Many people on this and other forums seem to endlessly debate which type of "power adder" system - forced induction or turbo - is "best".
Some time ago, Muscle Mustangs & Fast Fords (MMFF) did two-part article detailing a side by side comparison of four separate systems - (1) roots; (2) twinscrew; (3) centrifugal; and (4) turbo - installed on a 4-valve Cobra to determine the performance characteristics of each in terms of their respective power and torque curves.
For those who don't want to take the time to read these articles in toto, here are the conclusions as summarized by MMFF:
Check out the supplied power and boost graphs for a complete rundown on how each system performed. As expected, the Eaton blower provided immediate boost response and despite the short-runner factory intake, produced impressive low-speed and mid-range torque numbers before falling off at higher engine speeds. The torque output of the supercharged four-valve motor exceeded 500 lb-ft from 3,100 rpm to 5,200 rpm. Spinning slower to keep the maximum boost pressure in check, the twin-screw lost out slightly at the lower engine speeds, but made up for the difference in blower speed with improved efficiency. Where the boost pressure fell off with the Eaton supercharger, the boost (and power) kept climbing with the Kenne Bell blower.
As expected, the Vortech out-powered the other superchargers at the top of the rev range, but lost out in terms of torque production big time compared to the positive-displacement blowers. Like the centrifugal supercharger, the turbos lost out at the lower engine speeds until the turbos came up on boost. Below 3,600 rpm, the Roots blower was the clear winner, but once the tach needle swung past 3,600 rpm, it was all turbo. How does an extra 178 hp and 154 lb-ft of torque sound? While the turbos were down by as much at 100 lb-ft at 2,500 rpm, they quickly made up for lost time by eclipsing the Eaton and producing the most impressive (post-4,000 rpm) power curves of the bunch. Check out the power and boost graphs and check back with us next issue when we crank up the test pressure on each system to 14 psi and bring you a test on the effect of runner length.
If you are interested in the theory behind the various forms, check out last month's issue. Basically, the positive displacement superchargers offer immediate boost response with the twin-screw bettering the Roots blower in terms of efficiency and power potential. The centrifugal supercharger offers even more power per pound of boost than the positive displacement superchargers, but lacks the response rate of either. In life, there is always a trade off and the turbo is no exception. Despite besting all the forms of supercharging in terms of peak power and torque, the turbo lagged behind the Roots and twin-screw blowers at the lower engine speeds.
Saw this article very good read.I'm a turbo fan, someday may have one on the stang. Thats a big difference in power even though it doesn't come on till above 3k. When it does come on you know it immeditaly. Some of that could be from the turbo size to.
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2007 Vista Blue GT, JLT cold air and SCT 3 tuner,tru-fiber ramair hood, upr adjustable upper, tubular lowers,Pypes muffler delete, wms stealth hood-pins, roush rear-window louvers
FYI: performance comparisons of F/I-turbo systems 
