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Old 04-15-2017, 02:33 PM   #21
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Interesting idea. I also am not sure how much the turbine spins up at the rpms we run. Without the turnbine compressing the air and raising the temps, the aftercooler may be unnecessary. OTOH, since we do operate in 50 degree water most of the time, it is likely cooling the intake air on those rare hot days giving us a bit more power.

I wonder what would happen if the aftercooler were removed? Install an EGT gauge and keep a close eye on it?
You can easily add a boost gauge to most engines. Often there is a tapped 1/4 20 pitch hole in the manifold for a gauge.

Since you're not cooling it back off and making it more dense, the Delta T won't be as high, so you won't get as much power from each cylinder. The amount of power an engine generates is dependent on the amount of temperature / pressure rise in each cylinder. Starting with cool air before ignition will result in higher compression and horsepower.

Will you be able to tell the difference? Maybe?

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Old 04-15-2017, 02:41 PM   #22
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"You can easily add a boost gauge to most engines. Often there is a tapped 1/4 20 pitch hole in the manifold for a gauge."


This is a great idea that will tell you how your engine is running in real time - add an EGT gage at the same time and you have some valuable data. This combo has been added to many of the Cummins 6b's and offers a very good way to know if you are inadvertently pushing the engine to hard at any particular rpm - they will also tend to show if you have fouling going on.
Diesel engines burn more efficiently with extra air and higher turbulence - removing the intercooler with drop the air concentration and lessen the flow/turbulence.
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Old 04-15-2017, 03:05 PM   #23
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The reality is it's going to be determined by what generation engine you're dealing with. Today's engines are going to be common rail and turbocharged and they've now been that way for a long enough time that, properly maintained and serviced, they'll have great longevity. I've never had a diesel that wasn't common rail and wasn't turbocharged and I've had no issues.
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Old 04-15-2017, 03:11 PM   #24
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I don't have turbos on my current boat's engines, but I have had a few turbocharged motors in my lifetime, I would not point at the turbo specifically for increased maintenance or reduced longevity on any of them. That being said.. if you're talking philosophically about a boat... weight and space improvements for the engine probably don't have the same benefits as aircraft (earliest application) or automobiles (most applications).
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Old 04-15-2017, 04:49 PM   #25
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This got me wondering about how much the boosted air heats up, so I just checked. We are running at about 55% load, and boost pressure is 9.5 psi. The engine is one level below continuous duty, and can run full power for 16/24hrs, and at 100 Rpm below full power for the remaining 8hrs, then repeat continuously.

Intake air is 65f, and pipe carrying the boosted air is 180f. EGT is 710F with a max of 780f or something very close to that.

So that will put some numbers around the theory.
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Old 04-16-2017, 01:50 PM   #26
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Hi,

I stumbled onto the Trawler Forums while looking for information on Becker rudders, and started reading this thread as I have considered de-turboing my main engine. I finally registered in the hope of dispelling a couple of common myths about turbocharges.

#1 - Turbodiesels are inherently less fuel efficient: They're not, as evidenced by commonly available data. As for why, a common (and partially correct) assumption is that the smaller engine size for a given power level leads to reduced mechanical losses. There is a different and more important explanation, tough: A significant portion of the mechanical energy generated by the piston is lost to pumping air through the engine. Because a centrifugal impeller compressor is much more efficient than a piston pump at these low delta-p numbers, adding a turbo to any given diesel engine (and dropping compression by a point or two) tends to yield a fuel efficiency increase around 2-3% for a given power level.

2 - Turbocharging an engine leads to increased EGTs: Anyone who has lost a turbo on a non-compensated engine knows how wrong that is (EGTs instantly go through the roof). In fact, just adding a turbo to an engine (as above) will lead to higher lambda, which leads directly to lower EGT. That being said, turbocharged engines are generally able to sustain higher EGTs by maintaining combustion efficiency at higher power densities, as well as having marginally better piston cooling for a given EGT, which is why turbodiesels tend to run hotter exhaust.

3 - Turbodiesels wear out quicker: Again, empirical evidence suggests otherwise. Take my main engine as an example; It's a FIAT 8281 17 liter V8 @ 500-ish hp. The same engine delivers 310 bhp @ 1700 rpm NA (16:1 compression, injection fixed at 18 degrees btdc). The continuous duty turbo version (no intercooler) delivers 370 bhp @ 1800 rpm, with 15:1 compression and injection start 26 degrees btdc. The latter configuration has a typical TBO of 25k hours, and I know of one concrete example that ran almost 50k hours on a set of rings (although that was pushing it). That's quite a bit, no? Furthermore, a lot of medium speed marine engines have scheduled liner replacement at 50k hours, and they're all turbocharged these days.

That being said, the turbocharger itself has a much shorter life span than the engine, and you'd be lucky to get 10k hours out of one. Short cycling without pre-heating and pre-lubrication drastically reduces that number, and I've seen plenty of pleasure use turbos die "natural" deaths before they reach 1.500 hours. I actually murdered my own turbos even sooner than that, by a lot of really short run cycles (<1hr), hence the interest in de-turboing despite the expected drop in fuel economy.
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Old 04-16-2017, 02:05 PM   #27
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Henning:

Unless you change your injection pump after removing a turbo from an engine designed for a turbo, won't it pump too much fuel for the reduced air available at higher rpms?

