Supercharger/Turbo Selection Hints for n00bs.
I'll do this as a series of posts so it's easier to digest. I don't like blower cars so you can bet your butt I don't have a dog in this race. Info here is based on facts and observations. The little opinion I'll give is just my opinion. You'll want to notice it and sort it out as needed.
This is going to be basics. No making complex decisions without knowing what you're selecting. We'll dive into more detail as time allows.
Boost types. We'll focus on Centri(fugal), roots, twin screw and turbo. Each will be described and the good, bad and ugly disclosed.
Boost delivery: Pick a place. Meaning pick how you want the boost to come on. Turbo's can be (but don't have to be) kinda sudden about delivering boost in the middle of the RPM band and holding steady on it to redline which can be problematic if put in the wrong car. Centrifugals develop boost very smoothly as RPM increases, roots give it all to you right away but lose the muscle up top as efficiency drops and twin screws are like roots blowers with more top end and better overall efficiency. For most people a roots or twin screw makes the most "performance" sense. Power is delivered right off the bat, holds strong and it's mega low maintenance. Twin screw is an evolved form of roots and delivers the highest output of any positive displacement (looks like a roots) blower. Higher HP numbers but lower average power come from centrifugals. Centris also spool up more like a turbo but build to peak boost steadily as RPM increases. They're a joy to tune but I hate them on the street. Most people buy them because they're inexpensive and compact. Turbos are wildly expensive to install but turn out great power when properly designed. Most systems you see on the street have too big a compressor and mighty turbo-lag. Correctly selecting your turbo will fix most of that. Turbos are HOT items. They increase underhood heat and require intercoolers for the intake charge. For most people the roots or twin screw is #1, then a centri then a turbo....simply for cost concerns.
Efficiency: This is basically the percentage of air that a blower actually moves compared to what it's trying to move. It's important to stay inside the efficient range of your compressor. Going outside that range promises to drop your average power like a used rubber and could lead to excess heat buildup and subsequent engine damage. Ever seen a massive turbo on a civic... car can make 900hp yet can't get out of its own way. Because the compressor is too big. So yeah, it can make all sorts of boost but only up really high in the RPM's and it's less fast than it was before at any RPM that's useful. Same goes with blower size... mostly.
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