efficiently with its larger air flow potential.

This works well on a street oriented car. Just make sure you have the wastgate capacity to bled the increased volume so the boost dose not creep over your goal.

Also, thinking of how you can get the WG side to flow well just like we do at other parts of the exhaust system would probably be a good idea.

However, if you are building a track car, going to a larger hot side can reduce pressure in the headers add more HP to the part of the 4000-7000rpm power curve you would be using on the track. The cost is boost onset and full boost points being about 300rpm or so later.

Just a note, moving from say 60% to 70% efficiency is about a 17% increase in efficiency which is pretty significant.
Old 03-22-2010, 10:17 PM
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