Machined the front cover till it just touched. Then used fine wet and dry where it scraped the marker pen I put on it on my olde lathe.. I used to build these things. Keep repeating untill as much of the front cover and compressor is almost touching as possible. Then give it one more go, thats the running clearance

The biggest difference between a wren mw54 and a supersport is the running clearance and its also why they dont sell it as a self assembly kit.

If it helps the supersport it will help the JJ too. There was loads of clearance on mine, and once set up a bit tighter it runs cooler and better especially at startup. But I dont know about thrust because I didnt measure that before... But if the compressor is less "leaky" then it becomes more efficient.