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Ntseg Muag!
SRP MY00 Subaru Impreza 2.5RS
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Discussion Starter #1
as of now i don't really know that much about turbos yet...all i know is that there are quick spools , mid-range, and high range turbos...they help compress air before it enters the engine to help increase power......i was lookin at turbonetics turbos and was lost just lookin at all the names and numbers......
 

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Ntseg Muag!
SRP MY00 Subaru Impreza 2.5RS
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Discussion Starter #2
Does anybody know anythign bout this? please i must know so i can decide on a turbo when the day comes...
 

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what do you want to know, exactly? you could write a book about turbos in general (and someone has, its called Maximum Boost). i'll give you a basic overview.

a turbo is nothing more then an air compressor, just like a supercharger. the thing that makes it really cool is how its powered. as you no doubt know, it takes work to compress something. work means you need power, so where does the power come from? in a supercharger, it comes from the crankshaft. this isn't very effecient since you're using the supercharger to turn the crankshaft faster, but then you use some of that extra power to keep turning the supercharger rather then the tires, which is the ultimate goal of course. what a turbo does is rather ingenious. in most engines, approximately half the energy produced by combustion goes out the exhaust. not very effiecent. what a turbo does is use all this wasted heat (energy) to compress air to feed back into the engine. so it produces no parastatic drag on the engine like the S/C and it makes the engine more effiecent all the while boosting output. of course, since it needs a good flow of exhaust gases to spin it, it requires the engine to build up a bit of speed to start making boost. this is called turbo lag. as turbos get better and better, lag keeps getting reduced. how much lag you have is directly proportional to the flow limits of the turbo. there are other factors as well, but this is an overview ;) basic rule of thumb is the bigger the turbo the more peak output but the more lag as well.

now that you understand what a turbo does (hopefully), lets look at how it works. basically, a turbo consists of 3 main parts. first, you have the exhaust housing. this is where the exhaust from the engine enters (and exits) the turbo. basically, think of it like a hydoroelectric damn. there the water rushes past and the force of the water turns a wheel. same deal here, except the water is exhaust gases :) the flow of the exhaust basically turns a wheel/fan deal which is attached to a shaft. this shaft leaves the exhaust housing and goes across to the air inlet housing, getting a healthy dose of oil along the way. basically, the shaft, using energy provided in the exhaust housing, turns an impeller. this is what compresses the air. the air then goes to the engine where, combined with more fuel and some proper spark timing, you make potentially gobs more power.

ok, there you have the basic theory and mechanics of a turbocharger. now i'm going to talk abit about some of the more important details for your average enthusiast. stuff like impeller shape, shapes and sizes of housings, types of bearings on the shaft, anti-lag, etc are not going to be hit on. Instead, i'll tell you about the things that often come on a turbo kit and why they are important.

first up, lets do the wastegate. every turbo has one and this is the little puppy that keeps your engine from blowing up (hopefully). basically, its this little door on the side of the exhaust housing on the turbo (generally). this door is held closed by a spring. how strong this spring is determines your boost (amount of postitive manifold vacuum produced, measured in PSI in this country). basically, the turbo is busy compressing air. the more exhaust gas the faster it spins. a good turbo can spin in excess of 100,000rpm. this can compress quite a bit of air. more air then your engine/fuel delivery system can handle. so to control the maximum amount of air being sent to your engine, you have a wastegate. say the spring is overcome at 7psi. once that amount of boost has been made, the wastegate door opens, allowing some exhaust gases out of the turbo, slowing it down. once its below 7psi again, the door closes. this maintains a maximum boost level.

next up, the intercooler. all you have to do is think back to the HS chemistry class and remember the ideal gas law: PV=nrT. that says it all. as pressure (boost) increases, so does temperature. things get hot real quick with a turbo. really hot things blow up engines. bad. very bad. so to counteract this, most turbo systems use an intercooler. this is very similar in design to a radiator, except that often its air to air instead of air to water, though not always. basically, this is what the hoodscoop is for ;) hot air from the turbo flows through the iintercooler and cold ambeint air flows over it, dispitating some heat along the way.

by-pass valve. also known as a blowoff valve (BOV). this is the thing that goes "psst" in the Fast and the Furious when they shift. basically, even though you let off the gas to slow down or shift or whatever, there is a delay in the turbo slowing down because of exhaust gases still flowing to it and inertia mainly. so its still happily compressing air while none is actually flowing into the engine because the throttle is closed. uh-oh. what happens is the air will basically stack up on itself and actually bounce back down to the turbo. this is very unhealthy for the turbo. so what often is done is a BOV is added near the throtlle body. when the throttle closes, the BOV will open, venting off extra air so it doesn't stack up. granted, most BOVs in the import scene are designed more for auditory aesthetics then functionality, but to each his own.


for more reading, you can't go wrong with How Stuff Works
 

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Ntseg Muag!
SRP MY00 Subaru Impreza 2.5RS
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518 Posts
Discussion Starter #4
ohhhh...alright then.....thanks for the help.....
 

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great info, thanks. now how to apply that. so I've got a 2.5L SOHC and would like to go turbo. What's the best route while still trying to be somewhat economic?;)

--eric
 
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