Also, not to quibble (too much), I find it hard to believe that a centrifugal compressor is more effiicient at compressing air than a simple piston, when that piston has to go up and down anyway, ie almost all parasitic losses are there anyway.

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Old 04-16-2017, 02:25 PM   #28
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This got me wondering about how much the boosted air heats up, so I just checked. We are running at about 55% load, and boost pressure is 9.5 psi. The engine is one level below continuous duty, and can run full power for 16/24hrs, and at 100 Rpm below full power for the remaining 8hrs, then repeat continuously.

Intake air is 65f, and pipe carrying the boosted air is 180f. EGT is 710F with a max of 780f or something very close to that.

So that will put some numbers around the theory.
Some random Easter Day thoughts. --

In my case the engines normally run at 3o - 35% rated load with boost around 7 psi (waste gate controlled), intake air through the ER 70 to 100F, EGT at 500F and boosted air (with IR gun) 140 to 150F dependent upon the cylinder.

Yes, the engines are under loaded but designed for task as their real intention is gensets or small equipment. I wish the marinization side were as trouble free as the turbos. But as previously noted for newer builds, turbo diesels are emissions built for today's world.

Turbochargers are well proven and have been used to great success on all manners of hard working diesels for well over half a century. It would seem that lightly loaded boat engines where fuel consumption and BSFC is not a concern turbos are not a necessity. But again, emissions' requirements have changed that too with turbo free new build diesels now a rarity once above 100 HP.
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Old 04-16-2017, 02:27 PM   #29
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Turbos, do one thing. They wear out engines prematurely, period. When you force air, either thru, the intake or the exhaust, you lower the engine life. 671 Detroits naturals, will run forever, put boost, rebuilds, at 2500 hours. Does not matter what anybody says, any boost, causes early rebuilds, just ask, people who do this for a living, not opinions, from laymen, just COMMON SENSE, from engine rebuilders..
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Old 04-16-2017, 02:34 PM   #30
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Henning:

Unless you change your injection pump after removing a turbo from an engine designed for a turbo, won't it pump too much fuel for the reduced air available at higher rpms?
That depends. A compensated pump you don't really have to touch, and for an uncompensated one you could just turn the rack limiter screw. You might wanna change the pump cam anyway, though, to maintain sensible injection durations, but then you also need to consider the injectors, and... I'm still undecided, and would probably only change the timing if I do it on my own engine.

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Also, not to quibble (too much), I find it hard to believe that a centrifugal compressor is more effiicient at compressing air than a simple piston, when that piston has to go up and down anyway, ie almost all parasitic losses are there anyway.
Compression heat lost to the combustion chamber walls account for quite a bit of it, and the flow losses in the intake and exhaust tracts are also considerable. Look at a typical PV diagram, and you'll notice that the area inside the lower loop (which represents the portion of the pumping loss related to flow resistance) is quite large when compared to the upper loop (the compression and power strokes). Mechanical friction losses hardly factor into the equation. Depending on which source you believe, thermodynamic and flow related pumping losses are 3-4x the mechanical resistance of the whole engine (which incidentally is mostly piston ring drag and a bit of valve train friction, but I digress).

(Note that the images are just something google spewed up when queried about "PV diagram", and represent idealized theory rather than measured values, which tend to be rather less ideal.)
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Old 04-16-2017, 02:37 PM   #31
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Turbos, do one thing. They wear out engines prematurely, period.
(...)
just ask, people who do this for a living, not opinions, from laymen, just COMMON SENSE, from engine rebuilders..
I actually do this for a living, but anyway... the example you give of premature wear in jimmies is related to higher power densities, not the mere presence of a turbocharger.
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Old 04-16-2017, 02:45 PM   #32
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Hi,

I stumbled onto the Trawler Forums while looking for information on Becker rudders, and started reading this thread as I have considered de-turboing my main engine. I finally registered in the hope of dispelling a couple of common myths about turbocharges.

#1 - Turbodiesels are inherently less fuel efficient: They're not, as evidenced by commonly available data. As for why, a common (and partially correct) assumption is that the smaller engine size for a given power level leads to reduced mechanical losses. There is a different and more important explanation, tough: A significant portion of the mechanical energy generated by the piston is lost to pumping air through the engine. Because a centrifugal impeller compressor is much more efficient than a piston pump at these low delta-p numbers, adding a turbo to any given diesel engine (and dropping compression by a point or two) tends to yield a fuel efficiency increase around 2-3% for a given power level.

2 - Turbocharging an engine leads to increased EGTs: Anyone who has lost a turbo on a non-compensated engine knows how wrong that is (EGTs instantly go through the roof). In fact, just adding a turbo to an engine (as above) will lead to higher lambda, which leads directly to lower EGT. That being said, turbocharged engines are generally able to sustain higher EGTs by maintaining combustion efficiency at higher power densities, as well as having marginally better piston cooling for a given EGT, which is why turbodiesels tend to run hotter exhaust.

