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Old 12-18-2016, 08:06 PM   #41
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Where would the exhaust gas go, if it wasn't spinning the turbo fan? To atmosphere. The turbo is capturing it, and converting it to mechanical energy by increasing the air charge. Why is that not more efficient?

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HP is needed to drive the turbo, and I'm hard pressed to believe that the output makes it more efficient.
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Old 12-18-2016, 08:16 PM   #42
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The latest Volvo is a four, it has two turbochargers and a supercharger...
I love the sound of my Cummins turbo when I push the throttle, sounds like a D8 Cat getting ready to work.

There is no maintenance on a turbo except to keep the air filter clean and change the oil when you are supposed to.

I had a turbo fail on an Aerostar 601 (it had 4) and the cracked case let exhaust gasses weld the three power cables such that I couldn't close the throttle, select idle cutoff or feather it. 25,000 feet right over the airport and we shut it off because the engine was BTTW and we couldn't descend. Off with the fuel, nearly didn't make it with the unfeathered prop.
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Old 12-18-2016, 08:33 PM   #43
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I've already posted this on another thread today but ......
I rebuilt my 1971 HT6-354 Perkins at 20,000hrs. and rebuilt the turbo at the same time even tho' the turbo didn't need it but what the hell I had the whole damn thing apart anyway. This engine was run at 1600RPM 90% of the time and weighed just a little under 1600lbs. Turbo's in a displacement hull trawler are just fine.
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Old 12-19-2016, 12:16 AM   #44
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turbo or non turbo. more than 70 years turbo diesels manufactured for professional use. I can not understand how someone thought of as old-fashioned way, the turbo diesel is a high risk. or think of an ocean crossing that risk. When using and servicing the machine correctly turbo diesel, turbo serves as certainly as long as the rest of the mechanics of the engine. I would argue diesel unit the most problems than other turbo disintegrate. whether it would be the next step back to the steam engine, they are reliable and simple. Or hot bulb marine diesel and official trawler, these are the great motors from father to son and the grandsons.


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Old 12-19-2016, 12:59 AM   #45
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Where would the exhaust gas go, if it wasn't spinning the turbo fan? To atmosphere. The turbo is capturing it, and converting it to mechanical energy by increasing the air charge. Why is that not more efficient?
Fletcher,

When you throw all that hot air back into the engine, you need to match it with fuel. Air doesn't burn, no free lunch. Plus the HP to just turn the turbo.
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Old 12-19-2016, 03:15 AM   #46
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Fletcher,

When you throw all that hot air back into the engine, you need to match it with fuel. Air doesn't burn, no free lunch. Plus the HP to just turn the turbo.
The hot air then goes through a charge air cooler, gets into the cylinder where the extra oxygen allows more of the injected fuel to burn cleanly, resulting in enough "HP to just turn the turbo", with lots left over for shaft hp.


2016 Buick has a pair of turbos in 2 l, one for low rpms, to get you going, one for higher to keep you going. Lots more power in a small engine. They only got that extra hp by putting turbos on. Also get decent mileage.
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Old 12-19-2016, 06:19 AM   #47
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As you ask for opinion I will give!
About cars first... No turbo,never, ever! The problem with turbo is the rpm. When you are low rpm you don't have any power at all. If you drive a turbocharged car you need to be sure to always be high rpm as if you go low you loose all the power. I am not professional driver at all but sport car lover. I love the flat 6 in my car, it kicks your ass at any rpm, no need for a turbo. Not a general rule but usually turbocharger are used for emission rules and try to compensate underpowered engines.
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As to turbo cars, disagree, my turbo diesel car has heaps of torque and power and response down low. Plenty of (non exotic)performance cars have a diesel option.
As to boats, agree. I`d rather a big slow revving naturally aspirated diesel than a high rpm turbo diesel, it`s just another layer of maintenance and potential for trouble. But, as said above, for new engines, no non turbo option.
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Wifey B: My turbo car has power at all rpm's. 530 hp or so, 0 to 60 in 3 seconds.
I also disagree with Lou_Tribal, sorry Lou. You're out of touch there. I'm still driving a 1990 GT4, and still in awe of it, and I just love the turbo - even the slight lag, as it reminds me not to be a leadfoot and waste fuel when not needed, so it's very frugal of fuel, but when I really want power - wheeee, it's all there. Love it. In a displacement boat - don't miss it, but as has been mentioned, non-turbo unavailable in smaller engines. But really, they are all so very reliable if in a half decent set-up, and with good maintenance. In short, I would never let a turbo put me off, boat or car.
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Old 12-19-2016, 06:19 AM   #48
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The aftercoolers are the maintenance issue with turbos. Not all turbos have aftercoolers but most do.
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Old 12-19-2016, 06:44 AM   #49
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Of course not talking about high end sportcar where a turbo is not there to be able to have a smaller engine but there to increase power output from an already hyper powerful engine. But most of the case, the goal of adding turbo to a car engine is not to get a diabolic engine, it is only to be able to get more from a smaller, lighter engine and increase fuel efficiency.
Can't even agree with you there Lou. In 1983 I bout a Mitsubishi Cordia automatic. Remember them..? I got auto because I was over all the gear changes in the double ratio gearbox of the Mirage that preceded it. Trouble is the 1600cc 4 cylinder in the Cordia was, to say the least, not a rocket. So, I had an expert aftermarket turbo added, and wow..! Suddenly I had 4 cyl 1600cc economy round town, but out on the highway, you could just plant your foot, and drive it like a V8. Found that auto works beautifully with turbo. (Had extra oil coolers added of course, including tranny), but with no coming off boost for gear changes, constant surge - yet even better economy. Loved it - best engine mod I ever made.
Sorry, now back to boat turbos...
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Old 12-19-2016, 06:53 AM   #50
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In 1993 I bout a Mitsubishi Cordia automatic. Remember them..?
Fairly certain this model was not marketed in North America so it is unlikely he would remember them.

