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Turbochargers & Superchargers: Theory and Application

robertmcdonaldrobertmcdonald Posts: 1
edited March 22 in Porsche
Is there a clear "better" way of boosting your car (in the pressure sense of the term)? Are the losses of "turbo-lag" sufficent enough to justify going supercharger over turbocharger? Does it depend entirely on the car?

Lastly, if you think superchargers are better than turbochargers, why do so many sports cars (i.e., the 911 Turbo) use turbos instead of superchargers?

Thanks for your opinions!
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Comments

  • 8u6hfd8u6hfd Posts: 1,391
    Jag & Benz use superchargers.

    I believe there's no superior way. Both do its job, differently, with different characteristics of each.
  • jeproxjeprox Posts: 466
    i could be wrong but from what i hear/know...
    - supercharges are more expensive but you get less lag time. s/c is supposed to be much stronger too.
    - turbo's are cheaper but takes a bit longer to get you going. older turbo's are more expensive to fix and break down easily.
  • 8u6hfd8u6hfd Posts: 1,391
    Superchargers are crank driven, by belts. They don't really exhibit "turbo lag". A roots-type or positive displacement (Eaton)SC will exhibit a very linear powerband. Eaton SC is used by GM, Toyota (TRD), Benz, etc.

    Centrifugal SC shows more of a peakier powerband. THey also require a geartrain to spin it faster to be effective.

    Turbos are exhuast driven centrifugal compressors. With proper design, lag can be minimized.
  • hpulley4hpulley4 Posts: 591
    ...you suffer large fuel penalties and other problems with a jumpy car due to very high idle speeds. Racecars use turbos with no lag by always using enough throttle to keep the turbine up to full boost speed, even if you are in neutral. Most street car drivers don't want to idle at several thousand RPMs all the time. Dumping all that into the clutch on every start is bad for it, as is putting that many revs on an unloaded engine all the time. This is why those racing engines don't always last the whole race and why they need a lot of work between races if they do survive.

    Remember that neither system is a free lunch. You'll always get a more fuel efficient system with a naturally aspirated version. A SC that you can freewheel until needed is pretty much inert until you use it but while in use, much of the engine's power goes to the compressor instead of the wheels. You get more air through the system which yields more power in the end but the hp/gallon always goes down. The TC tries to be a free lunch by using the exhaust gases but it ends up being an exhaust restriction which hurts its efficiency. You get more power out of it but only at the expense of more fuel again.
  • 8u6hfd8u6hfd Posts: 1,391
    The WRX gets horrible fuel economy, for a 4 banger (something like 20/24 city/highway).

    The VW 1.8T & 2.0L on the otherhand, get identical gas mileage (24/30 city/highway).
  • hpulley4hpulley4 Posts: 591
    3 (yes, three) MPG according to an article on the racing team. 300hp out of 2.0L with lagless turbo won't get you an EPA award.

    The 1.8T gets the same mileage as the bigger 2.0L when you would expect it to get slightly better mileage in the same car if it were NA. They are not just turbo and non-turbo versions of each other either (1.8T is 5 valve/cyl for a start). The 1.8T isn't nearly as high-pressured as the Subaru 2.0 so it isn't as obvious.

    The turbo charger looks like a perpetual motion machine (using the engine to speed up the engine) until you see that it uses more fuel in the process.
  • The biggest differences are pretty much already stated. But to run thru them again.. a supercharger is run directly by the engine, usually by a belt. Superchargers spin at lower speeds (in direct relation to the engine's rpms, and at much lower rpms than turbos spin) and provide pretty linear power. Turbo's spin off the exhaust, and are geared to spin in upwards of 60,000 rpm's. The higher spin allows them to move more air (but also causes higher temperatures, giving rise to the benefits of an intercooler). Turbo's usually provide alot better high end than superchargers, but superchargers tend to have better low end. This can be compensiated for on a turbo by lowering the spooling RPM.. and using a wastegate to vent the excess pressure made at the higher RPMs. (Without the wastegate, trying to make up for the spooling speed would cause too much boost in the higher rpms). Also, you can use a NOS Turbo kit, which feeds nitrous at the lower rpms to get the engine up to spooling speed quicker.
  • armtdmarmtdm Posts: 2,057
    A GM 3.8L SC V6 with 240 hp and a Mitsubishi 3000GT 3.0L 320 HP V6 twin turbo

