SnowmanSteiner

I am not sure where to post this so I am putting it here hoping that enough people will see it and use it. This is some advice that I got from Pettit racing.

"Start the car and immediately poke the throttle to prompt the kick-down. (Pettit actually recommends turning it off for a couple of seconds immediately after it catches to allow freshly pumped oil to seep into the bearings while they're loose, then restarting.) A lot of wear occurs during that 30 seconds or so at 3,000 RPM. It does this to warm the cat to operating temp sooner, but at the expense of your bearings. Within a minute, start driving. Warm up the car under light load, not sitting idling in your garage. Wait until the temp gauge shows normal operating temp before going above 4,000 RPM or above 5 lbs boost (see boost gauge below"

Hopefully this will help you guys who have turbos. And help ensure a longer life for your turbos.

Project84

That is one reason why I decided to go for a supercharger on the engine I'm building. Turbos wear a lot easier. I found out that the shaft on the compressor in a turbo spins up around 30,000rpms. Plus the extremely critical warm up/shut down procedure is not really what I want in a sports car. Just my $.02

SPOautos

So a supercharger doesnt use oil? What does it use?

STEPHEN

Project84

it uses oil, but you don't have to baby it on start up and shut down like a turbocharger. Both have their ups and downs, just depends on what you use the car for. Some people do auto-x, so drag race.

duboisr

turbos turn faster than 30000 rpm ,any way I was told to drive away slowly also, this heats up the trans, and rear end also. why heat the motor sitting still then speed away with a cold trans and rear end.

Project84

I know, they turn like 130,000 to 150,000. I left out the 1 and by time I realized it, I couldn't edit.

Piranha

Turbo timers aren't that complicated.. the killing the cold warm up just takes a blip, and driving slow for a little while. It isn't that big of a deal.

PJ RX-7

Powerdyne doesn't use oil. But you probably didn't know that, cause they're pretty much for V8's

Check it out: www.powerdyne.com

FC3S DreamS

turbos have the most power potential... top end, but some loss of lower end torque... superchargers have a constant stream of boost going into the motor because they are belt driven intstead of exhaust driven... both are excellent tools for more horsepower... it all depends on the application youre using it for...

Damnfuct

superchargers don't make any kind of REAL boost (compared to turbos anyways), sure you can get your 6 psi at your 2000 rpm, but what happens at redline? overspin your supercharger and your thermal efficieny goes to ****, not to mention horror stories i've seen of some guy running to big of a pulley on his supercharger.. the rotating parts overheated and expaned, gouging out the compressing chamber. i'll bet you can still make him go "ooo" and make a "ooo" face if you mention metal shavings in his engine and not to mention a screwed supercharger.
Because SC's are spun by the engine, they are at a constant ratio to the engine (related to pulley sizes).. turbos rely on exhaust energy.. cut the exhaust energy and you'll cut the turbo rpms and flow rate.

Oh yeah, turbos are spun by 'wasted' exhaust energy and not by some parasitic drag on the engine (aka "free" horsepower)

Project84

Nothing is free. It takes a lot less power to blow through a turbo than to crank a supercharger, but it isn't free power. There are pros and cons to each system.

Damnfuct

i see quotations there; do you see quotations? You do know what the quotes signify, don't you? Go roll your eyes elsewhere.

Turbos don't take all their energy from the mechanical motion of air being pumped out of the combustion chamber by the rotor face or piston. I believe this is a common misconception that i had at one time.. most of the energry is obtained from the hot exhaust gases trying to expand out of the manifold (turbos don't just glow red-hot because it's 'cool' or 'tight'). Also, when you start getting onto the boost the combustion chamber fills with more air/fuel than it could fill under normal atmospheric conditions.. Then the combustion happens and because there is more air/fuel burning, there is more pressure on the piston/rotor face (increased power). When exhaust cycle happens, there is still some pressure on the rotor/piston face.. (we'll talk pistons for an easy example) think of it as a 12:1 compression ratio on a 8:1 compression engine.. the piston is at its bottom dead center, but there is still more air/fuel and not to mention a higher ambient pressure inside the cylinder wanting to push down.. exhaust opens and it comes out of the chamber, feeding the turbo more energy.. Hence the reason why big turbos come on with a thump (exponential increase.. their own force-feeding causes an inefficiency in the engine which the turbo lives off of, allowing the turbo to cram more air in, giving it more 'waste' energy, etc).
Most of the energy a turbo feeds off of is "scavenged" off of 'lost' energy. Some energy is from the pumping of air out of the cylinder, but that's negligible compared to horsepower/torque increased and is dwarfed very much by the power required to spin a supercharger under boost conditions.

Then again, that's my 2 cents.

Damnfuct

and another thing.. "free" is a relative expression,
And relating turbos to superchargers, a turbo's energy source is generally "free" :P

Edit: and another thing! if turbos ran off the mechanical motion of pumping air out of the cylinder, how do you explain those 'jet' engines they make out of a turbo and a combustion chamber (like teh 'jet' mr2).. Intake compressor compresses air through a pipe into a cylinder, fuel is burned in teh cylinder, hot gases go from the cylinder through tubes to the turbine wheel and out the back.. Work is done by thrust only. These are similar to Jet engines, but are not all one unit (i guess more primitive) There's NO pumping action by something like a piston in that engine at all, sure you can say the compressor pumps air into the cylinder, but what pumps the air out? Compression is an "elastic" process.. energy in is almost equal to energy out, so basically you get 0 energy at the end between the negative energy used to pump air in, and the energy gained from pumping the air out the turbine. Where does the thrust come from? Sure, there's the energy of the x psi the compressor put into the cylinder, but it's not like that x psi makes **** all of a difference compared to the total energy released out the turbine

peejay

The fact that EGTs significantly go down after going through the turbine signifies that otherwise wasted exhaust energy is being recouped by the turbocharger. Yes they do add backpressure BUT on the other hand the exhaust gas pressure is significantly higher than a N/A engine anyway (because there's more gases in the chamber to start with) ALSO with a turbo turbo setup the intake manifold pressure is HIGHER than exhaust manifold pressure.

