How reliable are turbo engines?

If you only know how to stick the pedal to the metal then a Saab isn't for you !

Never heard of 'throttle control' ?

Graham

Last month I was in Pittsburgh, they have really short on-ramps, some of them going up hill, with stop signs to boot. No choice but to floor it in the second gear if you dont want to wait forever. Ever had to do something like that?

How many horses then?

True. But must have enough power also. Brand new Saabs exhibit torque steer, so they have that assymetry.

Seems to me that someone further up this chain is forgetting that when gasoline is misted, combined with air and ignited that it's energy is rapidly converted to other forms. Consequently the volume of air in that cylinder rapidly expands and the energy that doesn't drive the piston downward escapes either as heat through the cooling system or as exhaust. Expanding exhaust that is also pushed out by the piston drives the impeller.

He's also ignorant of the fact that air (unlike, say, hydraulic fluid) is a compressible (and therefore rareifiable) fluid, and simple piston movement has little to do with the volume of air (adjusted for atmospheric pressure) that will enter a cylinder. Nor is he accounting for the weight change of the gases; the fuel added to the air had to go somewhere. It experienced a chemical change and released its energy, but its weight is still there. There are so many variables it's not funny. And there are so many resources on the 'net it's not funny when someone won't look them up.

Dan

I'm far from an expert. But to ignore what happens to stored energy when spark is put to atomized fuel is surprising to say the least.

But, maybe he is on to something. Once you start the pistons to moving, all that compressed air should drive the turbo charger which should in turn drive pistons and the result would be the worlds first successful perpetual motion machine.

No, its really more about the temperature and volume of the exhaust gasses than it is "the amount of air the engine moves." Consider a turbo diesel for a moment. Suppose its coasting down a mild hill at 2000 RPM. There's no throttle butterfly on a diesel, so the each cylinder is moving its full volume of air on each cycle, but only an idle flow of fuel. How fast is the turbo spinning? Not very fast at all- no boost generated in fact. Now the truck comes to a hill and the driver puts his foot down to maintain the exact same speed, causing more fuel (but not more air) to flow into the combustion chambers. Exhaust temperature and volume absolutely skyrockets compared to what it was a split second before, and the turbocharger spins up DESPITE THE FACT THAT THE ENGINE IS NOT TURNING ANY FASTER. Once the turbo starts spinning, mass flow further increases because now the cylinders are filling with COMPRESSED air on each stroke, even though the engine is still turning 2000 RPM as the truck pulls hard up the hill.

The same is true with a gasoline turbo engine, with the added feature that the throttle butterfly means that throttle position (not RPM) has an even GREATER impact on gas flow through the turbine than it does in the diesel example.

So you say. Maybe you should try taking some engineering courses instead of "DAGS"-ing all your "knowledge."

Nah. Too easy. Turbo-compounding is the stuff that makes Rube Goldberg smile :-)

Eeyore said in rec.autos.driving:

Sure! When do you want to bring it by?

Yep. Like I said, a turboprop engine with some pistons and a crankshaft thrown in the middle :-p

They also still hold the record for being the most fuel-efficient engines ever to power an airplane, I believe (Wright 3350 turbo-compound radials on the DC-7C). If they don't still hold the record, it was only surpassed in the late 90s or later.

Eeyore said in rec.autos.driving:

If you're a genuine driving enthusiast then front wheel drive isn't for you. My Acura TL (~250 HP) had VERY noticeable torque steer, especially if you launched with your wheels turned (e.g. performing a turn at a traffic light). I shudder to think of what 400 HP would be like in a FWD car...

Apparently Saab engineers never heard of division of labor - the drive wheels drive and the steering wheels steer. FWD is for minivans that need to drive in the snow; it is NOT for high performance cars.

REALLY? Its not at all related to exhaust gas temperature? Better go re-write the physics books.

Or maybe you should "DAGS" on Boyle's Law

:-)

LOL !

Sort of - lol ! Hitting the rev limiter in 2nd because the stereo's on full is slightly embarrasing though. It was good for ~ 70 in my 2 litre Cavaliers though.

How may cars are driveable from pulling away to the legal limit in one gear ?

I used one of them to get from my home to the centre of London in 20 mins once !

Graham

By the book 150 but I have a suspicion it's had an ECU tweak. Maybe 170. Beyond that it needs the intercooler fitted.

I've had loads of FWD cars and maybe I just got used to it. I've never found it an issue. I have however most definitely experienced the power understeer though ! At last it's safe.

Graham

If I lived there, I'd be happy to oblige.

The Aero is totally crazy.

Graham

So how did the 9000 totally thrash its RWD competitors in track racing ?

Graham

And how does the air get into the cylinders? It goes through the throttle plate. It's this plate that determines how much air gets into the cylinders. Open the throttle plate, more air goes in. I'm sorry, but you really don't know as much about this as you think you do.

Even without the throttle, the turbo speed will vary because of varying exhaust temperature (and therefore volume) at a constant engine speed. See my example in my last post regarding a truck going down and then up a hill at constant speed. If you've ever ridden in or driven beside a diesel under those conditions, you can HEAR the turbo change speeds without the diesel changing speeds.

Another easy way to witness this is with goverened engines that run at constant speed. When the load increases, the turbos spool higher even though the crankshaft speed stays constant. I've personally stood beside a Detroit Diesel 12-V-149TI and listened to the 4 turbos spool up and down as the load on the engine varied, but the tachometer never budged.

No. Volume is not conserved.