I've got a vf27 I was going to do this with long ago, never ran it though, kinda gave up on trying to get tiny turbos to live before it got tried outI think using this Turbo as LP stage and a small wastegate turbo for HP stage could yield good results. With a bypass for both turbine and compressor controlled with a boost controller of the boost differantial of both stages(just the boost of HP turbo) would make programming simpler and also avoid the need for interstage cooling as it's just compound at lower rpms. Is this a good idea? Are there even good small turbos on the market to allow low rpm spool on a 1.9tdi?
they were available used for cheap back then, dunno about now. Came off ebay.co-uk for under 150 bucks...
anyways, if you take your idea and simplify it further to a couple stupid wastegated turbos, you've got the set off the bmw "M57D30TÜTOP" engine, which includes all the bypass valving already assembled
ETA: https://www.ebay.com/itm/165189856584? they got more expensive than they used to be...
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