how a turbocharger works
 

Hi guys... i've read www.howthingswork.com and all that other crap... stuff is just too hard to understand. I would like to learn exactly how a turbo works. I know the basic stuff like what spools it, and it's function as far as "forcing air" but other than that... i have a hard time comprehending how this thing makes soo much power.

For all the technical ppl, scott, dean, etc etc.. i'm sure you guys have a GREAT explanation for the process.

I've always had this question but have never been able to fully understand how it works. Hope i learn as a result of this thread.
thanks

mike

Re: how a turbocharger works
 

Well, sounds like you already know how it works. They're pretty simple devices. Exhaust gas spins the turbine -> turbine shaft spins the compressor -> compressor pressurizes the intake air -> compressed intake air is denser -> the denser air results in more complete fuel combustion in the cylinder, and consequently more power, when the sparkplug fires. Easy. :mrgreen:

I think he was going for somthing a little more dramatic? Such as maybe whats the best combination of machanics? Oil vs Water cooled or both? Ball Bearing vs Twin Scroll or both hehe? Does size really matter with the right turbine and houseing? I could be way off but if we are going to get a good Tech out of our next turbo purchase those would be some of my questions. :D

Like Austin said, there's basically two "fans" inside a turbo. One fan is in the exhaust stream, so the flow of exhaust makes it spin at a rediculously high speed. The other side of the turbo had a fan that compresses the intake air.

So when te exhaust flow is fast there's more compressed air entering the motor. And more air = more oxygen, and it's the exploding of the oxygen that makes power.

Like Mike was saying, because there are two different fans in the turbo, there's an intricate balance to be made between the sizes of the fans in relation to the motor. You can achieve different results by using different sized compresser and impeller wheels. I'm not privy to the details (it's over my head as to exactly how it all works out) but in general a smaller turbo needs less exhaust to spin up, so a smaller turbo has less lag, however it can't flow a lot of air so it limits top end horsepower. While a larger turbo can flow a lot more air so it's goot for big horsepower numbers, but it takes a long time to spin up so there's a lot of lag.

well said ths Scott........thx

well said... i knew most of what you said scott... i was more interested about interchanging the sizes of the Compressor and Impeller wheels, as you said, different results would be achieved if they were to be swaped with say another turbo. (i dont know if that's possible, however, i am pretty sure it is) I was reading about a WRX owner messing with the compressor wheel of a garrett gt30R turbo and i'm not too sure, but, i think he swapped it with a different turbo. (Maybe a t04) although i'm not exactly sure.

He didn't post any results so naturally, i had a few questions. :D

(sorry i couldn't get back to the thread sooner... been a little busy...)

my car goes faster after 3000rpms...

and I like it.

Well said. :D

I think one of the common things that confuses people is the use of the word fan. They often think of their radiator or house fans. Most people have little or no experience with turbines or even cetrifugal fans.

This is why you often get questions like, why not use electric fans for blowers...

Ok, this is oversimplified, but...

Lets do some math... a 2L engine running at 4000RPM sucks in about 4000L or 141 Cubic Feet of air per minute. This is an incrediable amount of air. Baically, a box of air 5 feet x 5 feet and just over 5.5 feet tall.

The turbo compressor not only moves this volume of air, but can maintain a positive pressure of 15PSI or so in the intake manifold while the engine gobles up this air.

This doesn't sound like a big deal, but maintaing this level of pressure would be like trying to blow up an air matress with a hole in it the size of your fist.... Not that it is the same technology, but it takes a big 50lb shop air compressor to move 17CFM @ 90PSI

So what does this mean? Well, if the cylinders on a NA engine are normally filled with air at say 5-10PSI, and the turbo can fill them with air at 15 PSI, in theory, you could see 50 to 100% more air and fuel to burn. Is there a corresponding 50-100% more power? Here are some VW specs, you be the Judge...

2.0L 115 horsepower, 122 lbs-ft torque, 4 cylinder, in-line, gas

1.8T 150 horsepower, 162 lbs-ft torque, 4 cylinder, in-line, 5V, turbocharged, gas

1.8T 180 horsepower, 173 lbs-ft torque, 4 cylinder, in-line, 5V, turbocharged, gas.

Not sure if that helps, but it might...

damn..... :shock:

Thanks Dean that adds another part of information :D

I like teh math......hehe :D

Dean - I obviously am sold on the idea of a turbocharged engine in a car. My thought is why aren't more engines offered this way?

Franz

Usually emissions. Just like a high-displacement car, you're burning more fuel and air, which mean more pollution and lower gas mileage (actually turbos are better for mileage than displacement since you're usually off-boost when cruising).

Pretty much *every* disel motor sold these days is turbo... so the technology is definately being used, just not so much in gasoline motors.

On top of emissions stuff, turbocharged motors are just more complicated than NA motors.

When done right a turbocharged motor is much more efficient than a N/A motor, so it's actually best for gas mileage.

Right. That's why my EJ25 (which gets poor mileage for a car in it's class) gets better mileage than an EJ20. :)

Maybe the more accurate statement would be "When done right, turbocharged engines can get better gas mileage than equal power N/A engines when just cruising".

:)

Your strange Japanese engine codes mean nothing to me. :wink:

Okay let me rephrase. My non-turbo, large displacement motor gewts better mileage than the small displacement turbo motor, in spite of my car having 15% shorter gearing. :)

This is what I was getting at.