Supercharger vs. turbocharger: parasitic loss

Discussion in 'Technical' started by Big Rob, Jul 25, 2007.

  1. #51 bentheswift, Aug 1, 2007
    Last edited by a moderator: Apr 25, 2016
    "do some research before you go making assumptions...
    I hope you have learned something valuable today." - Archangel06

    See, engineering students are kind of required to do their research. Otherwise, they end up making stupid assumptions like "an F1 engine could not possibly move a Mack truck".

    I checked out your link and spent some time looking up the specifications of the Mack MP8 415C 13-liter turbodiesel inline six. has a spec. sheet with a dyno graph:
    1660 lb-ft from 1100-1200rpm, with 415 peak horsepower.

    So I copied it into the spreadsheet I made over spring term (you know, the first couple weeks of the term where you actually have free time). I found a tire diameter (39.9" for the OEM 295/75R22.5 tires) and gear ratios for the OEM Fuller FRO-16210B 10-speed transmission from this sheet:

    A couple of months ago I happened across a dyno graph from a BMW Formula 1 car. The specific engine is the P86 V8 engine from the 2006 year. It revs to 19500rpm and makes about 231 lb-ft of peak torque, at around 16000rpm. F1 dynos are few and far between, and I looked long and hard for this baby. I plugged this dyno graph into my spreadsheet along with the Mack engine.

    What this spreadsheet does is take a torque curve by inputting points every hundred or so RPM across the engine's operating range, (I visually take these from a dyno graph) and then plotting that curve in a new graph of wheel torque versus vehicle speed. There is one curve for each gear. This way you can see exactly what torque is available to you at any wheel speed.

    So I plotted the Mack truck's engine in its first three gears (11.06, 8.19, 6.05), and then found ratios for the F1 engine that would make the shift points for both engines to be at the same vehicle speed. (These ratios are 110, 80, and 60...)

    I uploaded the graphs but I am not sure if I did it right (never done it here before) so here are the images on another server.
  2. So I guess that settles it, huh? The itty-bitty 2.4 liter 231 lb-ft Formula 1 engine makes more wheel torque than the 13 liter 1660 lb-ft Mack turbodiesel in every gear, at every point. The difference in peak wheel torque in first gear is over 7,000 lb-ft.

    If you guys are too stupid to read numbers on a graph, let me sum it up for you. The Formula 1 engine, properly geared, will accelerate a Mack truck faster than the Mack diesel engine, no matter how fast you're going. Wheel torque is the only thing that matters. And the F1 engine makes more of it at all velocities.
  3. Oh, this is another good quote from Archangel06:

    "3. Don't act like you know what in the hell your talking about, it pisses people off. "

  4. If they also have the same efficiency they will require the same amount of power. The difference is that the turbos compressor doesn't take the power from the crankshaft like the supercharger, instead it uses the blowdown energy. Yes, using that energy can affect pumping losses and the volumetric efficiency of the engine. With a turbo the effect on pumping losses and volumetric efficiency can both be negative and positive depending on how efficient the turbo is working. With most installations the effect is negative, at least at high engine speeds since very small turbos are used, which can provide boost very early. Even when the effect is negative, the resulting powerloss from the crankshaft is still lower than with a supercharger.
  5. I have to disagree ever so slightly. The power required to move the same flow and pressure is the same assuming the same efficiency, but the supercharger will still require more power input to get the same compressor shaft power due to slightly more friction in the step-up gearbox than the turbocharger has in its single bearing section. And if the belt is installed too tight, additional load is put on the input shaft bearing resulting in another small increase in friction.

    You can't overtighten a belt if you don't have one. <A BORDER="0" HREF=""><IMG BORDER="0" SRC="pitlane/emoticons/wink.gif"></A>
  6. #56 Monkey, Aug 1, 2007
    Last edited by a moderator: Apr 25, 2016
    Nice work. That's what I was going to try to do during my lunch break yesterday. Stupid meetings anyway.

    What these guys fail to realize is that there are some of us on this forum who ARE engineers or engineering students and (unfortunately) too often, common automotive knowledge doesn't line up with physics (e.g. what most people KNOW is happening isn't really what is happening).
  7. I think you are confusing valve area with port velocity. As I understand it (it's been a while since I've read up on it since my sister lost my combustion engines text book a while back), you always want to have as large a valve as possible to have a low pressure drop across it when it's open and then the ports are sized to achieve port velocities necessary for the desired characteristics of that particular engine.

    EDIT: And for the record, I am indeed a mechanical engineer, but I do not work in the automotive industry.
  8. One little correction... maximum valve flow area is not equal to the valve head area, it is equal to the lift times the circumference of the valve. So assuming the same lift, the 3 cm valve would have 3 times the flow area as the 1 cm valve.
  9. haha, "Psi is air density".

    Fine, you can pump in 10g/min of air, I'll pump in 100g/min. We'll both run at the same pressure and see what happens.

    You can still drive in a Corvette with 6POT brakes and a stage 2 exhaust or whatever..
  10. #60 Hollywood, Aug 1, 2007
    Last edited by a moderator: Apr 25, 2016
    I'm aware that if the gear ratios are changed in the F1 engine it would out perform the Mack Trucks engine in every area. I believe Archangel was trying to say if you traded the two out as is without modification the F1 motor wouldn't be the best choice.
  11. What you talk about is the difference in efficiency. I said the power consumed will be identical given tha they have the same efficiency, to include mechanical efficiency into that efficiency would be nothing strange.

