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I found this on the Steeda site. I'm more in the PD camp myself but thought I'd post and let the debate spool up.
At Steeda Autosports, our DNA mandates that we are constantly testing and pushing the levels of vehicle performance above and beyond the norm – all in the quest of ensuring that our customers have the option of purchasing the best performance products available anywhere. When it comes to superchargers, we have done a tremendous amount of testing on the dyno, on the street, at the drag strip and at the race track – and we can unequivocally state that there is only one type of supercharger that we have found that offers the sustained power and efficiency in an integrated package.
There are essentially two types of superchargers in the market today, a Roots type and a Centrifugal type – and there are major reasons why you should only consider one over all others. These reasons all are based on our real world performance evaluations, not marketing hype or driven by profits – rather these are our own observations after thousands upon thousands of miles of rigorous testing.
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Let us explain…
Roots Type Superchargers
Many auto manufacturers opt for the Roots type supercharger for a variety of reasons, the most prevalent reason being lower Tier 1 cost. It should be noted that this type of supercharger is not actually a compressor – rather it is just an air mover. Specifically, air moves on the housing sides within the rotors voids. By virtue of moving air into the cylinder heads at a higher rate than the engine consumes it, pressure is built. But sustained efficiency and power are lacking for a variety of reasons, namely:
Heat Soak Effect – This is a major issue with the Roots design that is sold today and it simply cannot be avoided with this type of design. Whenever you operate a Roots type supercharger, it is probable that almost half of the input power is consumed to make heat rather than power – essentially creating a parasitic power drain on the engine. We have equipped our own race cars with the best Roots system money can buy, only to discover that after just a few laps the engine becomes heat soaked and power levels dramatically decrease. Even with extensive intercoolers, you simply cannot overcome this devastating issue – we have tried to no avail. Advocates of the Roots systems will usually showcase dyno runs on cool engines, preferring not to show a real world effect that driving on the street or racing would have as the engine warms up and loses its performance gains.
Weight – We all know that weight is the enemy of performance, a typical Roots supercharger easily outweighs a Centrifugal type and in addition, it requires a more substantial cooling system – adding yet even more weight to the supercharger package – and this weight is at the worst possible location, by being principally on top of the engine raising your vehicle’s center of gravity.
Efficiency – Adiabatic efficiency (the real measure of a supercharger’s efficiency) is where the Roots type fails miserably with efficiency ratios typically in the low 50% or below range. This causes excessive heat build-up and parasitic drag on your engine. Centrifugal type superchargers operate typically in the mid to upper 70% range. The major cause of this inefficiency is based on the inherent design of the Roots system where you have reversion occurring as the rotors open up and pressure is normalized in the manifold.
Boost curve – Advocates of Roots systems point out that they make their power at low RPMs. While this is true, this feature is actually much less helpful than it appears. Realizing that excessive boost cannot be utilized at these low speeds due to traction limitations and also on most engines the ignition timing must be significantly retarded to avoid destructive detonation. Additionally, low engine speed is not where power is made… rather it is the higher RPM band where you want your boost and subsequent power and this is where the centrifugal supercharger really shines.
Removal of Tuned Intake Runners – Installation of a Roots type supercharger requires removal of the tuned intake runners – resulting in a loss of those free benefits – whereas a Centrifugal Supercharger leverages the tuned intake runner benefit to the max.
Centrifugal Superchargers
Serious performance aficionados and racers know the real benefits that centrifugal superchargers provide. When you want serious supercharger power, power that is available before your engine gets heat soaked, and power that is available when you need it – then the only alternative is a centrifugal supercharger. As part of our real world testing, we have tried all of the most popular superchargers under essentially all conditions. At the extreme level, when we equipped our #20 race car with a Vortech supercharger and ran some of the most grueling laps possible at Sebring, Daytona, and Palm Beach Raceway, we obtained absolutely superb results… far better and much more consistent results than when we had a Roots type installed on it. On our street cars we have put untold thousands of miles testing under virtually all conditions – hot, cold, wet, dry, stop light to stop light, and on the drag strip and autocross track… all with the same truly exceptional results. Vortech supercharger systems are a great value. Dollar for dollar, Vortech systems deliver more horsepower than virtually any other method of upgrade. Also, driven normally, gas mileage often increases rather than decreases.
With power that does not fade, superior efficiency, and full 50 state emission compliance, the Vortech Centrifugal Supercharger earns the Steeda Seal of Approval as being our preferred supercharger of choice.
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Originally Posted by Stephen06GT
