Supercharger vs. turbocharger: parasitic loss

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

  1. Say you have two identical engines, but one is supercharged and one is turbocharged, and both are set to produce 5 psi of boost pressure. Will the power output of the turbocharged engine be more than that of the supercharged engine?
  2. For the short answer, most likely yes
    As for parasitic loss, the turbo feeds off the exhaust whilst the the supercharger feeds of the engine itself
  3. #4 Monkey, Jul 25, 2007
    Last edited by a moderator: Apr 25, 2016
    Hot Rod Magazine actually did a comparison test of a roots-type blower, a centrifugal blower, and a turbocharger all set to produce the same boost (9 psi IIRC). The turbo made more mid and upper-end power and in fact, the only place where the roots-type blower made more power was at the very low end of the spectrum.

    Here is one article. I'll see if I can find the other where they actually ran the same engine on a roots, centrifugal, and turbo:
  4. #5 TrueSportsCarMechanic, Jul 25, 2007
    Last edited by a moderator: Apr 25, 2016
    thank you very much for that. the only rule of thumb I remember from school on turbo/super chargeing is that for every 100 hp you make you lose 10hp with the turbo and 30 with the blower.
  5. Is the answer "yes, necessarily"?

    PSI is PSI, and the ECU should dump the same amount of fuel for combustion in both cases. We know that a bit of the resulting power is going to be lost to drive the supercharger, but what about something like exhaust backpressure for the turbocharged setup?
  6. #7 The Boss, Jul 26, 2007
    Last edited by a moderator: Apr 25, 2016
  7. The turbine of the turbocharger is actually extracting energy from the spent combustion gases. The gases enter the turbine at a high temperature and pressure and exit at a lower temperature and pressure, and all of that energy is converted into power to turn the compressor. The power required to spin the turbine is nowhere near the power required to spin a supercharger.

    But this is a very vague question. If you just want to know which one is more efficient, then it's the turbo by far. But engines do not run in steady-state operation, and everything is more complicated than it seems.
  8. O rly?
  9. Chosing between an SC or TC is about where you want your power.

    Or just get both, lol.
  10. Actually a turbocharger and a centrifugal supercharger will require the same amount of power, if they are producing the same flow/pressure.

  11. With a turbo charger you can actually producing more low end power and more high end power than a supercharger. A supercharger will end up producing linear boost to engine speed, while a turbo charger could work better across the entire engine range. What you are point out mostly is turbo lag, but that is becoming almost a non-issue.
  12. It's not though. I made 20psi on my old turbo and put down 200whp. On this one I put down 300+. The size of the turbo matters. You're moving different amounts of air based on the size of the turbo or supercharger.

    But from my experience with VWs, turbo > sc. If a SC car makes 300whp, it makes it at the very top of it's power band. The tq courve is flat and the hp curve is linear. When a turbo car makes 300whp, it makes it a few RPMs after it hits full boost, leaving 2,000 to 3,000 rpm of 300whp. In my car, when I shift I'm right back in full power. When my friend shifts in his supercharged VR6, he's down 30whp.

    Hence, I no like superchargers. They do sound great though.
  13. Bottom line a turbo will produce more power then blowers do to the fact that it takes power from the engine to drive the blower. The only way to make up for blower loss is to find out how much power it takes to drive the blower and then compensate by adding more power to the engine. A blower is more reliable then turbo. A turbo also makes sea level air density at higher elevations, while the blower doesnt. Its 7hp for every one pound of boost, either way turbocharger or supercharger, pulling high boost on a stock supercharged of turbocharged engine depends on the strength of the engine and if its been built to handle high boost loads.
  14. 1.4 liter twin charged vw engine represent!
  15. The latter half of your post makes sense, but I still don't follow how psi is not psi, regardless of the turbo. At what point the turbo really begins to get moving or how much boost it can provide are definitely functions of the parts of the turbo, but I understood the pressure measurement to mean that it's atmospheric coming in, and 20psi over atmospheric going out.

    Is that totally wrong?
  16. I have a hard time believing it's 7hp for every psi, on every turbo on every set-up. WAYYYYY too many variables to just say that. I'd love to see how someone came up with that.
  17. I have a hard time understanding it too. In fact, I still really don't. But I think efficiency, volume and velocity all matter. A bigger turbo moves more air at the same pressure. It might be 20psi, but it leaves the system much quicker maybe? I'm really not sure but I'm 100% sure that 1 lb of boost does not mean the same thing on every setup.
  18. O rly? So my 18psi TDI engine which makes 90hp would make -36 hp without the turbo?
  19. hahahahahaha
  20. That was Hetzen posting btw....
  21. I wonder that myself. Seemingly SOME amount of power would be lost by having th turbo slowing down the exhaust. I'd be willing to bet it's a lot less than the blower would though.
  22. Indeed, but the power to drive the turbo is "recuperated power" and the power for the supercharger isn't. The backpressure you allways need is used by the turbo. The heat from the exhaust gases is also used with turbochargers and not with superchargers. Also superchargers seem to mee to have more frictional losses and are heavier aznd thereby not able to spin as fast as a turbo => top end power suffers from this i guess??

    If i'm mistaken please point this out.
  23. Wow. There is so much misinformation in this thread, it's not even funny.

    First. PSI is pressure. Pressure does not make power, does it?? The combustion of the air-fuel mixture makes power. The amount of energy released is directly proportional to the mass of the air and fuel combusted. The power produced is directly proportional to the mass flow rate of air and fuel through the engine. The pressure that the compressor delivers does not push the pistons in, does it?

    Anybody who's done their research or has experience knows that two turbos can make vastly difference power outputs at the same pressure.

    Second. A supercharger does NOT produce a linear amount of boost. Positive displacement pumps such as roots blowers (which are not compressors) are not sealed and as the pressure on the output end rises, it pushes air back through the lobes at a non-linear rate. A radial compressor is not sealed, period. Just because it spins at a constant ratio to engine speed does not mean boost is linear.

    Third. Hetzen, the size of the supercharger or turbocharger as well as a dozen other factors can completely change the shape of the torque curve. Further, it doesn't matter how much horsepower you make, torque is what spins the wheels and accelerates the car. The acceleration of the car is directly proportional to the instantaneous torque available to the wheels, at all times. If you are making 300 constant horsepower over a 3000 rpm band, then your available torque will be constantly decreasing and your car will accelerate at a decreasing rate.

    Fourth. Announcing that X psi will make Y horsepower is a sure-fire way to let everyone know that you have no idea what you're talking about.
  24. Yeah, I'm with ben. It's as if you people don't even realize what PSI stands - Poor, Starving Infants. I use Cambodians because I find they're the most efficient.

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