How exactly does a turbocharger work?

[VaSteve]

Yeah, I know it's probably a dumb question, but I honestly have no idea. I understand the basic concept of a regualr engine, but then you have terms like "apiration" and "boost"? Plus I know you can add turbochargers to "normal" (non-Porsches), how the heck do you do that?

Help me out people, what the heck is it?

Thanks
Steve

[69 911s]

Steve,
The only dumb questions are the ones you don't ask, that's the great thing about this board.

The turbo is a small (depending on the application) fan wheel in the exhaust driven by the exhaust gas as it flows by. On the other end of this shaft is another fan wheel that drives (and thereby pressurizes) the intake charge in the intake manifold for increased, or boosted intake charge into your cylinders. That's the simple configuration, which as you can imagine requires different exhaust and intake manifolds and routing. Also, since the intake is now pressurized, instead of pulling a vacuum, you have to relocate vacuum operated accessories like the brakes and distributor advance upstream of the impeller.

Now ask about intercooling!

Fellow NOVA
Holder Trumbo

[911nut]

Here follows a (very) simple explaination of turbocharging.
Engines are air pumps. The more air/fuel you can get into and out of the cylinders, the more power you can make.
Normal engines pull in charge (air and fuel) when the piston travels down in the cylinder (kind of like a syrenge when you pull the plunger back) so the limit to the charge volume is the volume of the cylinder and how many times a second you do this.
So, if we could force more charge into the engine we can get more power for a given displacement. There are two ways to do this; add nitrous or use a supercharger/turbocharger.
The turbocharger is a combination turbine (connected to the exhasut flow) and a compressor hooked together on a commom shaft. The exhaust gasses spin the turbine which, in turn, spin the compressor. The comperssor shoves a lot more air into the cylinders (the fuel delivery system must be calibrated to add more fuel to maimtain the proper air/fuel ratio), hence, more power is produced by the engine. The boost pressure is the maximum pressure the charge is being shoved into the engine at.
There are lots of issues that go along with turbocharging like charge temperature, fuel delivery calibration, turbo lag, ect.
I'm sure the experts will now chime in............

[s_wilwerding]

This is a very simple explanation, but I'm sure someone else will jump in.

All engines, at a given temperature and RPM, have an "ideal" mixture of air to fuel, which for most modern engines is around 22 to 1 at warm idle, or thereabouts. Most people think that to make more power out of an engine, you just add more fuel. However, this just makes the car run rich and puts the engine out of its "ideal" range, which actually hurts performance rather than helps. So, the trick is to add both more air and more fuel in the "ideal" ratio so that an engine can make more power.

The only way to add more air to an engine is to compress the air. That's what turbochargers and superchargers do. The difference between turbochargers and superchargers is how they are powered. A supercharger is basically a compressor that is run via a belt off your engine (like the air conditioning compressor, or the alternator). A turbocharger, on the other hand, is like a windmill that is powered by exhaust gases. Turbochargers have the advantage of not sapping engine power by running on a belt, but they have the disadvantage of not working until the exhaust gases flow fast enough to adequately power the turbocharger. For instance, in old Porsche Turbos, The turbo doesn't kick in until around 3,000 RPM - this is called turbo lag.

In answer to your other questions, aspiration refers to how the engine "breathes". If your car doesn't have a turbo or supercharger, it is said to be "naturally aspirated." If your car has a turbo or supercharger, it is generally referred to as "forced induction" or "blown." Boost is the amount of compression that a turbo or supercharger performs. Boost can be measured in PSI (pounds per square inch) or in bar, which is atmospheric pressure (roughly ~14 PSI). If you have a turbo that runs at 1 bar, that means that the turbo is compressing the air to roughly 14 PSI.

Adding turbos to non-turbo cars can be done - it just comes down to plumbing the turbo into the intake and exhaust systems. However, a "normal" Porsche engine is not designed for the stresses of turbocharging, so you generally don't run much boost - only around 5 PSI.

I'm sure someone else will chime in and fill in the holes I left out.

[89911]

http://auto.howstuffworks.com/turbo.htm

[azasadny]

Thanks for the info guys, I was wondering the same thing but didn't want to ask the question! Good clear explanation and no "you're stupid" comments. You guys are the best!

[VaSteve]

Originally posted by azasadny
Thanks for the info guys, I was wondering the same thing but didn't want to ask the question! Good clear explanation and no "you're stupid" comments. You guys are the best!

I'm glad I asked for us both! Pelicanheads are really great people willing to share knowledge!!!!

However, does the knowledge sharing subside over the summer while we're all out driving, AXing, doing engine drops?

Have a great Thanksgiving, everyone!!
Steve

[johncj8989]

It works very much like the highly popular eRAM. I think I remember seeing a thread on that subject.

LOL. Sorry ...couldnt resist.

[azasadny]

Steve,
I'm on the BBS year-round and I haven't noticed any drop-off in helpful posts during the summer (driving season).

[coolbreeze]

so what is super charged then? same as a turbo sept the presurization is created by a mechanical or belt driven

[89911]

http://auto.howstuffworks.com/question122.htm

[Hugh R]

Cool

yeah, thats basically it, belt driven, but you get boost (I believe) all the way up from idle. I think some superchargers have a magnetic clutch like an A/C compressor, but I don't know when the clutch kicks in.

[1fastredsc]

Superchargers are turbochargers that are belt driven off the power of the engine. Unfortunately, yes they always create boost without lag, but they also are less efficient because it takes power to make power with a supercharger. The turbocharger uses free exhaust power that usually just gets waisted anyhow.

[beepbeep]

Superchargers always provide boost...which is good for full throttle but you don't want boost while driving in town, so all that boost is just recirculated around and around on most clutchless installations, lowering efficiency even further.