Oops just checked Wiki and apparently they were imported. Sorry, I didn't remember it.
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Old 12-19-2016, 07:10 AM   #51
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Not many of us get to decide whether the engine has a turbo or not. We buy what we want, and if it has a turbo, then it has a turbo.

Yep.

When we were shopping for this boat, the choice was pretty much Cummins 450C (what we got), Cummins 480CE (newer models than ours), Volvo 480s, anda very few Cummins 370Bs. "To Turbo or Not To Turbo..." -- that was NOT the question.

So we bought, E Voila! we discover we've got turbos. Non-issue.

The choice was also twins... or twins. And planing hull... or planing hull. Ditto non-issues (although I'd have preferred a single like yours, I think, for lower costs and better ease of access).

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Old 12-19-2016, 07:22 AM   #52
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"When you throw all that hot air back into the engine, you need to match it with fuel. Air doesn't burn, no free lunch. Plus the HP to just turn the turbo."


The same engine with and without a turbo will show a better fuel use per hp produced ratio due to the extra turbulence and air in the cylinders. There is negligible HP required to spin a turbo as that power is being extracted from 'waste'
heat expansion in the exhaust stream. Of course adding fuel will also add hp but the extra air in the cylinders offers higher efficiency at a given level of fuel used.
In diesels this is easier to see as their air/fuel ratio is not fixed and they can run efficiently and very well at ratios of air 4-8X that of gas engines.
I have owned various boats with pairs of diesel engines that are the same except one version had a turbo and intercooler and the other did not.
And we have not yet discussed the marine engines with superchargers and multiple turbo's as of yet....
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Old 12-19-2016, 07:53 AM   #53
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Fletcher,

When you throw all that hot air back into the engine, you need to match it with fuel. Air doesn't burn, no free lunch. Plus the HP to just turn the turbo.
Google "how turbos work", and read Keith's post.
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Old 12-19-2016, 11:22 AM   #54
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Fairly certain this model was not marketed in North America so it is unlikely he would remember them.

Oops just checked Wiki and apparently they were imported. Sorry, I didn't remember it.
And Mitsubishi was one of the first to offer turbos in the US although most of it was initially for Chrysler products.
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Old 12-19-2016, 12:01 PM   #55
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Much tur bo about nothing.
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Old 12-19-2016, 12:13 PM   #56
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Google "how turbos work", and read Keith's post.
Fletcher, Did that, but I understand how turbos work, and there are many variations. Forgive me, but my experience is with aircraft, but the concept is the same.

When you push the air back into the cylinder, it still needs fuel to burn. Like I said there is no free lunch, but they can be more efficient from what I read, but I'm still skeptical that it's worth it. There is also an effort to spin that turbo, but not much and back pressures and other factors come into play.

As far as burning cleaner or more efficiency, the turbo would not necessarily do that. Clean burning and not wasting extra full is just having the correct stoichiometric mixture in the cylinder for burning. Also affecting that is timing. In some cases a variable timing device is used, but I don't know that there's any timing at all in a diesel, suspect it's built into the engine and not adjustable.

And, there is maintenance, and there can be issues. Look at Xsbank's experience with a turbo failure in his plane, that could be deadly. And this can happen in a boat, too. Fortunately, this is rare with good maintenance, but a cracked case could be hard to predict.

It's just one more thing to break.

