Discussion in 'Superchargers, Turbos, Nitrous' started by grumpyvette, Apr 22, 2009.

  1. grumpyvette

    grumpyvette Administrator Staff Member

    here is the perfect turbo for all you cheapskates, that are clueless about how engines work and whats required to produce effective boost on a running engine


    http://www.j-body.org/forums/read.php?f ... 1&t=113561

    http://www.amazon.com/Air-Intake-Superc ... 6432768-20




    OH YEAH! a bilge evac fan is going to be a REALLY effective power adder. NOT!
    theres always scams and this is one!
    anyone dumb enough to buy and install one, expecting a big boost in hp deserves the wasted expense and result, at least the twin leaf blowers ive seen used on a different carm, have a slight chance of SLIGHTLY increasing air flow rates, the bilge fans hopeless

    look any first year physics class will quickly point out that it takes more electrical potential than any cars altenator can provide to power an electrical motor thats able to provide the necessary boost in intake manifold pressure levels that would result in a decent power gain, of more than a couple hp on a 350 cubic inch v8, naturally someone always points out that leaf blower on the honda 4 cylinder,
    well the results on an engine 5 times that size will be less than 1/5 as good at best ( making it almost basically TOTALLY useless past 2000-3000rpm, where engine consumption easily runs away from the leaf blower out put, as far as building effective additional manifold pressure goes)


    Many Electric Superchargers advertised on the internet are in fact marine bilge fans or similar blowers that do much the same job. These are designed to ventilate confined spaces which they do well though unfortunately they do not make good automotive superchargers. Bilge blowers and their like mostly lack any form of diffuser (not required by and slightly detrimental to their intended function) which means they do not generate pressure efficiently (if at all). A diffuser is a static set of vanes arranged closely around the rotating compression wheel that allows a pressure wave to build up on their leading edges. Pressure can only be developed when there is a resistance to air flow and a diffuser provides that resistance without being too much of an impediment. You can think of it as a sort of one way valve that allows air pressure to build up in a moving column of air. Without an increase in pressure a supercharger is likely to be next to useless and shouldn't be called a supercharger at all. Another reason that bilge blowers do not make good superchargers is they simply are not powerful enough. Most are rated between 50W and 200W which is far below the minimum power that our testing indicates. Other similar advertised electric superchargers employ ducted fans as used in model aircraft. Technically these are axial impellers and would require a set of stator vanes to fill the same function as a diffuser in radial compressors if they are intended to produce an increase in air pressure. Ducted fans are usually designed to produce a high velocity air stream, eg to create thrust in a model aircraft. An increase in pressure requires a reduction of velocity in a moving column of air (pressure and velocity are inversely proportional) so these types of fans do not have a stator and are not designed to produce pressure. The very best of these bilge blower and fan type 'superchargers' may be of some benefit but the majority are a waste of time and money"
  2. grumpyvette

    grumpyvette Administrator Staff Member

  3. grumpyvette

    grumpyvette Administrator Staff Member

    HEY GRUMPY, seriously, I have often wondered why electric blowers aren't more common for mild (low-psi and occasional use) street applications. There's zero parasitic hp loss, total computerized boost control capability, and simple/flexible installation options. Are electric motors just not powerful/compact/light enough? Motor and battery technology have really advanced just like everything else. Imagine the low end torque and immediate throttle response of a mode where the blower maintains full psi even at idle!

    OK being an engineer I can,t even begin to stop laughing at the concept. of an alternator running an effective electric supercharger.
    DON,T CONFUSE CUBIC FEET PER MINUTE OF AIR SPEED WITH BOOST UNDER PRESSURE, YOULL OCCASIONALLY SEE , something like a leaf blower advertized as flowing 1000cfm, but thats at near zero pressure, that 200mph leaf blower if hooked to a pressure gauge and working against BACK PRESSURE would be hard pressed to provide 2psi with zero leakage, start sucking off 600cfm by hooking it to the intake on a running engine and you quickly find near zero positive pressure,as it can,t keep up with demand, the best youll see is a reduction in the negative pressure, the engine might go from -3psi vacuum to -1 psi vacuum at 6000rpm
    lets start with the requirements, the super charger needs to compress enough air to provide actual pressure in the intake plenum WHILE the engine RUNNING.
    lets take a 350 sbc and we want to make a modest 5psi of boost at 6000rpm, , your engine normally runs with a negative pressure or vacuum in the engine, a very well designed intake at wide open throttle will allow the outside air pressure, to flow thru the intake reducing that vacuum from a 18-14 inches of vacuum at idle to maybe 3" of vacuum at wide open throttle and your engines flowing about 600cfm at that speed, you can expect about a 6.5% boost in hp for every 1 psi of boost ,applied to the N/A hp up to the point octane limitation gets you into detonation and remember compressed air is hot air, and the hotter the intake charge temperature is the less oxygen it contains per cubic foot,and the more likely youll get into detonation, thats why inter-coolers were invented.to boost the manifold plenum pressure to only 5 psi positive pressure you would need to have the supercharger provide about 1100 -1300 cubic feet of air at 5 psi while the engines running. it would not be unexpected to have a supercharger that boosted a 350hp N/A engine to potentially 460-480hp to use about 50 hp or more to do it in heat and friction and related power losses

