Guys,
I have seem many examples of 'over thinking' over the course of my career, but some of the things being posted here really have raised the bar. I like how many on these forms like to say "prove it (to me?)", versus doing a little research on your own. Come on guys !
For one, there is a huge difference between the driven resistance of a turbo versus a positive displacement supercharger and it's not that hard to comfirm.
Here's a couple things to ponder right off the bat:
1 Reach into any turbo (with your two fingers) and spin the impeller. Now tell me, how much horse power did you just expend to spin that turbo impeller ? And guess what - you just expended more HP? to spin it versus when it's operational because there is NO OIL in the thing to aid it's rotation.
2 Now reach up and grab the snout on any teflon lined supercharger and try to spin it over - with 2 fingers... It will come as no surprise that many of them will take two hands and significant effort to spin it - and you CANNOT spin it fast (freely) - due to internal drag of the stripped rotors.
3 For the rest of you, reflect back on one Austin Coil (that's right, John Forces Crew Chief), who years ago developed a device called a "blower dyno". It was developed because Coil was smart enought to realize that superchargers varied in parasitic drag (mfg and assy), which pulled the HP potential of their engines down - due to internal drag and kenetic energy in the rotors which could vary by weight and pitch.
In fact, HOTROD magazine did an article years ago where Forces team started out using a hotrod 351 Ford Cleveland engine to turn the blowers over just to measure their parasitic losses. They were able to do QC on all new blowers once they started this program and it forced the serious blower manufacturers to include their findings befores shipping to future racers. We know today, the HP required to drive a supercharger because of a device called a "blower dyno". If you didn't know that, it doesn't take long to read up or query the internet. The answers are out there.
To further support my contention here, how many of you understand the concept of kenetic energy ? Well, here's a simplified version:
Take the total mass of a turbo impeller that weighs, what, 2-3 lbs, mount in on a center shaft, and spin it with your fingers. There is almost zero mass to spin, which makes it very easy to spin very fast - with just your finger. Near zero kenetic energy due to very low weight and mass.
Now mount a pair of helix type rotos on a common shaft (the drive snout), add the teflon strips (required to keep it sealed during operation) and try to spin it over with any great effect. Guess what it still takes two hands and a lot of grunt just to move it - and you're never going to see one spin with just two fingers. Very high kenetic energy due to high weight, mass, and internal resistance (teflon strips).
OK, now add the resistance from the roots rotors as the air is squeezed down (compressed) to exit the intake port, and you've got a recipe for massive drag. Albeit, they do make much more than they lose in parasitic losses, but it takes big HP to drive a blower - especially competition blowers.
On NHRA not allowing turbos in pro-stock, just take a look at the class and you quickly see they've never let it happen, nor will they let it happen. I watched Buddy Ingersol and others compete at Rockingham and monitored their efforts to get turbo cars accepted and have personal knowledge of the decisions the exclude them. That was even after the turbo crowd agreed to reduce their engine sizes to 1/2 that of the NA cars, and they were never given a chance. Get over it guys, turbo technology is king - even though most of us still love the positive displacement stuff.
In summary guys, I'm a roots-type supercharger guy myself, but there is no doubt that turbos have much more potential than superchargers ever did. If it weren't so, don't you think the diesel manufacturers would have kept on making their 6, 8-71's to this day ? It's the main reason you're forced to by the "new cases" with new kits, because most of the 'refurbs' have dried up - and nobody makes them for diesels anymore.
The mechanically driven centrifugal supercharger was an attempt to bridge both technologies; high boost levels with a reduction in heat, complimented by a reduction in rotor mass using a larger turbo wheel driven by a belt. It really all comes down to preference, but, again, turbos are king of the "lowest driven requirement per HP output".
OK, now there's my feedback on this topic. Bring on the comments, but please stop aruguing just to argue, and come back and teach the rest of us something once in a while... We'll all be better off for it.
Southernman
