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Thread: Blower Thermodynamics

  1. #1
    78Eliminator
    Question: I am reading a book that Blown472 sent me on blowers. I was reading last night that the purpose of a blower is to create a denser charge (obvious). When you compress air, it heats up, thus working against the purpose, which is to condense the charge. An example they used is that if you had a box, which was totally sealed and you stuck a pressure gauge in the side of the box and then put the box over a flame, it would heat up. As the air expands, it will create pressure (boost), which would show up on the gauge. ItÂ’s misleading since most people think that the more boost you make, the better. One way people solve this is by adding an intercooler like the "superchiller".
    My question is: do any of you blower guys have blower specs that include the ratio of compression to heat. Theoretically, if you get a blower that will compress the charge and not heat up the air as much as the next blower, you are ahead of the game. Anyone know this info?

  2. #2
    Infomaniac
    Whipples and screw blowers are very effecient. Centrifugal blowers - turbos etc are more effecient than roots blowers.
    A roots blower does not compress the air inside the blower. It provides the engine more air than it can use so the pressure is increased inside the intake manifold.
    A dyno will tell you at what point a roots blower is defeating it's purpose. You plot the boost curve along with the power curve.
    At the point the boost is increasing and the power is decreasing shows you where the air is expanding due to heat.

  3. #3
    78Eliminator
    Infomaniac:
    Whipples and screw blowers are very effecient. Centrifugal blowers - turbos etc are more effecient than roots blowers.
    A roots blower does not compress the air inside the blower. It provides the engine more air than it can use so the pressure is increased inside the intake manifold.
    A dyno will tell you at what point a roots blower is defeating it's purpose. You plot the boost curve along with the power curve.
    At the point the boost is increasing and the power is decreasing shows you where the air is expanding due to heat. So really, the best method is to take the engine to a dyno with a set of pulleys and determine which combination is the best for your application (engine set up)?

  4. #4
    Liberator TJ1984
    I read in a Street Rodder Mag. where they tested different power adders,Blower,Turbos ,NOS, but I will stick only to the Blower section they stated that a roots style blower is good for 12-15 psi before it actully starts to Rob power from its application.what you know on this INFO..???? smile_sp

  5. #5
    Infomaniac
    Justin - Honestly I do not think you would reach that point on a pump gas deal. Unless you are running a very small blower without intercooler.
    you would not be able to work an intercooled 8-71 or 10-71 on pump gas hard enough to reach that point.
    Buy a Whipple if you just want the most effecient blower.
    [ January 15, 2003, 10:43 AM: Message edited by: Infomaniac ]

  6. #6
    78Eliminator
    Infomaniac:
    Justin - Honestly I do not think you would reach that point on a pump gas deal. Unless you are running a very small blower without intercooler.
    you would not be able to work an intercooled 8-71 or 10-71 on pump gas hard enough to reach that point.
    Buy a Whipple if you just want the most effecient blower. Ok Info. The book I'm reading is just kinda scaring me. With all the heat they're talking about, you can really rattle your bottom end. With an intercooler and the biggest radiator at your disposal, I suppose this wont be much of an issue. Thanks for your input as I try to get up to par in the "Blower World"....
    J

  7. #7
    Infomaniac
    Don't just take my word for it. Wait for all the other replies.

  8. #8
    78Eliminator
    Infomaniac:
    Don't just take my word for it. Wait for all the other replies. But you're the "Infomaniac"!

  9. #9
    Blown 472
    And I thought Bill Nye the sceince guy was off the air??

  10. #10
    bigq
    Infomaniac:
    Whipples and screw blowers are very effecient. Centrifugal blowers - turbos etc are more effecient than roots blowers.
    A roots blower does not compress the air inside the blower. It provides the engine more air than it can use so the pressure is increased inside the intake manifold.
    A dyno will tell you at what point a roots blower is defeating it's purpose. You plot the boost curve along with the power curve.
    At the point the boost is increasing and the power is decreasing shows you where the air is expanding due to heat. Sounds good.I will add I believe that at the point where boost is increasing and no power is gain is where the point the engine is maxed out for the air coming in, which causes the heat. If you added bigger port heads maybe changed the cam design you would gain more power and the boost could actually read lower, but more power.
    Or you could just give it a shot of NOS and compress with a cooler charge. J/K dont try that at home kids.

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