can someone explain how twin screws make more power

quatrini

Registered User
okay so ive just been wondering, how is it an m90 making 17 psi makes way less power then say a whipple on the same engine with the same boost level?
im thinking its either the air coming out of the twin screw sc is much cooler, or the parasitic draw from the twin screw sc is much less or both.
but just for the curiosity of it whats the real answer?
anyone know?
 
The design of the screw provides a more steady output of charge and in most cases compression is also done. Where as the M90 just moves air.
 
the m90 compresses air on the outside of the rotors where it meets the case and it is much more turbulent coming out of the blower exit. the twin screw creates boost where the rotors mesh together and creates a lot more boost pressure at the same given rpm. so in effect you create more boost at lower rpm and rob less hp from the crank, or so ive been told:D
 
I cant say for certain but its likely a combination of several factors but I imagine primarily it is to do with the air flow of the superchargers. I know when dealing with compressors there is more than just PSI there is also CFM, ultimately for an engine its all about how much air goes in and out of it not necessarily about what pressure that air is at, the PSI is merely a restriction causing the compression. You see this more in regards to turbo charging, possibly because there is a much greater variance in turbocharger compressors than there are positive displacement type superchargers but its not uncommon for someone to upgrade a turbo and gain more power without particularly effecting boost pressures. It is also likely that newer designs also produce less heat or are less prone to heat soak but I'd be surprised if this was a significant factor because of intercoolers still being needed.
 
okay so ive just been wondering, how is it an m90 making 17 psi makes way less power then say a whipple on the same engine with the same boost level?
im thinking its either the air coming out of the twin screw sc is much cooler, or the parasitic draw from the twin screw sc is much less or both.
but just for the curiosity of it whats the real answer?
anyone know?

You are making false assumptions here. A twin screw does not make a lot more power at the same boost level as compared to a roots. There are many factors that combine to produce any given result.
 
i suppose dave is right, i am assuming. but the assumption i made comes from dyno numbers where an m90 makes 300 hp 400 tq and a twin screw makes 420 hp and 400 tq. these are made up numbers, and i understand hp isnt a force but instead a value determined by a mathematical formula, i just was uncertain on the pros and cons of each i guess.
but thanks to the replies i now have a little more knowledge on the topic. so thanks everyone for the replies!
someone on the mustand forums told me tvs rotors swap right into the m90 case but i find that hard to believe. the inlets and outlets would need to be modified significantly but i do think itd be cool to have a tvs based m90
 
i suppose dave is right, i am assuming. but the assumption i made comes from dyno numbers where an m90 makes 300 hp 400 tq and a twin screw makes 420 hp and 400 tq. these are made up numbers, and i understand hp isnt a force but instead a value determined by a mathematical formula, i just was uncertain on the pros and cons of each i guess.
but thanks to the replies i now have a little more knowledge on the topic. so thanks everyone for the replies!
someone on the mustand forums told me tvs rotors swap right into the m90 case but i find that hard to believe. the inlets and outlets would need to be modified significantly but i do think itd be cool to have a tvs based m90

Phil's car made 400/415 with an M90. Don't believe all the hype you hear. The newer design blowers are more efficient at higher airflow levels due mainly to their larger displacement. TVS rotors do not fit in nor would they work well in an M90 case. There is a lot more to the new gen blowers than just the rotor pack. The biggest problem with the M90 is it's small displacement, high rotor rpms, and resulting spotty reliability. It's amazing how much better things work when they are being operated within their original design parameters.
 
Like we've seen, the TVS and the AR make similar power. A lot of that has to do with the open inlet design of the new generation blowers. The M90 has a restrictive inlet (not just the plenum, the inlet design of the blower), which takes more HP to turn to create the same amount of boost compared to the 1.7 AR. Ever wonder why the AR makes more power, on average, than the M90 does even though it isn't much bigger than an M90?
 
has anyone done an m112 swap? and is there a possibility to run an intercooler on it?

I did it. Was not happy with the total HP numbers (but then Im never happy with what my car makes). Yes it needs intercooling as it generates a lot of heat. Best TQ number was 450 rwtq so it was fun to drive on the street, just couldn't perform in the higher RPMs and make HP. Went to a whipple and made 121 hp more. So not a fan of the M112

Ken
 
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