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Centrifugal blower vs. turbo: Which nets more power?

Discussion in 'The Hokey Ass Message Board' started by Brad54, Feb 3, 2012.

  1. Brad54
    Joined: Apr 15, 2004
    Posts: 6,015

    Brad54
    Member
    from Atl Ga

    :D
    This is a direct rip-off of the Roots vs Round blower thread.

    I've had lots of heated discussions when a friend about which makes more power, a supercharger or a turbo charger.
    Specifically, we've discussed which has more parasitic drag.

    His feeling is they're equal, because they're both spinning something that is creating pressure, and that pressure creates resistance. (I'm simplifying it)
    He believes there is resistance on the pistons on the exhaust stroke, as they are pushing the turbo impellers, which have resistance as they compress the incoming charge.
    He thinks this resistance is about equal to that on the crank of a supercharged application, as the supercharger is compressing the incoming charge.

    I say there isn't as much loss in a turbo, because the impellers are in the exhaust stream and the cut of the impeller vanes affects the efficiency the turbo spins--and therefore compresses the incoming charge on the other side of the housing. It's a poor analogy, but I liken the vanes to a lever--one "increment" of force to turn the vanes isn't the same as the increment of force to turn the compressor vanes.

    So what's the HAMB say? Which takes less power to spin--a turbo or a round blower?

    (and for the trad police... we're planning for a Bonneville stude)

    -Brad
     
  2. 42hotrod
    Joined: Nov 3, 2005
    Posts: 811

    42hotrod
    Member
    from S.E. Idaho

    I have always heard the turbos have way less parasitic drag, you don't have a belt turning anything. I know in Drag Racing the hardest part has always been spooling them up rapidly, but with the modern ignition boxes out now that actually fire the cylinders with the exhaust valves open when the trans brake is depressed this has been solved. It sounds like rapid gunfire, only louder if you've ever seen one run!

    As far as what your buddy says, I totally 100% disagree, with the exhaust gases still expanding near when the exhaust valve opens, the engine has no clue the turbo is there, it is pushing out the still expanding gases anyway.

    Scot
     
  3. gotit
    Joined: Aug 27, 2009
    Posts: 357

    gotit
    Member

    If it doesn't know it is there then why is there drive pressure on a turbo application? I will say there are ways around higher drive pressures if you are not worried how long it takes to spool. Getting the biggest trim and aI loose housing will greatly reduce drive pressure resulting in slower spool times.
     
  4. 42hotrod
    Joined: Nov 3, 2005
    Posts: 811

    42hotrod
    Member
    from S.E. Idaho

    I Had to google it to understand it better so I get what you are saying. I should google BEFORE the post instead of after. haha

    I still feel a turbo is the better way to go and the drive pressure would be less drag than the belt driven supercharger. There has to be some direct tests, gonna have to google it more!

    Scot
     

  5. Turbo is more efficient because you are using the heat energy in the exhaust that is otherwise lost to the atmosphere. Any crank driven supercharger takes away from the power available at the crank end. A turbo does create more backpressure and some loss, it is not free energy. But overall an exhaust driven turbo it is more efficient than crank driven blower.
     
  6. I seriously doubt that the exhaust backpressure created by a properly sized turbo causes anywhere NEAR as much parasitic drag as a belt driven supercharger that moves the same amount of air.

    Having said that, I stand ready to be proven wrong by facts...
     
  7. 77powerwagon
    Joined: Oct 22, 2010
    Posts: 44

    77powerwagon
    Member

    your friend is mistaken. There are actually really well written books discussing this, I'm reading one now can't remember the name of it right now but if you'd like to know just give me a shout. Hey buy the book for him and say he has to pay for it when he realizes he's wrong.
     
  8. p51mustang
    Joined: Sep 2, 2009
    Posts: 84

    p51mustang
    Member

    Turbo > supercharger
     
  9. The short answer....
    On identical engines a turbo "can" create more power. Both have loss involved, but the turbo requires less power to turn it. Something like 4 hp to run a turbo to 40 hp to run a blower..(dont quote me)
    and i say "can" make more because there are so many other things that can affect the output...intercooler efficiency , wastegate, turbo sizing, cam selection etc...etc...
     
  10. Under the boost threshold, turbos will have little or parasitic drag on the engine. A belt driven centrifugal supercharger will. Supercharger guys will also argue that not having the hot exhaust adding to the heat of the air charge being stuffed down the engine's throat makes up for the loss of turning the whole mass.

    Plenty of very fast cars using both. Both have their pros and cons. For most turbos are much easier to package into a car without having to totally re-arrange the front half of the car. Realistically, it's all a matter of your personal taste.
     
