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Turbochargers & Superchargers: Theory and Application

113 messages,  Last post on Jul 29, 2008 at 7:31 PM

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What is this discussion about? Performance Mods

Messages Page 1 of 12

#1 of 113 Which is better? by robertmcdonald

Jan 08, 2002 (4:06 am)

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!

#2 of 113 Depends on how you intend to drive the car by 8u6hfd

Jan 08, 2002 (5:37 am)

Jag & Benz use superchargers.
 
I believe there's no superior way. Both do its job, differently, with different characteristics of each.

#3 of 113 by jeprox

Jan 08, 2002 (10:08 am)

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.

#4 of 113 More tidbits here and there by 8u6hfd

Jan 09, 2002 (5:45 am)

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.

#5 of 113 no lag is possible but... by hpulley4

Jan 09, 2002 (11:48 am)

...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.

#6 of 113 For example...... by 8u6hfd

Jan 09, 2002 (1:28 pm)

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).

#7 of 113 Lagless Subaru WRC gets... by hpulley4

Jan 09, 2002 (1:42 pm)

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.

#8 of 113 Differences by rrossman

Jan 09, 2002 (10:10 pm)

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.

#9 of 113 I have one of each by armtdm

Jan 15, 2002 (7:25 pm)

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

#10 of 113 armtdm by 8u6hfd

Jan 16, 2002 (5:26 am)

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)...

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