But, I'll agree, lots of folks like them and a lot are produce.

Doesn't make me want to have them. My first choice is without, but may not have a choice.

Still learning about Marine diesels......
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Old 12-19-2016, 12:15 PM   #57
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Turbo does not really change the efficiency much with regard to the thermodynamic cycle. What it does is allow a smaller engine to make bigger engine power. Smaller engine has less frictional loss from metal things sliding on each other, and has less surface area exposed to the valuable hot gasses. Heat going into relatively cool metal is energy lost.

Turbo engines can be taken to an absurd level like on Yanmar and Volvo up there around 3800rpm. At that speed it takes a good bit of power to shove gasses through little holes. That power comes from the fuel and does not go down the shaft.

On gassers, turbo is complicated. Increase boost and you run into detonation. Reduce compression ratio to avoid detonation, and you kill light load efficiency and low end torque.

Variable geometry turbines really help on the gassers, and also help on diesels. But we have not figured out how to keep marine engine turbos from rotting due to moisture, that would play havoc with the variable geometry hardware.. Would be nice though.

Diesels are easy. Control injection as always, turbo just follows along. You do have to control thermal and mechanical stresses though, or things break. They like to push things right to the limit there, and maybe just a touch over.

Best efficiency comes from a good bit of turbo, but modest engine speed. Most pleasure boat engines top out at 30-35psi gauge pressure. The big freighter engines where efficiency and reliability are God- run like 45psi gauge of boost. That is up there.
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Old 12-19-2016, 12:44 PM   #58
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My only experience with turbocharged engines until I bought Kinship was with a 1994 Mazda RX7. That car had a rotary engine so it dint have a lot of low end torque but really liked to spin up. It had two turbines, the first would kick in at about 2800 rpm and the second ay about 4500. The engines and turbos were great as long as you were meticulous about maintenance and how you drove them. This was the combination of the turbos and the rotary, but they definitely needed a cool down to allow the turbines to cool. At the same time, the engine didn't like to just be started and then stopped, such as moving it in the driveway to wash it. This meant any time the car needed to be moved was an excuse to go out and drive the car hard.

The biggest problem with that 3rd generation RX7 was that the control system for the turbos was using 1990 tech. It was a rats nest of vacuum switches that would determine when the exhaust gas would be gated to first the first then the second sequential turbos. It was the intense maintenance and constant tweaking that finally made me give up the car. However I have never driven anything as fun as that car when you can wind it up. I raced it a lot in autocross. Most of the time I never needed to get out of 2nd gear since course speeds were usually under 70mph. That car had a perfect 50/50 balance. (Sigh)

Now I am driving a 2006 360Z. It has daily driver reliability with its normally aspirated straight 6 and lots of torque. It just isn't quite as much fun as that RX7.

Now my boat has a turbocharged engine. It simple means that I have two additional components to maintain, the turbocharger and aftercooler.
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Old 12-19-2016, 01:20 PM   #59
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Turbo does not really change the efficiency much with regard to the thermodynamic cycle. What it does is allow a smaller engine to make bigger engine power. Smaller engine has less frictional loss from metal things sliding on each other, and has less surface area exposed to the valuable hot gasses. Heat going into relatively cool metal is energy lost.

Turbo engines can be taken to an absurd level like on Yanmar and Volvo up there around 3800rpm. At that speed it takes a good bit of power to shove gasses through little holes. That power comes from the fuel and does not go down the shaft.

On gassers, turbo is complicated. Increase boost and you run into detonation. Reduce compression ratio to avoid detonation, and you kill light load efficiency and low end torque.

Variable geometry turbines really help on the gassers, and also help on diesels. But we have not figured out how to keep marine engine turbos from rotting due to moisture, that would play havoc with the variable geometry hardware.. Would be nice though.

Diesels are easy. Control injection as always, turbo just follows along. You do have to control thermal and mechanical stresses though, or things break. They like to push things right to the limit there, and maybe just a touch over.

Best efficiency comes from a good bit of turbo, but modest engine speed. Most pleasure boat engines top out at 30-35psi gauge pressure. The big freighter engines where efficiency and reliability are God- run like 45psi gauge of boost. That is up there.
Ski,

What is the PSI gauge measuring? Im used to manifold pressure (inHg) on what I've worked on.
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Old 12-19-2016, 01:33 PM   #60
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I just meant "gauge" pressure, psig, in contrast to "absolute" or psia. Psia includes atmospheric pressure, so zero boost is 14.7psia, 0psig. Still just talking manifold pressure same as on aircraft engines. InHg is a common unit for this as a manometer is a really accurate and simple pressure measuring tool.
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