  11. I agree with you...it does come down to personal taste and desire.
    I hear the heated intake charge line all the time...then i explain that compressing oxygen heats it up...and i have an intercooler that the air charge goes through and many superchargers do not.
     
  12. deto
    Joined: Jun 26, 2010
    Posts: 2,620

    deto
    Member

    I worked in the engineering department at Vortech, right when they aquired Lysholm and were messing with screw blowers. Depending on multiple factors, centrifugal and positive displacement blowers have their pros and cons.

    As far as a turbo vs centrifugal, turbo has way less parasitic drag. If you wanna make serious HP, it takes some serious HP to turn that belt.
     
  13. 57tony31
    Joined: Jul 20, 2008
    Posts: 632

    57tony31
    Member
    from Woods

  14. Brad54
    Joined: Apr 15, 2004
    Posts: 6,015

    Brad54
    Member
    from Atl Ga

    I'd love to buy the book... what's the title?

    -Brad
     
  15. metalshapes
    Joined: Nov 18, 2002
    Posts: 10,703

    metalshapes
    Tech Editor

    I've built a McCulloch blown SBC Hot Rod and a Turbocharged 351W Streetfreak.

    The cars are pretty different and the 'charging systems are too.
    So comparison is difficult.

    The Turbo surprised me the most.
    Its a old fashioned Draw through, so its not the latest word on Turbo technology, but I like it.
    It delivers its power different than I thought it would.
    Smoother and with more low RPM torque than I expected...

    And I'm in the last stages of fabwork for a Intercooled Blow Through Turbo.
    ( 2.3 Pinto converted to Carb )
    Again with a totally different vehicle from the other 2.
    I'm curous what I'll be able to learn from that one.
     
  16. SvenOla
    Joined: Aug 28, 2011
    Posts: 58

    SvenOla
    Member
    from Sweden

    .... what most other says , and parasitical drag creates heat too .....
     
  17. 42hotrod
    Joined: Nov 3, 2005
    Posts: 811

    42hotrod
    Member
    from S.E. Idaho


    That turbo'd 2.3 is going to blow your mind. I kinda like the lil 2.3's. I had a Merkur XR4TI (remember those?) Turbo 2.3, T5 5 speed and an independant rear suspension. I had it tuned up a bit, boost to 14 lbs, exhaust and that was about it. My buddy had a 5.0 mustang and I could run with him all day long LOL.

    Have fun!


    Scot
     
  18. squigy
    Joined: Nov 30, 2003
    Posts: 3,915

    squigy
    Member
    from SO.FLO.

  19. Brad54
    Joined: Apr 15, 2004
    Posts: 6,015

    Brad54
    Member
    from Atl Ga

    Some more input from my buddy:

    "1) a turbo and a round blower are the same thing. Only one drives the input shaft by a belt and one drives it by a second fan turned by exhaust gas.
    2) If you put 15 lbs of boost on one side, on one fan, and the other fan is connected via shaft, it takes that much force to turn the second fan. Period.
    3) both are connected to the crank.
    Most people don't think about the pressurized intake tract trying to prevent the fan from turning.

    The round blower has a belt that's driven by the crank.
    The turbo has cylinder pressure that pushes the second fan. That backpressure is pushed by the piston, then the rod, and ultimately the crank.

    They're both driven by the crank. The crank has to push the piston and exhaust gases - with 15 lbs of backpressure - out.

    And we haven't even talked about the exhaust backpressure that plugs up the system. That can't be a good thing. Reversion is when you have a lot of backpressure and you can't efficiently move ALL the spent exhaust gases out of the cylinder. So now the cylinder isn't empty when the valves close and the intake stroke starts. So it can't take a full load of clean air and fuel, you get a partial load. Which means a smaller bang.
    So the turbo has an advantage with expanding hot gases but the round blower would seem to me to have an advantage in having no exhaust backpressure, although I'm sure there's some disadvantage in belt friction too."



    So those are his points.
    I'd love to hear people's thoughts!
    -Brad
     
  20. mattcrp1
    Joined: Aug 20, 2007
    Posts: 401

    mattcrp1
    Member

    First off let me say most of me experience is with off topic EFI gas and diesel for the turbo vs. supercharger. With that said the application needs to be considered, turbos are typically high rpm power where superchargers are more of a low end thing. Engine size and fixed or variable vane turbo make a huge difference. the super charged 5.0l stang i built had a lot of low end get up and go but the turbo ranger <2.3l turbo> had a lot of power on the top end.
     

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