03-11-2015, 11:23 AM
No means to rain on your parade - whilst what you've proposed will "work" - you need to think about transient conditions and what happens then, you're thinking in overall pressure, you need to consider what happens when you put 5lbs of boost infront of a smaller turbocharger, then suddenly take it away - and put it down the inlet instead - what does that do to the manifold pressure, also what does that do to the smaller turbochargers compressor efficiency, since now the operating conditions are totally different...
There's really no need for the check valve you have in your setup - you aren't moving anything like enough air to require them. You'll quickly realise that as soon as you open it, the pressure will suddenly drop (read up about the compound effect), you might as well go full compound, since soon as the big turbo spools up, the pressure ratio will drop across the smaller turbo and therefore flow rate will increase - removing the need for the valve - remember the smaller turbo is now not producing much pressure, merely flowing the air that the larger turbo has compressed above ambient - you just need to control the exhaust gas flow across the small and large turbos well. Long as you set your wastegates up correctly (you'll probably want to do this with some electronics)
Refer to diagram below for proper compound setup:
![[Image: tts4.jpg]](http://mkiv.supras.org.nz/images/articles/tts4.jpg)
Your limiting factor is not gaining more inlet pressure, since you can't use it realistically - rather spool capability - you might be wiser to use a modern BorgWarner EFR/Garrett GTX or similar with a appropriately sized turbine housing which would outperform a compound setup, cost similar and be more reliable under transient conditions. You can't shoot for insanely high inlet pressure without serious problems with knock, unless you're running on super dooper race fuel... An EFR has such a WIDE compressor map, you'll realistically be able to get a big turbo to spool fast, not surge *AND* provide a crapload of air at high RPMs.
Compound setups like you're suggesting are GENERALLY used on high power diesel setups, where 5-6bar boost is required - you can't realistically use more than about 25lbs without serious drops in compression and different designs of cylinder head which are better for combatting knock.
There's really no need for the check valve you have in your setup - you aren't moving anything like enough air to require them. You'll quickly realise that as soon as you open it, the pressure will suddenly drop (read up about the compound effect), you might as well go full compound, since soon as the big turbo spools up, the pressure ratio will drop across the smaller turbo and therefore flow rate will increase - removing the need for the valve - remember the smaller turbo is now not producing much pressure, merely flowing the air that the larger turbo has compressed above ambient - you just need to control the exhaust gas flow across the small and large turbos well. Long as you set your wastegates up correctly (you'll probably want to do this with some electronics)
Refer to diagram below for proper compound setup:
Your limiting factor is not gaining more inlet pressure, since you can't use it realistically - rather spool capability - you might be wiser to use a modern BorgWarner EFR/Garrett GTX or similar with a appropriately sized turbine housing which would outperform a compound setup, cost similar and be more reliable under transient conditions. You can't shoot for insanely high inlet pressure without serious problems with knock, unless you're running on super dooper race fuel... An EFR has such a WIDE compressor map, you'll realistically be able to get a big turbo to spool fast, not surge *AND* provide a crapload of air at high RPMs.
Compound setups like you're suggesting are GENERALLY used on high power diesel setups, where 5-6bar boost is required - you can't realistically use more than about 25lbs without serious drops in compression and different designs of cylinder head which are better for combatting knock.
