Quote:
Originally Posted by Properstyle
It's not really a pd vs centri. The bore and stroke of a s65 is not designed to actually make tq down low. So you will
Never see that table top power band like you do on any other platform using a pd blower.
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It really is PD vs centrifugal. You are not understanding how either work and their respective boost curves. You cannot change centrifugal to make full boost at low rpm, apart from over spinning it and bleeding off boost at high rpm. Even a planetary gear drive centrifugal like ASA, Rotrex and HKS have the same centrifugal curve. They spin faster than the vortex so they reach the minimum centrifugal speed at which boost starts being created a little bit sooner. But it’s pretty minor. Study the AA Rotrex 600 rwhp dyno and compare to a similar power Vortech V3 Si dyno and you will see.
You are correct that an engine that makes leak power at 8400 rpm is not going to make much torque at low rpm. However, there is no disputing that the positive displacement makes full boost much much much sooner on this motor and has a dramatically better low end power curve. That is a function of how the PD blower works in contrast to how the centrifugal works.
The benefit of the PD is also it’s disadvantage on the high compression S65. It can’t be set up provide as much boost as it could due to concerns about knock and rods that are present at the higher VE levels that exist in the low to mid range. If you installed stronger rods and ran higher octane and let it boost to 8 psi like the typical high power centrifugal kit, any advantage the centrifugal still had due to higher efficiency would show up at much higher rpm rather than the entire 2nd half of the power band.
From 2000-4000, the PD wins every time. From 4000-8000, the centrifugal wins. Any all out race the centrifugal wins because you are under 4000 only during the launch. Honestly, I find the torque of my modded NA E90M3 to be perfectly fine for lazy low rpm daily driving around town. I’d rather add top end power for the occasions when I hot rod around. The only situation where I would want more low end is highway cruising in 5th or 6th, where I wanted to be lazy and not downshift. The PD blower would be nice there. With the centrifugal I would still be downshifting. My car is 6MT; those of you with DCT can do tremendous downshifts with zero effort. My next car will be auto or DCT and turbo