Turbo vs Supercharger

[bjdm151]

is that a mustang with wings and fangs or should we just call it a "RICESTANG"

[Zgringo]

If I may I'd like to clear up some statements made hear that are some true, some false and others old wives tales. I have been personally been involved in supercharging and nitrous for many years, before some of your parents were born. I have a degree in metallurgy and aero. engineering. I have or have had a few world records on the Salt flats. Made a few record passes at different 1/4 tracks, and at present have the 3rd recorded fastest street 300Z and in the top 10 last year in the Pro Import class. With that lets get to the subject matter. And please no pissing contest. Lets deal with facts and not personal tastes.

Both turbo's and root or screw compressors are superchargers, the difference being one is exhaust driven and the other engine driven. From this point on both well be refered to as superchargers. Both have been around longer than me. Both have good points and weak points, but both do one thing, stuff more air into the engine, whereas increasing the compression ratio and increasing the VE (volumemetric effinicy) of the engine. In the begining both were very crude but engineers spent more time on development of the turbo's than the root's so the turbo's become more advanced than the root's.
A few years after the computers came out all that started to change. You as the comsumers demanded better cars with more efficient engines so the engineers were back at the drawing boards working on new designs and the screw type supercharger was born. Today we have turbo's with new designed compressor blades beyond anything ever dreamed of a few years ago. Screw type compressors that weren't even born yet, and engines begging to have one installed on them.
Some things you need to do before installing one is to do some research and deside which one best fits your needs. One thing to look for is the Delta Temp. of the unit and its installation. I'm not going to list everything here for space reasons, but well list a few good and bad points.
Turbo's run extreamly hot, whereas screwtype's don't.

http://www.chimera.co.nz/300zx/

Turbo's use less engine power than engine driven superchargers.
screwtype superchargers don't have turbo lag.
Engine driven superchargers are easer to install than turbo's.
Now this is just a small list and I'm sure you all can add more to it, but we need to move on.

Without getting into cams, porting, exhaust systems, nitrous and the likes, compression is one of the most important things in making power in your engine. A 16:1 compression ratio is just about the limits we have for the fuels we have today. With the computers we have now this is easy to do on a street car.
Why is this compression so important, well it's the amount of compression placed on the fuel/air mixture at top dead center, and the amount of force placed on the piston pushing it down making power.
Now were giong to take 3 engines and the only difference is compression ratio.
engine #1 16:1
engine #2 10:1 with 10# boost
engine #3 8:1 with 16# boost
What is the different of these 3 engines flywheel HP? None. There all running about 16:1 compression ratio and have aprox. the same HP

http://www.goodvibesracing.com/Compression%20Ratio.htm

Now most high performance cars have 8:1 pistons and turbo's with 8-10# boost so in reality the engine is a 12.5:1 engine, and everyone trys to get rid of the turbo lag. Sorry, no such thing turbo lag.
A 8:1 CR engine just don't have any power at low RPM till the turbo puts enough air into the engine to raise the CR to 12.5:1, then power is there.
The screwtype supercharge being a postive displacement compressor keeps the 8:1 CR engine at 12.5:1 all the time and don't have the so called turbo lag. Thats why people say screwtype superchargers don't have turbo lag.

Now if you really want to have fun, but I warn you be careful and go in small steps, play with more boost and your timing with some fuel that can handle a CR of 25:1. To do this you'll need to have a engine strong enough to handle it, but you can make somewhere in the area of 1000HP per liter.

http://performanceolds307.tripod.com/id9.html

If you think I'm full of shit, lets talk about it and make me prove it, but please before you beat me go to the sites and read them.

Albert

[P10DET]

Originally Posted by Murda C

the reason a turbo usually gets hotter boost is because the turbo is driven by exaust, which is really hot. this heats up the turbo, which heats the boost, already adding to what nissanfanatic said about compressed air.

Geez.

Turbos heat up the compressed air less than a supercharger.

Once again, efficiency is defined as the delta t (temp) between the inlet and the outlet of the compressor. Turbos are more efficient.

For those who actually want to learn something about this subject, read Mike Kojima's "Suck, Squish, Bang, Blow" series of articles in Sport Compact Car (back when that magazine actually had high quality tech articles).

[P10DET]

Originally Posted by Zgringo

Both have good points and weak points, but both do one thing, stuff more air into the engine, whereas increasing the compression ratio and increasing the VE (volumemetric effinicy) of the engine.

Turbos and superchargers DO NOT do anything to the compression ratio of an engine. Compression ratio is a static measure regardless of VE. Internal cylinder pressures are changed with changes in VE but compression ratio always remains constant.

And for those who may want to talk about dynamic compression ratio, this does not exist either. What we're really talking about is changes in VE.

Originally Posted by Zgringo

Turbo's run extreamly hot, whereas screwtype's don't.

I guess that depends upon what you define as hot. The housing may run hot on a turbo, but, properly sized, a turbo is more efficient than any supercharger, and by definition, the delta t is lower with a turbo.

[runningmole]

Zgringo-I'd love to see back to back dyno pulls of a non-intercooled screwtype blower. 2nd pull is going to be way down on power. Those things get VERY hot. Intercool or water/alcohol inject them, and it's a different story.

Also....my engine has 8.2:1 compression, and makes PLENTY of low end power. It's going to make more once the blower is on *evil grin*

How can a supercharger have turbo lag?

[runningmole]

Originally Posted by Damious

well superchargers have no lag, so they would be better for autocross IMO, but turbo's can have more power...

super's u will lose alot of gas with them since they are working all the time, turbo not really at all... since they dont kick in in low speed areas (like driving around town).

also i hear superchargers are easier to install... but yes more pricy...
turbo is good for top numbers...

but like i said, i think if ur goal isn't all out power, and u dont care about losing to much money... supercharger is where i think u want to go....

the supercharger will lose power cus its pully driven (plz dear god dont get a Centrifugal Supercharger, if ur planning on that, turbo is definately a better option.

roots blowers are good but run pretty hot.

Centrifugal superchargers are not always making a drastic amount of boost. It's not going to waste gas (unless you're a lead foot or have a really wild combo). Why are superchargers bad for auto cross? Do you auto cross? Have you ever? The only time I'm at idle is at the start. Other than that, my motor is revving above idle. Properly set up combos will NOT be turds for their specific application, or any aplication. Properly sized turbo(s) for your application can make power from idle to redline, no lag time. I think you need to stop thinking of dyno-queen Supras when you hear the term "turbo." I've yet to see a supercharged vehicle make more power NA than it did boosted. Yes, it does take power to turn the S/C but it responds by making MORE power.