Well here is not exactly what I'm looking for, but in the Outlaw 10.5" slick racing they say you can use a roots blower, but not a screw type compressor (i didn't put that part in caps, they did )

Single or dual turbocharger allowed (See weight Adds)
MAX TURBO SIZES: 101mm maximum single on Big Blocks. 105.000 max single on Small Blocks (see weight section) 80.000mm max ea for twins on small blocks only. Turbo is measured on the inlet compressor wheel diameter (tip-to-tip) at the point where the leading edge of the compressor wheel meets the inlet housing and also inside diameter of the inlet.
Centrifugal blowers are limited to single only. Intercoolers are allowed. Roots-type limited to single supercharger. Roots-type size limited to 14-71; 19 inches maximum case length, 11 1/4-inch case width, rotor cavity diameter 5.840 inches maximum, variable multi-speed supercharger devices prohibited. NO SCREW-TYPE SUPERCHARGERS. Supercharger restraint systems required on Roots-type units.

Cited: http://www.pscaracing.com/Rules/rule...lawstreet.html

It still doesn't say "due to the rigorous amounts of off idle boost provided by the wonderful twin screw type compressor, we regret to inform racers that they will have to resort to using a lowly roots blower" I'll find a better source for you moregrip.

 

I found this on the NHRA website under TopFuel Rule Revisions

Page 194 (1/04)
Supercharger: Remove all reference to Whipple supercharger in section

not sure what it means though

 

Keep in mind the turbo on the STS system will run cooler than a typical front mount turbo. That alone will increase the lifespan.

 

are they as dependable as a roots?

 

very weak at best They might be a saftey hazard for all I know

BTW, I'm looking for your rule now too, but I'm not flip-flopping, I promise!

 

safety hazard...pffft whatever Hey dude, I'll PM you with new info. I think we highjacked this thread too much LOL. Trust me I'm not hiding either.

Um...STS. Do you turbo guys let your turbos cool down before you shut off the engine? I have heard of doing this so that oil doesn't boil on the bearings.

 

hey no problem.
For those that don't want to read all the previous info my position is:

Here is a link to some real info about a twin screw compressor.
http://www.lysholm.se/PDF/diagram_lys2300ax.pdf
In this case, it references the Lysholm 2300ax. Maybe if Magnuson would come out with a detailed readout of their M-112 blower we could at least compare some real data
OK, lets anylize this a bit. We always hear about the Radix/Roots supercharger's main weak point right? "Heat". Specifically, heat at higher boost levels. Now, what about the Twin Screws main weak point? "Off Boost Conditions". Specifically, The Twin Screw is still compressing air internally even during non-boost conditions and this generates heat and has more parasitic drag on the engine during non-boost even with a bypass valve. Now, thinking about this logically, do you really think when sitting at idle (i.e. off boost) that the Twin Screw supercharger is able to overcome its biggest disadvantage fast enough to build boost quicker than a modified roots/radix supercharger in its most ideal condition? Meaning, off idle, a modified roots, only has productive boost to build, while a Twin Screw, has to overcome its biggest drawback before producing productive boost (even though once it starts to build boost, it is more efficient).
Hence, the reason Mercedes Benz does use some Twin Screw (Lysholm) superchargers on their super cars and they employ a clutch to disengage the supercharger from the crank shaft during non-boost conditions to counter the negatives of the Lysholm superchargers.
Lastly, on daily driven vehicles, how often are we at an "Off Boost Condition"? I say, half of the time, like when we come to a stop light, idle, or have to slow down for traffic. Advantage, Radix!
Food for thought...why have roots blowers become "modified" by twisting the impeller lobes?
This is why the rotors are twisted:
Eaton rotors are twisted 60 degrees. Helical rotors, along with specially designed inlet and outlet port geometry in the blower case, help to reduce pressure variations resulting in a smooth discharge of air and a lower level of noise during operation. This arrangement, also, improves efficiency. With helical rotors, the supercharger can run at up to 14,000 rpm, making for a small blower for a given boost and air flow output.
They leak air
A roots based supercharger does not "leak air". It is a different design, that's all. It pushes air, not much else to say about that really. However, In essence, what Eaton has achieved, is to bring the adiabatic efficiency up from a low 50% to over 60%.
Where a roots supercharger suffers from reverse flow, or pulse, the Eaton has a 60° twist designed into the rotors to effectively reduce this problem. By introducing the opening lobe cavity at an angle, as well as the introduction of an extra lobe to increase the frequency of this event, less reverse flow is experienced.
Really? This is what came off of one of your sources. "The primary reason that blowers aren't optimized by their manufacturers is that the tooling necessary would push the cost into an area which would make the units prohibitive to the OE marketplace, which is "the" big consumer". I know this was taken a bit out of context as they were mainly describing why the housings and such of blowers are not hand finished. But the tooling needed to make a twin screw lobe is several more times the cost of a roots lobe.
BTW: If that were the case, then why is Eaton getting liscense to sell twin screw compressors instead of roots blowers? Why does the new Pherd GT use a twin screw compressor?
As for production vehicles, my thoughts are: there is no more reliable way to supercharge a vehicle than with a roots type blower, this is fact.
So reliability is my #1 reason
Cost is #2. Note: however, if the Twin Screw was mass produced at the level the Roots type are they would be cost effective as well.
With its low production cost and its improved efficiencies, the Eaton dominates the world's production, accounting for over 90% of the superchargers produced.
Lastly, I am not saying a Radix is more efficient, I am saying it produces the quickest off idle boost..........which.......IMO........for street vehicles is the most rewarding

 

One of the benefits of the STS system is that mounted in the rear, the turbo runs 500 degrees cooler. There is no need for a turbo timer. Also, there is always a fresh oil supply to the turbo.
I could only speculate on the reliability compared to a roots and my opinion is it should be at least as reliable, or better. The only experience I have to go on is with the SC's on GTP's from working for G.M. for 5 years. It is not uncommon for a GTP to come in with the SC making noise even at less than 50k. I also realize that we are talking aftermarket to O.E.M.
I do love the performance of my STS. It gives what I think is the best of both; bone stock driveability and 400plus hp.

 

Ah geez
Actually the hotter air *would* build (pressure) faster. But that is not the point to power increase the mass of the air is.
Oh you stumbled

 

hey, you cheated, I thought you said PM?

Now how can I logically trust a cheater blowing hotter air?
even if you are more efficient about it