<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Induction Concepts:
As far as turbos spooling, if they are chosen correctly, they make power down low, but I consider 'down low' to be in the 2500-3000rpm range. Even from idle, with properly sized turbos, it is a very small frame of time between then and full boost at 3000rpms. Of course if you have 1500hp worth of turbo(s), its not going to spool at 2500-3000rpms, but if you are looking for that kind of power level, that is usually a non-issue.
And yes, you are correct, I was talking about a torque curve for a turbo after it has spooled. Many dynos don't register properly below 3000rpms anyway. On the street, a system setup for boost at 2500-3000rpms is about right, because thats right where your engine spends a lot of its time so you're already in the spool range or very close to it. I mean when you floor it, how long does it take to go from 1500rpms to 2500rpms, not long. It all comes down to the power level and purpose desired for the application. You can make a setup that will spool right off idle, but don't expect 800hp out of it.
Anyway, as I said, I was only trying to help the person asking, not turn this into a turbo thread or supercharger debate. </div></BLOCKQUOTE>
Actually I do have to agree with everything you said above but I'd call 2500-3000 rpm, on a 6-6500 rpm motor, more mid range. And obviously a turbo spools much quicker under a real load than on a Dynojet but, for better or worse, Dynojet readings seem to be the de facto standard for measuring hp.
The nice thing about any positive displacement supercharger, Roots or twin-screw, is near instant maximum boost. From just off-idle to well into the mid-range (and higher with a twin-screw) the + displacement will provide constant maximum boost. A good thing for a 6,400 lb. brick. Now if it were a 3,400 lb. car with a smaller, faster revving motor and you could get it rolling with significantly less torque I'd go with a turbo.
I'm impressed with some of the stuff that Livernois is doing with turbos and their Escalade definitely runs but in the video you can hear him stalling it up to spool the turbo before launching. Here's a dyno graph of a Silverado with a turbo motor (a T-76 Q-trim) and, while an impressive gain of 125 ft.-lbs. over the stock motor at 3500 rpm the turbo isn't fully spooled until it's pushing 4000 rpm.
A decent + displacement supercharger is going to produce that much torque at 2,000 rpm (my Lightning threw down 540 ft.-lbs. on the stock Eaton at 15 lbs. at 2,800 rpm and it was probably higher but I hadn't programmed it to lock-out the downshifts so I couldn't get readings from lower in the rpm range).
So, picks your poison - either off-idle grunt with a + displacement supercharger or a top-end pull that doesn't stop with a turbo. It's all up to what you want to do with the vehicle.