    No comparison. Sure the SC is smooth but oh so boring. There is nothing like those twin turbos kicking in and putting you back in your seat. The SC just doesn't seem able to do that, too tame and constant
  • 8u6hfd8u6hfd Posts: 1,391
    It's not really fair to compare the GM 3800 Series II supercharged to the Mitsu 3000GT VR6 either. They are tuned to perform in different markets (and the GM is also an automatic one)...
  • armtdmarmtdm Posts: 2,057
    It is really a difference of constant or smooth acceleration versus the kick of a turbop at 2500 RPM.

    Turbos subject to cking if not idled down properly so it is more of a hassle to drive then a SC, especially if a daily driver, shopping multiple stopts etc. But, most peopel do not idle down for a minute either
  • 8u6hfd8u6hfd Posts: 1,391
    For turbos, though a lot people for the aftermarket are more concerned about huge power gains (huge turbos which take a while to spool up), a properly sized turbo can have minimal turbo lag.

    For example the VW 1.8T has a very flat torque band, which (let's assume a 2001 1.8T in the Golf/GTI/Jetta/Beetle application) its torque peaks at 155 lb-ft at 1900 rpm. It stays in the near 155 lb-ft vicinity all the way to about 5000 rpms.

    Let's take another small car example: the WRX. Below 3000 rpm, the turbo is not generating enough pressure for that "kick". After 3000 rpm, you'll feel a huge kick in performance. This is a case of a more serious turbo lag.

    Twin turbo setups can have the same characteristics of either mentioned above.

    Twin sequential, can have characteristics of both mentioned earlier.

    For coking of the turbos, for most people, the idle down is not necessary. For customers of Volvo, VW, Saab, etc, where the vast majority will use it as regular transportation, the idle won't be critical (as long the oil is regularly changed).

    If you're racing constantly from stoplight to stoplight, or keep the engine constantly revved closer to redline, then the issue of coking is more problematic (and oil quality), and hence you'll need to idle down for a few minutes, if not try to install a turbo timer.

    So the real questions should be, which is better, turbo or supercharging for the following driving styles: light driving (point A to point B), moderate (some racing of engine is necessary), & balls to the wall?
    Right now we're trying to argue all aspects, but ultimately we won't get anywhere.
  • rezo00rezo00 Posts: 103
    First there are superchargers, which provide a linier increase in presure based on rpm (because of a real constant conection with the engine) engine spins faster so belt turns super faster.

    Next you can have 2 little turbo's or one big one...2 little ones always offer less lag for a set boost because of less rotational inertia then the 1 big turbine...so they spin up much quicker...also engine rpm dosent have to be as high to get them moving...As for fule economy they can be made the same as a super or even better...
    Intake air is hotter on a turbo because the exaust gasses heat the exaust section of the turbine and it is pulled through the metel rod (metel conducts) which connects the exaust and intake turbines. This is why new ones may be made of ceramic to reduce exaust/intake heat exchange...
  • fedlawmanfedlawman Posts: 3,118
    I've heard that turbos only last about 50,000 miles because of the high RPM they operate at.

    If this is true, wouldn't a SC be a better choice for increasing overall performance without sacrificing durability?
  • armtdmarmtdm Posts: 2,057
    Perhaps earlier Volvos etc had turbos go at 50,000 but now they seem to be as durable as the rest of the components. Of course in a Volvo that is usually 50,000 miles
  • 8u6hfd8u6hfd Posts: 1,391
    It just depends on high hard you use your turbo. It's mentioned earlier, to increase its longevity, allow the turbo to adequately cool by leaving the engine at idle for a few minutes (depending on how hard you flogged the turbo).

    Centrifugal S/C has power characteristics similar to a turbo. In fact they are the same, except being belt driven.
  • i dont know why you think volovo's crap out at 50 k miles. my girlfriends parents have a 760 turbo wagon with 180 k miles and everything is still original, even the turbo. h
  • armtdmarmtdm Posts: 2,057
    My opinion of Volvos has decreased significantly in recent years. What used to be a well built state of the art safe car is now a run on the mill luxury sedan built by individuals that take the entire summer off of for holiday. (try and get parts in August???) I know, that should have no bearing on the car.

