How reliable are turbo engines?

He isn't, he's just got a hard-on for me. Or he's embarrassed that I actually know more about this subject than he does, and is covering for it.

I dunno.

This information is available by typing a few things into the search line in Google. Heck, the Wiki entry isn't bad. A little long-winded, but the basics are there. Including wastegates and turbo size considerations.

You'd think before shooting off his keyboard, he'd at least look up

*something.*

:shrug:

E.P.

I have no idea. I do know that the turbo runs off the exhaust, and the exhaust is determined by both throttle and engine RPM.

No, I'm claimin that the exhaust amount diuffers mased on more factors than just engine RPMs.

No, not on a gas engine; you are more right for a diesel, but even then, as more power is produced (throttle opened) the exhaust flow increases.

I'm not a math wizard, but I know how turbos work.

Like I said, I'm not a math wizard. However, it's not hard to demonstrate. Have someone open up the throttle of a car while you hold your hand near the exhaust. You will notice an immediate increase in pressure that does not correlate to the increase in RPMs. Also remember that, as you open the throttle in the car, you let in more air/fuel, before the RPMS can rise at all. And as the throttle is held open, more air/fuel is still allowed into the cylinders; this is how gas engines accellerate. That increased air/fuel exits as exhaust, and makes the turbo spin faster. Isn't your MAF before the intake manifold? At the least, it's before the valves, if it's in the manifold. But the MAF will be downstream of the turbo's output, thus the air charge from the turbo goes through the MAF. And, of course, once it leaves the MAF, it eventually goes thru the exhaust; is there's a turbo there, it drives the turbo. Which then delivers air to the MAF.

Why should I attempt to cite anything? You never have in this thread, rarely have in others; and this post from you just proves everything I've written about you.

You'd have to drive over to Belfair/Hood Canal, where I will be busy driving around with some friends. I wouldn't want you to waste 4 hours of your valuable time.

FloydR

No. Exhaust volume is determined SOLELY by how much air gets into the cylinders. The cylinders' volume is fixed, and the more times you fill them, the more air comes out the other side. Period.

The calculation is thusly: One exhaust cycle every four revolutions multiplied by total engine volume is 500 x 2. 1000 Liters.

Prove it. BTW, 2000L exhaust at 4000 RPM. If you made a graph, you'd see it was linear.

You keep saying this like it's true. OK, prove it.

So far, I haven't seen anything that supports your opinion on the subject. But feel free to cite some reference.

And yet your making claims that require more than simple math to prove.

This is not physically possible. The volume in the cylinders is fixed.

14:1 air:fuel is the "perfect" ratio, and modern turbomotors use an MAF to keep it that way. But only so much volume will go into each cylinder.

The lag doesn't even take a half second at 2000 rpm.

The more exhaust there is, the faster the turbo spools. You don't get more VOLUME unless you fill the cylinders more often (higher revs.)

It is. It's right after the air filter, in fact. Before the turbo.

Which, like the rest of your stuff, comes from where? I don't know of any turbomotor where the MAF is after the turbo. But I'd be willing to learn - show me.

Now, before some pedantic Floyd comes in and grouses about the above, I have made a more simple picture of it than reality (the boost map is a complicated surface, not a curve or a line) but the basic stuff is there.

Bill, feel free to look this stuff up. It's out on the Web if you want to actually know, instead of imagining that you do. And if you find something that directly contradicts what I said, go ahead and post it. I'm man enough to admit when I'm wrong.

E.P.

You're making claims that are refuted quickly by a simple Google search. Or asking questions answered in the same way. And being an asshole at the same time.

So, if you you want to choose to not believe what I'm saying, fine. Anyone else can go to the Wikipedia turbocharging entry and see that everything I've said is correct.

That, and the fact you've been offered plenty of helpful instruction by other folks who also obviously know more than you.

How convenient. :snicker:

E.P.

If it's a gasoline engine, it has an air throttle that closes off the airflow at idle. When piston is at BDC the pressure in it is FAR less than atmospheric, which means there is FAR less air, density-wise, than there would be if the throttle is wide open. That's what a throttle does, after all; it controls airflow and therefore the amount of air entering the engine, and fuel follows that airflow. Even at full throttle in a normally-aspirated engine (no turbo or supercharger) the pressure will be below atmospheric due to the drag in the system. A diesel has no throttle plate; the throttle controls fuel flow. At low power settings very little fuel is injected but lots of air goes in. At high power settings, much fuel is injected, much heat and expansion is generated, and much of thatcombustion gas is still expanding when it leaves the exhaust. The released volume will be larger than cylinder volume. I teach this stuff in a College. Maybe you should start studying up on it.

Dan

You're making the mistaken assumption that one rev uses up a fixed amount of air, regardless of other factors. In fact, you're assuming perfect induction, ie. the vacuum gauge will read 0 at all times.

