How reliable are turbo engines?

"223rem" said in rec.autos.driving:

OBTW, the typical diesel-electric railroad locomotive is turbocharged, and these babies can run over a MILLION miles between major overhauls. Of course, these are well-designed engines that aren't abused by aggressive and/or incompetent drivers. :)

Like any other component they eventually wear out. If you drive the car hard and don't let the turbo spin down before shutting the engine off then I would expect a shorter life. If you stretch oil changes you will also contribute to an early demise. That said, if you give the car frequent oil changes, keep up with other maintenance and don't drive it hard there is no reason you should not get 300,000 miles from the engine and all components including the turbo.

You haven't ridden Amtrak recently, have you?

--scott

The bearings in a turbocharger are fed oil in sufficient quantities to both lube and cool them; that's not a problem, as has been shown by the number of turbos being used without a problem from their bearings. There can be a problem, though, if proper procedures aren't followed. A cool-down period is needed if the engine has been run hard; usually, this means a 5-10 minute idle before engine shutdown. If this isn't done, oil in the turbo can "coke" (solidify from overheating), plugging the oil lines. Also, a high-quality oil must be used; often, this means a synthetic is best. The oil requirements are spelled out in the owner's manual, and again on a sticker in the engine compartment.

Following the thread, when was the last time a turbocharged diesel engine in a diesel electric locomotive failed. I'm not aware of any.

snipped-for-privacy@panix.com (Scott Dorsey) said in rec.autos.driving:

Actually, it was an Amtrak locomotive running on the Pacific Surfliner route where I saw the "engine computer" display had logged 900,000+ miles since (IIRC) 1998.

Turbocharged engines are typically *LOWER* revving engines than non-turbos. With a non-turbo, you have to rev the snot out of it (or make it larger displacement) to move the same amount of air/fuel that a same-sized turbo engine can move. Compare a non-turbo Honda VTEC (8000 RPM) to a turbo engine of the same output (typically 6000 RPM or less).

Turbos can be extremely reliable and don't really need any more maintenance than others except

1) use high-quality oil (preferably synthetic) 2) Never and I mean NEVER shut it down immediately after running it hard.

The turbo 4-cylinder was really brought into the mainstream way back in the 80s when Chrysler was putting 2.2 and 2.5 Turbo I and Turbo II engines in everything from New Yorkers to Daytonas. Those engines were very tough and reliable- something that gets forgotten now that most of the ones you see still running are 20-year-old hand-me-downs. Another superb turbo implementaion from that era was the Buick 3800 turbo. Great machines. The fact that those engines were replaced by non-turbos and that the remaining turbocharged Mitsubishes, Saabs and Volvos of the 90s were such piles of cr*p is what has sullied reputation of the turbo engine IMO, but it was the implementation, not the turbo itself.

Jet engines have the same type of moving parts as a turbocharger. They require FAR less maintenance than piston airplane engines. You do the math :-)

Seriously, the turbo is just a shaft with a bearing in the middle. As long as that bearing gets oil (its pressure fed from the engine itself) and isn't cooked by shutting down the engine after running hard so the turbine wheel is glowing red hot, it will last forever.

Floyd Rogers wrote:

The turbo increases manifold pressure as soon as it can to get the vehicle accelerating as desired. If we wait until high revs to get the boost, what good is that? Don't need it by that time. The pop-off valve (relief valve) is to limit the boost pressure at any RPM, not just high RPM. It will tend to pop at higher RPM because that's where more power, and more exhaust to drive the turbo, is generated. High boost pressures result in very high combustion pressures, with accelerated engine wear and possible catastrophic failure. At the least, detonation or preignition become serious issues. Turbos and superchargers can be used to get more power out of a given size of engine, or it can be used simply to improve the volumetric efficiency of the engine. The cylinder of a normally-aspirated engine never sees atmospheric pressure at the bottom of the intake stroke because of the drag of the induction system and the short time available for intake air to get into the cylinder, so it never gets all the air and fuel it could. Many aircraft are "turbo-normalized," turbocharged to no more than sea-level pressure to get the cylinder air/fuel volume up, and therefore HP it was designed to produce without stressing it, and to counter the drop in air pressure (and density) as the airplane climbs. The engine lasts longer than a similar engine that is boosted beyond the 30" Hg point. Most aircraft turbos are waste-gate controlled, where the exhaust passes either through the trubo or through a bypass pipe that has a throttle-style rotating plate in it. Rotate the plate closed, cutting off the escape path, and the turbo spins up. There are various manual and automatic waste-gate controls. I haven't heard of a similar control in an auto. I suppose the relief valve is simpler.

