In reply to alfadriver :
I wish I could find it! Don't know if it was in the now defunct Allpar website, or from a paper magazine, but during the development of the Chrysler "B" engine, they had one on a dyno doing some manner of stress testing, with 60psi of shop air on the carbs inlet!
I don't know what is more impressive: 60psi boost in the 50s, or an air compressor setup that can feed a medium sized big-block 60psi at full throttle.
Tuning won't be hard with a screw/roots with tb pre sc and post turbo. As long as you don't want to clutch/bypass the sc at least.
I'm thinking of situations like part throttle, where the turbo might be spooling up and adding pressure pre-throttle, which would be different backpressure wise from the same situation with the turbo dormant and the same manifold pressure.
I know my Volvo does an end run around this kind of effect and it is not even twin charged: it has a pressure sensor not in the intake manifold but the charge pipe pre-throttle, so in effect it runs alpha-N with a boost pressure modifier. Now, the fascinating part to this is that Autometer makes a device called a Dash Control that hijacks the instrument cluster to display any data available on the high speed CAN. It can display "boost pressure" but this is not manifold pressure, it is charge pipe pressure. I do have a boost gauge that works "normally", showing pressure in the intake manifold. So, I can see pre- and post-throttle body pressure. I can sit there crusing at just under atmospheric manifold pressure and the Dash Control is showing 6psi "boost" from the turbo.
Really neat stuff!
And I am reminded of the Audi WK engine that I had, that people swear up and down was not rigged this way: It was a non intercooled, draw through turbo setup. it had an external wastegate per standard Audi practice, but to keep the turbo from running away at part throttle, the wastegate was controlled by exhaust manifold pressure!
I don't think that would matter at least tuning speed density. I can see why you may benefit from other sensors when using maf. I wouldn't think emap would be that useful with the turbo sizing on the larger side to get the power band more toward the top end to complement the sc.
In reply to Paul_VR6 (Forum Supporter) :
As I understand it, just to make the math simple (and the math is not simple, because of various volumetric efficiencies involved), let's say you have a 2 liter engine with 7psi boost, so the engine and supercharger are flowing air like a 3 liter engine. So you size your turbo to be like a 3 liter engine making 15psi boost or whatever.
This would be an extremely large turbo... for a 2l. But that is the point. If you used a small turbo, there would be no benefit.
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