Well I have finally got round to sorting the parts for Will's turbo upgrade, and think I'm there now... rebuild to start soon.
So here are some pictures of the original component parts and commentary.
The turbine was a standard spec T3, and from the picture working close to its thermal limit. This was known mainly from the back pressure on the engine, and hitting a choke flow at high rpm limiting the engine’s breathing capability. The compromise challenge is to reduce the back pressure, allow higher boost without generating excess heat, and retain fast spool response given Will’s main aim of hill climb motorsport. Plus the over arching requirement – keep cost down, so T3 plain bearing DIY rebuild technology is it.
As you can see nice colouration, but close to the edge. So having mulled things over, I have decided to keep to a T3 turbine, but a phase III version, still 11 blades, back cut, and larger tip height. This last aspect is important, as one of the olde golden rules is to keep the wheel diameters between compressor and turbine less than 20% due to losses and compressor slip factor.
Old combo:
New combo:
Will’s original hybrid was one from some time back, and was setup with a T3 compressor 18% larger than turbine, and know compressor map. However looking at where Will is looking to go boost wise, the efficiency is down at 60% at best, so generating excess heat that has then got to be removed by limited inter-cooling as we all know. So an upgrade on the compressor is essential as well, noting trying to keep the inertia (mainly diameter) and overall mass down.
Both old and new turbine shafts weigh in at 166g so no detrimental impact there, and new setup, again works on the <20% rule, coming in at 18%, and plotting the desired pressure / rpm mass flow points on the new compressor map comes in at 76% efficiency for the same conditions. The old compressor weighs 49.1g, and the new 65.9g, but this can’t be helped, but some what offset by the larger tip height of the new turbine providing an increased ability to extract energy.
So new combo above and old below to be balanced and then assembled: