Quote:
Originally Posted by SYT_Shadow
That's the beauty of superchargers: zero lag. As they're driven by the crank itself there's no need to wait until there's increased exhaust pressure to start getting some boost.
In this case you have the additional advantage of having a centrifugal blower, which conserves the S65's extremely linear power delivery and simply gives you more of the good stuff at all times.
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No, it gives you more of the good stuff only when engine rpm are sufficient for the centrifugal to produce positive pressure. A centrifugal supercharger produces peak boost only at peak rpm, and you are never there for long. The boost curve is actually exponential, with little boost produced in the first half of the engine rpm and more boost produced in the second half of the engine rom. Roughly, the centrifugal will produce the square root of peak boost at half peak engine rpm. In other words, the centrifugal that makes 7.5 psi at 8400 rpm makes 2.75 psi at 4200 rpm.
On the other hand, 2.75 psi does add significant power and on these high revving motors, you are often driving at 4000 rpm and up. And the metered boost of the centrifugal does match up well with the metered power of the low torque high rpm S65 to produce a gradual, straight line power delivery.
A nicely done turbo system will spank a centrifugal because it will produce full boost in the midrange rather than the square root of full boost. Since that is the engine's natural torque peak, torque is way higher with a turbo.
I first supercharged and then turbocharged my E36M3. Both systems were modded well past the typical stage 2 level. With the centrifugal, I made 16 psi peak boost at 7000 and about 4 psi at 3500 rpm, producing 463 rwhp and 368 lbs rwtq. With the turbo, I make 15 psi at 3100 rpm in 5th, 3300 rpm in 4th, 4000 rpm in 3rd, and wheelspin in 1st and 2nd before I hit 15 psi, and it makes around 500 rwhp and around 475 lbs rwtq.
With the turbo, I am not waiting around for the power to arrive like I used to wait with the centrifugal. The fun is not all in the top 1/3 of the rpm curve.