    Just based upon bad experience with Volvos and IMHO there is more scheduled maintanance on these cars then Amercvian or Japanese.

    Overpriced purchase price, overpriced maintenance and overpriced parts.
  • you could be one of those crazy guys that use a supercharger and turbocharger. the supercharger runs up to 4k rpm then shuts off and lets the turbo take over.

    gives better low end response of the sc and the better high end of a turbo without the turbo lag.

    saw an mr2 with that setup.. it was damn fast
  • badtoybadtoy Posts: 368
    is that you can engineer one for ANY car. Much more difficult with a supercharger. There are many turbo manufacturers out there, and there are many shops with a lot of experience in turbocharging. Just don't go nuts with it, and you'll be fine.
  • andys120andys120 Loudon NHPosts: 16,739
    I put over 100,000 miles on a SAAB 9000 Turbo and experienced no turbo-related or engine problems. Most of it was highway driving but with a lot of commuter traffic.
    This was an early ('87) 9000 with no intercooler.

    2000 BMW 528i, 2001 BMW 330CiC

  • SPYDER98SPYDER98 Posts: 239
    I killed my first turbo at 70k.
    I used mobil one during most of that period and always warmed and cooled the car for a few minutes.

    On the downside, I beat on the car and ran higher than factory boost.

    So...I can't complain
  • Super charger

    Pros:
    Consistently good torque at all rev range
    No lag
    Relatively simple

    Cons:
    Sucks usable engine power causing poor fuel economy.

    Turbo charger:

    Pros:
    Highest power capability per unit displacement
    higher torque curve over usable engine speed
    improved fuel consumption compared to non-turbo of same power
    better emission

    Cons:
    Needs enpensive heat resistant ceramic material
    needs intercooler for optimum performance
    low torque at idle and near-idle speed
    turbo lag
  • Do the Veedubs (GTI, GOlf, Jetta, New Beetle) have intercoolers? If so, where?
  • isaaclisaacl Posts: 7
    I got a friend who just got a used 98 Mustang GT with the 4.6 (as do they all) Anyway, he started asking me about turbo and supercharging and all that. (A little too much Gran Turismo....thinks a turbo will put him up 120hp or so...)I told him to research it good and think about common NA V8 upgrades. Cams, rods, air intake-and exhaust and all will make a 4.6 perform better. I don't understand how people want this "easy" bolt-on turbo w/out understanding the extra stress on a factory NA motor. Like you can just push all that extra air through and not damage parts that were made for only a specific degree of performance........Am I wrong????
  • armtdmarmtdm Posts: 2,057
    The car I have came in two version one with a twin turbo. I noted that the compression ratio for the turbo is much lower then for the non turbo version.Apparently the higher compression with a tubo could cause severe damage, at least in my model.
  • andys120andys120 Loudon NHPosts: 16,739
    lower compression than their non-turbo cousins.

    2000 BMW 528i, 2001 BMW 330CiC

  • pantherburnpantherburn Posts: 15
    Check out www.miata.net

    Guys are getting astounding amounts of hp out of turbos, but lots of fiddling with computer/fuel curves, etc... - $$$

    SC - simpler, but much less power.

    Again, this is with reference to the Miata. Lots of pertinent info on the above mentioned site. Check it out. I would love to turbo my Miata, but it's still lots of fun stock - Zoom Zoom !
  • 8u6hfd8u6hfd Posts: 1,391
    Yes, they have intercoolers. They are located on the sides, if you look at the passenger side intake grille, you'll see the intercooler (remove the grille for better visibility).

    THe Audi TT, has them on both sides.

    The Turbo Diesels have the intercooler in the same location as the GTI, Jetta, & New Beetle
  • steverstever Viva Las CrucesPosts: 41,881
    Do all cars with superchargers or turbochargers require high octane fuel to prevent engine damage or premature death? Or is this just a way to bump up performance another 5+ percent to appeal to the person who knows they want a turbo or SC engine?

    Is there any difference in the designs that would require higher octane in a SC and not a turbo, or vice versa?

    Steve, Host

    Moderator
    Minivan fan. Feel free to message or email me - stever@edmunds.com.

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