But the truth is that the throttle is a factor. If you are doing

4000rpm with the throttle shut, there is NO air going into the cylinders, and NO exhaust being produced.

1000rpm at half throttle takes in more air than 4000rpm with no throttle.

Now, suppose you open the throttle a little. You will get some air in the cylinders, but this amount is clearly a lot less than will get through if you had the throttle full open. (Otherwise the throttle would make no difference, which is obviously false).

This is reflected by your vacuum gauge, which will move up towards 0 as you open the throttle wider.

This math doesn't need any numbers. If the throttle is open wider, and the air pressure remains constant, then a greater volume of air moves through the air intake. This is why cars accelerate when you open the throttle.

[non sequitur snipped]

Of course, if you take it out of context, you can pretty much refute anything. And the snippet you replied to doesn't have much to do with your reply.

The throttle setting will determine the RPMs, which determines the total volume of gas going by the turbo. (Of course there are going to be times when that's not true, like during a shift when the throttle is closed, and the engine is still spinning. But the turbo really isn't doing any work there - it's just along for the ride.)

Now, if you want to talk about off-throttle periods (during shifts, for instance), then that's more of a special case than when you are using the turbo to do the work for which it was intended. And in this case, both the motor and the turbo "spin down" a bit as they freewheel. But you're not really filling the cylinders in that case, are you?

The statement above stands - the volume of gases you get out is determined solely by the volume of air that goes in.

That there are special cases in no way changes this fundemental volumetric physical reality.

E.P.

No, I'm keeping it simple to reduce the amount of typing. There are literally THOUSANDS of pages of reference material out there that explain it in exhaustive (pun) detail.

The fact that the discussion is moving into the realm of the pedantic in no way changes the fundemental reality of the situation - the more air you move past the turbo turbine, the faster it will spool, and the more air (and fuel) you can jam in on the other side. At higher RPM (except during shifts, or engine braking, etc.), there is more volume of gas going by the turbine, so it spins faster. Even suggesting that the turbo is independent of this is idiotic. Now, if we want to talk about the wastegate and how it functions under partial throttle settings, then that's another discussion. At steady-state cruise (in my car) the wastegate is open and the exhaust bypasses the turbine wheel. (mostly)

Now, that's a lot of typing, and for what?

And the turbo is doing no work, nor are you anything but coasting. It's relevant to the discussion of turbo function, how?

But you're not producing as much exhaust then as you would be half-throttle at 4000RPM. And in some cases, half-throttle won't even close the wastegate at low RPM. Thus you would be getting exactly the same amount of boost. (And a good thing - you don't want a lot of boost during shifts.)

And RPM would be steadily increasing. More air in, more exhaust out, more boost.

It does, especially if you are discounting the action of the wastegate. The throttle is not closed at 2000RPM, so saying something happens without providing numbers is just handwaving.

And it changes the volumetric relationships, how? Open the throttle (more air in), engine speeds up (higher revs) and more exhaust is made (spins the turbo faster to make more boost, to put more air in.) Cases like idle (no turbo work being done) and shifting (no turbo work being done) and engine braking (no turbo work being done) are all special cases that in no way invalidate the fundemental principles. The wastegate function, and design, do change things up. But I'm not going to type all that in for folks - DAGS. Or choose not to believe what I'm saying. That's OK. too.

E.P.

no, still not true. the MASS of air that goes out the exhaust it determined by the MASS of air that goes in. which, in turn, is determined by throttle opening and volumetric efficiency, among other things. And yes, a turbo (or other supercharger) can push you over 100% VE - that's the whole point of it. so the cylinder's volume really isn't "fixed" in the way you are trying to envision it.

nate

I can't say I've ever really noticed it on a 9000.

Graham

They are, even to this day reckoned to be one of Saab's finest ever ! And that's quite an accolade. And I've yet to get my hands on a full-blown 2.3 Aero yet.

These are great. They have excellent support in all the right places. The importance of good seating is vastly and very unwisely underestimated. It has a very capacious interior btw. Even you guys rated it as a 'large car' ffs.

Actually it's just simple depreciation. Because they're something of a specialist marque they devalue faster. I'm not complaining ! I don't normally buy new.

Graham

See the red line.

Graham

No, I have a turbo or two.

Actually, you'll find I'm right.

You're assuming that an engine has to 'modified' to be a turbo ?

Also, what kind of displacement are you talking about ?

I know.

Graham

Neither does a turbo. It simply provides a pressure above atmospheric.

Graham

Eeyore said in rec.autos.driving:

Well, hey, I'm glad you're happy with your ride.

Probably not powerful enough

It is a problem on more powerful models:

Again, too much power for a FWD.

Likewise !

Give a 9-5 Aero an outing sometime btw. You might like it !

Graham