3 - Turbodiesels wear out quicker: Again, empirical evidence suggests otherwise. Take my main engine as an example; It's a FIAT 8281 17 liter V8 @ 500-ish hp. The same engine delivers 310 bhp @ 1700 rpm NA (16:1 compression, injection fixed at 18 degrees btdc). The continuous duty turbo version (no intercooler) delivers 370 bhp @ 1800 rpm, with 15:1 compression and injection start 26 degrees btdc. The latter configuration has a typical TBO of 25k hours, and I know of one concrete example that ran almost 50k hours on a set of rings (although that was pushing it). That's quite a bit, no? Furthermore, a lot of medium speed marine engines have scheduled liner replacement at 50k hours, and they're all turbocharged these days.

That being said, the turbocharger itself has a much shorter life span than the engine, and you'd be lucky to get 10k hours out of one. Short cycling without pre-heating and pre-lubrication drastically reduces that number, and I've seen plenty of pleasure use turbos die "natural" deaths before they reach 1.500 hours. I actually murdered my own turbos even sooner than that, by a lot of really short run cycles (<1hr), hence the interest in de-turboing despite the expected drop in fuel economy.
I'm sure the diesel engine builders would have an opposing comment or two. Having been involved with Cat dyno testing on many diesels, my experience is very different than you have noted.

The last before I retired was with 4000 HP engines operating at 15.000 feet. Fuel efficiencies and HP obtained matched performance at sea level. This would not have been possible without 21st century engineering including computer controls and very interesting quad turbo intake design. Cooling at these altitudes is a huge challenge.

Last but not least, I've seen turbos easily go 15,000 hours or more in off the road commercial operation. Dozens of them. Never a concern except when lubrication is lost due to fitting or hose issues.
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Old 04-16-2017, 02:47 PM   #33
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I actually do this for a living, but anyway... the example you give of premature wear in jimmies is related to higher power densities, not the mere presence of a turbocharger.
I did this for a living also. The reason manufacturers, put boost was to increase power, and hence, more fuel, by bigger injectors, that is why it was done, which increased Temps, compression heat, etc, which shortened life.
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Old 04-16-2017, 03:14 PM   #34
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Dont all the 71 series have blowers?
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Old 04-16-2017, 03:21 PM   #35
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Dont all the 71 series have blowers?
Sir, 671 naturals, will run and run. The power density, is only achieved, by more fuel, from blowers added, or they will run too lean, hence bigger injectors. And hence , wears pistons, rods, crank, etc.
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Old 04-16-2017, 03:24 PM   #36
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Last but not least, I've seen turbos easily go 15,000 hours or more in off the road commercial operation. Dozens of them. Never a concern except when lubrication is lost due to fitting or hose issues.
Fair point; There are bunches of factors affecting turbo longevity, and larger turbos do live longer - my experience is far from all-encompassing there. I do stand by my statement that the life of the turbo itself is the limiting factor with turbocharged diesel engines, though.

As for the rest, I don't really understand your objection to my argument. Your experience with normalizing large Cats relates to it how? And how does your experience differ from what I say? I'm sincerely curious.
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Old 04-16-2017, 03:29 PM   #37
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Dont all the 71 series have blowers?
Indeed they do, as do the 92s (and I believe the 53s and 149s) but not the 51s. However, blower displacement is closely matched to scavenging air demand, so there isn't really much over pressure being made. The blower is there to ensure somewhat acceptable scavenging when the engine is operating off its ideal speed range.

When the engines are turbo charged, the turbo is added in-line with the blower.
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Old 04-16-2017, 05:39 PM   #38
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Indeed they do, as do the 92s (and I believe the 53s and 149s) but not the 51s. However, blower displacement is closely matched to scavenging air demand, so there isn't really much over pressure being made. The blower is there to ensure somewhat acceptable scavenging when the engine is operating off its ideal speed range.

When the engines are turbo charged, the turbo is added in-line with the blower.
So a blower and a turbo charger are different things? I assumed blower was slang for a turbo charger.
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Old 04-16-2017, 05:50 PM   #39
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So a blower and a turbo charger are different things? I assumed blower was slang for a turbo charger.


No, a blower is either belt or gear driven pump that pressurizes the incoming air for the engine.


A turbo is powered by the exhaust to pressurize the incoming air.

A blower does not have turbo lag, but spins at engine rpm speeds. A turbo spins up only after you throttle down, and the exhaust spins the turbine, spinning the pressure side faster, and increasing air flow and pressure.
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Old 04-16-2017, 07:26 PM   #40
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No, a blower is either belt or gear driven pump that pressurizes the incoming air for the engine.


A turbo is powered by the exhaust to pressurize the incoming air.

A blower does not have turbo lag, but spins at engine rpm speeds. A turbo spins up only after you throttle down, and the exhaust spins the turbine, spinning the pressure side faster, and increasing air flow and pressure.
Are you talking about a supercharger?
And engines fitted with both supercharger and turbocharger?
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