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Thread: Blower Thermodynamics

  1. #11
    Blown 472
    Or run it fat, so the fuel helps cool?

  2. #12
    bigq
    Blown 472:
    Or run it fat, so the fuel helps cool? That could help too. Have a nice running idle circuit and primary with fatty secondaries for the higher end. It is hard to get it too fat on the top end, at least the application I had, a lot of air.I don't know how much more fuel would cool it, but I know it does have a cooling affect on the air charge.

  3. #13
    Schiada76
    First off I have NO IDEA WHAT I"M TALKING ABOUT!
    Other than that it sounds like you want to know what's going to give you the least heat gain in a roots blower. Bigger blower heats the air less, plus inna boat you have a GIANT radiator to keep things cool.
    Happy to be of no service!

  4. #14
    Schiada76
    BradP:
    First off I have NO IDEA WHAT I"M TALKING ABOUT!
    Other than that it sounds like you want to know what's going to give you the least heat gain in a roots blower. Bigger blower heats the air less, plus inna boat you have a GIANT radiator to keep things cool.
    Happy to be of no service! Didn't I see somewhere you were looking for 700 to 750 horsepower? I got 756 on the dyno (first pull) on my 496 w/871 no intercooler

  5. #15
    058
    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. It’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? The answer is 7 degF for each pound of boost with no outside influence such as heat created by the blower or the engine. If your blower makes 15lbs of boost the discharge temp will be raised 105 degF above ambient temp. Roots blowers are the least efficient of supercharging. They only have about a 45% rating whereas turbos are 65-70% efficient. I don't know the rating of the Whipple but its got to be close to that of the centrifical.

  6. #16
    Hotcrusader76
    Effeciency = Actual divided by theorectical mult.by hundred
    Ok...nuff said, back to studying.
    [ January 15, 2003, 03:50 PM: Message edited by: Hotcrusader76 ]

  7. #17
    Whipple Charged
    Q58, at 15lbs of boost with a roots, running gasoline through the supercharger, depending on brand, age, rotor design, would be much closer to 300-350 above ambient temp. A screw compressor would be somewhere near 120-140 above ambient as well as a centrifugal.
    To all:
    The purpose for supercharging is to raise the density of the air charge, this increases the air mass trapped and then compressed in each cylinder firing. In simple terms, the more air and fuel you can shove into the cylinder, the efficient the engine is (more power).
    Blower thermodynamics are much more complexed. First, on roots, the temp rises dramatically as boost increases. Every supercharger has an "efficiency" curve that can be plotted out like a map. This is based off of three varibles, compressor rpm, airflow and manifold psi. There are a few ways to figure efficiency, adiabatic efficency and volumetric are the most common. Volumetric measures how much air per rev. If your supercharger was 2.3L and it had a VE ration of 100%, then you would get 2.3L of air per rev. AE is the measure of the input power to which is wasted in raising the charge temp. Think about this, the blower has a discharge area on the bottom, when the manifold pressure gets positive, where is the air naturally trying to go? Simple, right back through the supercharger. This causes air to be recirculated time and time again which continues to heat up. The longer you hold the engine in positive psi, a roots will never stabilize temp and will continue to grow. Racers use nylatrol strips to actually seal the superchargers up to decrease leakage, but that causes a tremendous amount of power to operate since the surfaces are touching and so on.
    So, to answer your question (78Eliminator), its depends on supercharger make, and model (such as rotor design, discharge size and design, compressor size) as well as inlet air flow, etc. Roots doesn't really have a rule of thumb, 7 degrees per lb, thats what you would see on a 15 second sweep test on a dyno, not the real world in a boat or towing in a car. The curve is not linear.
    It's very hard to speak in general terms of superchargers for these reasons. Weiand is different than B&M, Kuhl is different than Littlefield, etc.
    Thanks,
    Dustin

  8. #18
    Nstigator74
    I'm not trying to confuse anyone, but does running methanol keep you charge temps cooler?

  9. #19
    Badboat1
    Whipple Charged, Very well said. Whipple is the strongest I have seen on the dyno and can run some boost and it will stay together.
    Badboat1

  10. #20
    Fiat48
    Nstigator74:
    I'm not trying to confuse anyone, but does running methanol keep you charge temps cooler? Yup. And 15% more horsepower by pouring it in the tank and up to 30% more horsepower if the engine is "optmized" for alcohol. wink
    K.I.S.S. method:
    An engine is an air pump
    A blower is an air pump
    There's 14.7 PSI atmospheric pressure available at 0 elevation (sea level) and 60 degree's temperature.
    Basically every time you put in 14.7 lbs of boost you double the horespower compared to sea level. (less the power required to drive the blower).
    Bump the blower overdrive till you feel no real gain in performance. Blowers vary a bunch.
    Running the engine fat is not the way to cool: creates extreme exhaust temperature and dilutes your engine oil. My 2 cents (overpriced).
    [ January 15, 2003, 09:03 PM: Message edited by: Fiat48 ]

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