Superchargers are not "bad" but turbos are much more efficient because they use energy (velocity and heat) that would otherwise be literally thrown away out the exhaust pipe. And rotaries have more than enough exhaust energy

Project84

1. I know how a jet engine works. I'm an aircraft mechanic. I forgot more about jet engines than you will ever know damnfuct.

2. No matter how you try to word it, the fact remains that the exhaust gases expelled from any engine requires work from that engine to push the gases out. It may be an very insignificant, almost immeasureable amount of work, but it is still an amount of work that is subtracted from the total output capacity of that engine. Placing an aditional object in the path of the exhaust gases (such as the turbocharger compressor) is going to require more work. The turbocharger in return, injects more are into the intake, allowing more fuel to be burned resulting in more power. This is perpetual motion. The same thing happens in the jet engine. The turbine that you mentioned has a shaft connected to fans in the front. The exhaust blows through the turbines, the turbines spin the fans drawing in more air. In both cases of a turbo car, or jet engine, the work spent on expelling the exhaust is multiplied into the amount of intake not normally attainable.

3. As I have said at least twice in this thread, a turbo and a SC each have their advantages and dissadvantages. It depends on the application of the car as to which one the driver prefers. You gave your 2 cents, and there is your change.

Damnfuct

I don't know who you are, or where you work; i'm not a stalker
I just explained it in terms so if you WEREN'T an aircraft mechanic, i wouldn't have to go through another post explaining it.. i never said ANYTHING about me knowing more than anyone else.

There comes a point in life where you just have to say "close enough." if you finished a road course in 12.999999 seconds, wouldn't you just say "close enough" and say 13? What significance does 0.000001 seconds have anyways? Probably the significance of always wanting to be correct

Of course the turbo draws energy, and some IS infact taken directly from the engine, but the majority (majority means greater than but not including 50%, by the way :P) is drawn from EXHAUST gas heat.




Perpetual motion? Eventually the fuel source runs out :P
Perhaps you meant "continual" ?

It's not multiplied at all.. Energy does not come out of no where. Lets say the turbine/compressor is 100% efficient and the energy lost by the mechanical pumping of the air out of the cylinder is perfectly regained by the turbine pushing air into the intake, then you get 0 (yes ZERO) energy increase from the engin. So "where does this extra energy come from" you ask?
why, the heat from the exhaust.
And what is exhaust, you ask?
Well, dictionary.com describes Exhaust (noun), def'n 1a as:

The escape or release of vaporous waste material, as from an engine.

And what is waste? A quick look at dictionary dot com describes waste (noun) def'n 4a as:

An unusable or unwanted substance or material, such as a waste product. .

So obviously the engine's done with the gas if it's opening the exhaust valve. So where does this energy go, does it turn into a jet plume and propel the car forward?
nope.
Well, is there a turbine that's connected to the drivetrain somehow?!
no way.
Well where is it going?
Well, the energy is creating work on the atmosphere, by raising its "H" i believe (you'd know if you are a jet-engine guy). That's a good use of that energy. Maybe you like taking power from your engine instead of the exhaust, but i don't.. Maybe if was autocrossing like you said. But if i wanted torque i'd get a more torquey engine and turbo it :P

I didn't say superchargers didn't have their ups.. I've just supported turbo throughout the thread because besides constant pressure or low-rpm boost, superchargers are pretty much inferior to turbos. To me, supercharger's ups aren't outweighed by their downs.. especially when considering a supercharger that replaces the intake manifold and goes straight from the supercharging mechanism to the valve ports.. You can't even intercool it, so A) you've got a crappy thermal efficiency, and B) you can't even intercool it to reduce the charge temperature. Talk about a lose/lose situation; you couldn't run high boost if you wanted to/fi the supercharger would let you!

Project84

Ha Ha, the .000001 does matter cause if one person finishes with a 12.999999 and the next guy has a 13 flat, who wins?

It is perpetual motion. Jet engines are the same way, and they will also eventually run out of fuel. But you got the idea that I was trying to illustrate so it isn't a big deal.

Energy doesn't come out of nowhere, but it is changed from potential energy to kinetic energy. Pumping more compressed air into an intake with a turbo, SC, or even NOS for that matter, greatly increases the available potential energy at a fraction of the cost of the kinetic energy when the spark plug fires.

Your example doesn't make any sense. If the engine was 100% efficient, there would be no heat. Heat is a form of energy loss, which would be less than 100% efficiency. There would be no air out of the cylinder. A 100% efficient combustion would have no by-product, or no exhaust gases. Ever molicule would be 100% consumed.

Damnfuct

Project84

Well, if you want to make up hypothetical situations, lets say there is breatheable oxygen on the planet Saturn. Then we can auto X RX-7s around the rings.