    Calculate manifold pressure required to meet the horsepower, or flow target

    MAPreq = ( Wa x R x (460+Tm) ) ÷ ( VE x (N÷2) x Vd )

    MAPreq = Manifold Absolute Pressure (psia) required to meet the horsepower target
    Wa = Airflow actual (lb/min)
    R = Gas Constant = 639.6
    Tm = Intake Manifold Temperature (degrees F)
    VE = Volumetric Efficiency
    N = Engine speed (RPM)
    Vd = engine displacement (Cubic Inches, convert from liters to CI by multiplying by 61.02, ex. 2.0 liters x 61.02 = 122 CI)


    To continue the example above, let’s consider a 2.0 liter engine with the following description:

    Wa = 44 lb/min as previously calculated
    Tm = 130 degrees F
    VE = 92% at peak power
    N = 7200 RPM
    Vd = 2.0 liters x 61.02 = 122 CI

    MAPreq = ( 44 x 639.6 x (460+130) ) ÷ ( 0.92 x (7200÷2) x 122 ) = 41.1 psia

    (remember, this is absolute pressure. Subtract atmospheric pressure to get gauge pressure (aka boost):

    41.1 psia – 14.7 psia (at sea level) = 26.4 psig boost

    As a comparison let’s repeat the calculation for a larger displacement 5.0L (4942 cc/302 CI) engine.

    Wa = 44 lb/min as previously calculated
    Tm = 130 degrees F
    VE = 85% at peak power (it is a pushrod V-8)
    N = 6000 RPM
    Vd = 4.942 x 61.02= 302 CI

    MAPreq = ( 44 x 639.6 x (460+130) ) ÷ ( 0.85 x (6000÷2) x 302 ) = 21.6 psia (or 6.9 psig boost)

    This example illustrates in order to reach the horsepower target of 400 hp, a larger engine requires lower manifold pressure but still needs 44lb/min of airflow. This can have a very significant effect on choosing the correct compressor.

    With Mass Flow and Manifold Pressure, we are nearly ready to plot the data on the compressor map. The next step is to determine how much pressure loss exists between the compressor and the manifold. The best way to do this is to measure the pressure drop with a data acquisition system, but many times that is not practical.

    Depending upon flow rate, charge air cooler characteristics, piping size, number/quality of the bends, throttle body restriction, etc., the plumbing pressure drop can be estimated. This can be 1 psi or less for a very well designed system. On certain restrictive OEM setups, especially those that have now higher-than-stock airflow levels, the pressure drop can be 4 psi or greater.

    For our examples we will assume that there is a 2 psi loss. So to determine the Compressor Discharge Pressure (P2c), 2 psi will be added to the manifold pressure calculated above.

    P2c = MAP + Ploss

    P2c = Compressor Discharge Pressure (psia)
    MAP = Manifold Absolute Pressure (psia)
    Ploss = Pressure Loss Between the Compressor and the Manifold (psi)

    For the 2.0 L engine: P2c = 41.1 + 2 = 43.1 psia

    For the 5.0 L engine: P2c = 21.6 + 2 = 23.6 psia

    Remember our discussion on inlet depression in the Pressure Ratio discussion earlier, we said that a typical value might be 1 psi, so that is what will be used in this calculation. For this example, assume that we are at sea level, so ambient pressure is 14.7 psia.

    We will need to subtract the 1 psi pressure loss from the ambient pressure to determine the Compressor Inlet Pressure (P1).

    P1c = Pamb - Ploss

    P1c = Compressor Inlet Pressure (psia)
    Pamb = Ambient Air pressure (psia)
    Ploss = Pressure Loss due to Air Filter/Piping (psi)

    P1c = 14.7 - 1 = 13.7 psia

    With this, we can calculate Pressure Ratio (∏c) using the equation: ∏c = P2c ÷ P1c

    For the 2.0 L engine: ∏c = 43.1 ÷ 13.7 = 3.14

    For the 5.0 L engine: ∏c = 23.6 ÷ 13.7 = 1.72

    We now have enough information to plot these operating points on the compressor map...

    Information Provided By: Garrett Performance Products

    http://horsepowercalculators.net/turboc ... -explained
    http://www.ehow.com/how_5149949_calcula ... ssure.html

    a normal alternator puts out about 100-130 amps at about 13-14 volts peak,volts x amps = watts so 1820 watts its the max you have to use
    Divide the wattage by the conversion factor is 746 Watts per HP, or about 2.5hp, is the max you could generate and remember the engines already using about 80% of that to keep the car running and battery charged.youll need about 50hp or 20 times as much to have a electric powered compressor provide the required boost, powered from the alternator


    Read more: How to Convert Amps to HP | eHow http://www.ehow.com/how_5946332_convert ... z2T6Ppq4S9

  4. Grumpy

    Grumpy The Grumpy Grease Monkey mechanical engineer. Staff Member

    more proof that fools and cash are rather easily parted
    I really don,t doubt some people are really dumb enough t waste $400 plus on this junk,
    I've had several people, want to debate the merits or potential advantages of these electrically powered fans.
    too boost engine power, every test Ive ever seen .
    showed a marked reduction in the power.
    Last edited: Oct 5, 2019

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