Dan

I wasn't doubting that they could run such long hours, I was just doubting that they weren't abused by aggressive and incompetent drivers.

--scott

Here's mine. I showed my father (who is a classic V8 guy) and he said he wished his engines held up like that at high RPM :)

So that you can have extra power at low RPM. In fact, some cars have sequential twin turbo: a small turbo that peaks at low RPM, and a larger turbo that peaks at higher RPM. The small turbo addresses the issue of the car running like crap until there is sufficient RPM to drive the larger turbo.

They don't. Usually, boost is limited by a wastegate (which I'll describe later on in this post).

I'm not familiar with pop-off valves, but this page:

that the reason they're used in Champ Car is toensure that all cars in the field have the same maximumboost level.

Also, pop-off valves are not to be confused with blow-off valves (aka. intake relief valve) , which I'll also describe later.

The reasons for limiting boost are: 1) The turbo will break if you let the turbine spin faster than its specification. 2) The engine will break if you put too much power through it.

If you have a big turbo on a small engine, that isn't properly limited, you will end up exploding a piston or bending or breaking the con-rods and crankshaft.

Cars with turbochargers often have higher-spec pistons and internals than other cars. If you are adding a turbo to an engine that was not designed for it -- or if you are upgrading the turbo on an existing engine -- then getting tougher pistons is usually a requirement. High-performance parts suppliers usually have kits of pistons, rods & cranks for upgraded power applications.

Back to the wastegate topic now:

Most of the time, the turbocharger has an internal wastegate that keeps it from going too fast. This can either be actuated mechanically, or electronically. In the latter case, sometimes control is given to the drive to select the maximum level of boost (this is called an electronic boost controller).

In higher end applications, the wastegate is external; this means that better technology can be used in the wastegate.

If you fit an external wastegate to a car that already has a turbo with internal wastegate, you fix the internal one shut (by welding, if necessary).

Finally, the intake relief valve (the psssht you hear on most turbo cars when they change gear) is for a different reason entirely. When the throttle plate closes, what happens to all the compressed air that was just about to be forced through it? The blowoff valve detects when manifold pressure reverses, and opens to let this excess gas be vented to the atmosphere. (Other systems re-route this gas back to an earlier point in the intake system, but this doesn't sound as cool).

Without such a valve, the compressed air has no choice but to flow backwards through the turbo and out of the intake filter, when the throttle closes. This is undesirable because it can cause damage to the turbine.

For sure.

Renewed might perhaps be a better word.

Graham

What's wrong with a 90s Saab ?

Graham

The turbo usually has sleeve bearings, while the jet has ball and/or roller bearings. The jet engine also has some rather complex cooling arrangments in the hot section that I haven't seen in a turbo, but of course the jet's hot section gets somewhat hotter than the turbo's. You are right about the jet's life and reliability. The lack of reciprocating forces and constantly changing pressures has a lot to do with that.

Dan

snipped-for-privacy@panix.com (Scott Dorsey) said in rec.autos.driving:

LOL!!!

Eeyore said in rec.autos.driving:

Shall I count the ways?

1) They're fugly. 2) They're expensive relative to what you get (low bang/buck ratio) 3) They're fugly. 4) They have ugly, uncomfortable interiors. 4) They're fugly. 5) Did I mention they're really not very attractive to look at? :)

I like my 9000. I think it looks pretty classic. You also don't get many 'executive' hatchbacks either.

I'd also say they have some of the best seats that exist in any car.

They're a bargain on the UK second-hand market too.

Graham

Eeyore said in rec.autos.driving:

LOL!! I had a sneaking suspicion you did...

I confess I haven't actually sat in a Saab since the 70s (I dated a Swedish girl in high school who had one). Back then the seats were cheap and hard - very uncomfortable.

I believe the reasons for that are listed above. :)