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5yearplan:
What you actually suggest would not really eliminate lag. For starters, lets call lag the time an engine takes to make boost (I know I'm twisting it a little but stay with me)......I will have boost from about 1500rpm with the roots supercharger....with the additional bonus of greater mass flow through the engine due to the charging from the supercharger. This will infact help to make my relatively large turbo (not the one in the photo, but a GT3071R) spool up as though the engine were a larger displacment engine.
OK, so perhaps you were refering to the schrgr helping to spool the turbo as it passes through the intake....it really doesn't, the blades are not designed to deliver shaft power, the turbine blades are, but intake is not. You can do it...theres plenty of tractor pull vehicles with series turbo chargers, but its not for spooling, its for peak boost.
In fact, I really dont mind too much how much lag the turbo has....except for one reason, I want good transient response of the turbo and heres why:
1500 to 4500 - supercharger makes 12psi
3500 to 4500 - turbo will prob make around 10psi - total=22psi
At 4500 supercharger ius disengaged, and heres the trick in my opinion, the turbo has to replace that 10psi as quickly as possible, or it will appear as though the engine has lost power momentarily. This is why I have chosen a roller bearing turbo, and this is why I have a rather special bypass valve (thats my little secret for now...cuase its not flushed out totally yet)
So good question, but I am convinced this is the better way in my case to boost the engine. Its a packaging thing as well, theres more room on the lhs for intake etc.
And my final challenge is this....if it was good enough for lancia delta S4 groupB, Mazda March and the golf, then it's good enough for me :-)...and Ican tell you, the Lancia delta s4 used a BIG turbo...try 700+hp
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