    In any case, a supercharger and turbocharger usually see small differences in efficiency. Most centrifugal superchargers tend to be designed to operate at lower speeds (there are some exceptions), and in general these have slightly lower efficiencies. But they also tend to use ball bearings, something that turbochargers normally doesn't use. These tend to increase the mechanical efficiency at low speeds somewhat.
  12. I thought centrifugal superchargers were typically used at high speeds? You see them on Hondas alot, and they still don't make any power down low. Also, the supercharger sitting in my garage (Toyota SC12 from a 1.6l 4A-GZE, it's a roots blower) does not have a step-up gear. The supercharger pulley is directly connected to the blower. I think that a gear is only really used for centrifugal compressors. Not sure about that though.

    Just remember, most superchargers absolutely do not have efficiencies comparable to turbochargers. Centrifugal compressors can, but they are sorely limited by gearing. Lysholm compressors are the only other supercharger that can match a turbo's efficiency.

  13. Since I'm used to dealing with pumps, fans, and blowers, I'm used to distinguishing between static efficiency (or pump efficiency) and overall efficiency (including mechanical efficiency of any drive train such as belts, gears, etc.). My bad, you are correct when put in terms of overall efficiency.
  14. Both you and Archangel said that the F1 or Indy Car engine would do absolutely nothing in a Mack truck. That's completely incorrect. The fallicy is still that torque equals work when it does not. Power is the rate of work and in the case of an engine or electric motor determines how much torque can be made and what speed. When you slow the output down through a gear reduction, the torque output must necessarily go up due to the law of conservation of energy. The torque output of an engine isn't the torque available at the driven wheels.
  15. Centrifugal superchargers tend to only provide extra power in the upper reaches of the engine's rpm band. This is because that like turbos, they have to spin quite fast to develop boost and since they are mechanically driven by the engine, their acceleration rate is the same as the engine's acceleration rate. With a turbocharger, the compressor can acclerate independent of engine speed and so can provide more boost earlier in the rpm band.

    Also, I have never seen a positive displacement (roots or twin-screw) blower with a step-up gear box. Probably because they simply don't have to spin anywhere near as fast as a centrifugal compressor.
  16. well, duh! do you not possibly think he already knows this? he is an engineering student.

    you obviously have some knowledge of how engines work, more than the average person who isnt really into cars, but you dont know much at all compared to some of the people on this site. i suggest you stop posting to save further embarassment
  17. I also read an article about this, but am a bit skeptical.

    also 1psi of boost from a blower usually nets more power than 1psi of boost from a turbo charger, even though it doesnt make sense how ( this should be measuered after the intercooler(if there is one) to see an equal charge, since boost is just a measurement of pressure andnot actual amount of airflow vs CFM being the measurement of airflow.

  18. lol ure car sucks
  19. "also 1psi of boost from a blower usually nets more power than 1psi of boost from a turbo charger, even though it doesnt make sense how..."

    I would like to see some proof of this. The only way that the supercharger is making more power than the turbo when the manifold is reading 1 psi is if the supercharger is more efficient and is therefore heating the charge less... very few superchargers will approach the adiabatic efficiency of a typical turbocharger, but even if it does, the lower mechanical efficiency puts the overall efficiency back below that of the turbo.

    I'll try looking for the Hot Rod Magazine article again... it was a pretty definitive test...
  20. #71 Eatonupturbos, May 20, 2015
    Last edited by a moderator: Apr 25, 2016
    There are too many variables to correctly answer that question, so yes and no are both correct depending on the combination chosen.
    Back in 1990 it would have been much easier to get more peak power with a centrifugal charger (wether crank or exhaust driven) because of the higher efficiency numbers they had over the old twin rotor rootes chargers available at that time. Lysholm twin screw compressors may have had similar efficiency numbers as the earlier turbo's, I haven't bothered to investigate them because they are overpriced and out of my budget. The new design TVS Eaton blowers now have efficiency figures equal to that of most turbochargers, so it is entirely possible to create as much or even more power with these modern blowers.
    Turbochargers don't run on free energy, they run of energy that is created by the fuel/air mix that has just been burned in the cylinder, and are actually a restriction to exhaust flow. There is another way to harness the exhaust blowdown energy without using a turbocharger to increase mass flow of fuel/air through an engine by using a well tuned set of headers, so there was never any "free energy" available to power a turbocharger to start with. Well equipped/experienced racing engineers know how to design a set of headers can harness this energy and create a suction so strong that the intake mixture is actually sucked into the cylinder during the valve overlap phase, this phenomenon is called the "5th stroke" in the 4 stroke cycle, and can have the same influence on volumetric efficiency as that produced by 7 pounds of intake boost. Here is an article that explains how it works-
    So....If you can design an efficient exhaust header/system that improves V.E., then the crank driven blower is out in front from the get go because a lower boost pressure will move the same amount of mass air than what a backpressure creating turbocharger setup will.
  21. #72 Turbocharger11, Nov 17, 2015
    Last edited by a moderator: Apr 25, 2016
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  22. #73 Turbocharger11, Nov 17, 2015
    Last edited by a moderator: Apr 25, 2016
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