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Old 06-24-2020, 10:27 AM   #1
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Turbo boost pressure

I recently installed a turbo boost gauge on my JD4045TFM50. The turbo boost kicks in at about 1700rpm and is 11psi at WOT of 2400rpm. I´ve been unable to find any specs on what sort of pressure I should expect from the turbo boost. I´m trying to get a sanity check if these figures seems reasonable for this engine. Thanks
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Old 06-24-2020, 10:43 AM   #2
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What does the owners manual or repair manual say?
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Old 06-24-2020, 11:07 AM   #3
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What does the owners manual or repair manual say?
It says nada, hence my question. Turbo gauge is not standard and the specs provide no info.
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Old 06-24-2020, 11:18 AM   #4
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I think this is what you are looking for.


Intake manifold pressure is listed as 18 psi.
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File Type: pdf 101kW-2500rpm.pdf (32.5 KB, 27 views)
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Old 06-24-2020, 12:31 PM   #5
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I think this is what you are looking for.


Intake manifold pressure is listed as 18 psi.
Thanks, much appreciated, this is exactly what I was looking for. I had the engine specs I got from boat diesel.com but for whatever reason this didn't include manifold pressure.

I regularly clean the air filter so am surprised I was only able to achieve 11psi if its rated for 18psi. I'll replace the air filter to see if this increases the boost any. Anything else which would prevent a too low pressure boost?

Engine appears to be running good and its a new turbo gauge so I believe the 11psi is accurate.
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Old 06-24-2020, 12:52 PM   #6
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If you're only seeing 11 PSI at WOT and also reaching expected RPM, you might just not be propped to get the engine to 100% load.
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Old 06-24-2020, 01:01 PM   #7
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If you're only seeing 11 PSI at WOT and also reaching expected RPM, you might just not be propped to get the engine to 100% load.
That might be true. But if you do reach rated wot rpms and you are happy with the engine's performance you can just leave it under propped and the engine will be happier than it would be by increasing pitch to get the maximum hp out of the engine.

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Old 06-24-2020, 01:11 PM   #8
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That might be true. But if you do reach rated wot rpms and you are happy with the engine's performance you can just leave it under propped and the engine will be happier than it would be by increasing pitch to get the maximum hp out of the engine.

David
David, ok thanks for clarifying this point. This particular engine is rated at 120HP, so if its rated for 18psi manifold pressure am I correct to assume at 11psi its only producing 11/18 * 120HP = 73HP or there abouts at WOT?

I'm not sure why I would want to increase the prop pitch, with the prop on now I can achieve hull speed at about 1800rpm. Would an increased prop pitch give more pulling power, such as for towing?
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Old 06-24-2020, 01:30 PM   #9
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David, ok thanks for clarifying this point. This particular engine is rated at 120HP, so if its rated for 18psi manifold pressure am I correct to assume at 11psi its only producing 11/18 * 120HP = 73HP or there abouts at WOT?
In NA form the 4045-50 is rated at 84hp. If, and a big if, turbo boost is directly related to HP your 11/18 multiplier would yield about 110hp. If you're achieving full rated RPM you should be OK.

Assuming so equipped, when was last time you had the after cooler off for cleaning or at least checked with a bore scope?
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Old 06-24-2020, 03:08 PM   #10
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David, ok thanks for clarifying this point. This particular engine is rated at 120HP, so if its rated for 18psi manifold pressure am I correct to assume at 11psi its only producing 11/18 * 120HP = 73HP or there abouts at WOT?

I'm not sure why I would want to increase the prop pitch, with the prop on now I can achieve hull speed at about 1800rpm. Would an increased prop pitch give more pulling power, such as for towing?
First question- no. To use the rough thermodynamics you are trying to apply here (and they are very rough and don't take all factors into consideration), all pressures need to be in absolute values, so add 14.5 to each number. Then the very approximate hp would be 25.5/32.5 * 120HP = 94.

Second question- probably not, but depends on the speed and engine rpms. Tugs use a flatter pitch prop for more pulling power at low speed than would be required to fully load the engine at wot.

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Old 06-24-2020, 03:41 PM   #11
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That 18psi is for a 135hp at 2500. A 120hp at 2400 will be somewhat different. Need the spec sheets for your engine.
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Old 06-24-2020, 03:48 PM   #12
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n EGT gauge, exhaust gas temperature, would be more useful. Getting 18 psi or whatever boost, isn't doing the engine any good if you're eating the piston tops, or rings, valves or cylinders.
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Old 06-24-2020, 03:59 PM   #13
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David, ok thanks for clarifying this point. This particular engine is rated at 120HP, so if its rated for 18psi manifold pressure am I correct to assume at 11psi its only producing 11/18 * 120HP = 73HP or there abouts at WOT?

I'm not sure why I would want to increase the prop pitch, with the prop on now I can achieve hull speed at about 1800rpm. Would an increased prop pitch give more pulling power, such as for towing?
I think your math is flawed as it would dictate that a non-turbo engine would produce zero horsepower. If atmospheric pressure is about 14psi, a more reasonable equation would be (14+11)/(14+18) * 120 hp = 94 hp.
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Old 06-24-2020, 04:06 PM   #14
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n EGT gauge, exhaust gas temperature, would be more useful. Getting 18 psi or whatever boost, isn't doing the engine any good if you're eating the piston tops, or rings, valves or cylinders.
Thanks, yes I recently installed an EGT also. Temps at WOT all seem to be within range.
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Old 06-24-2020, 04:09 PM   #15
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That 18psi is for a 135hp at 2500. A 120hp at 2400 will be somewhat different. Need the spec sheets for your engine.
The top of that spec page shows a M2 and M3 engine and my engine is a M2. If there was a difference on manifold pressure between the M2 and M3 wouldn’t the spec sheet show this?
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Old 06-24-2020, 04:18 PM   #16
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In NA form the 4045-50 is rated at 84hp. If, and a big if, turbo boost is directly related to HP your 11/18 multiplier would yield about 110hp. If you're achieving full rated RPM you should be OK.

Assuming so equipped, when was last time you had the after cooler off for cleaning or at least checked with a bore scope?
Thanks, as far as I know the TFM doesn’t have an after cooler. On another thread I thought it said the SFM version that has an aftercooler. I asked a question on the Krogen owners forum on turbo maintenance and the consensus response was that the TFM turbo didn’t require any periodic maintenance and barring a mechanical failure should last until rebuild time.

I did read on another article suggesting to lightly mist soapy water into the turbo while running. The JD manual is silent on any periodic maintenance. If you have anything to share on this please do share.
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Old 06-25-2020, 05:56 AM   #17
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The top of that spec page shows a M2 and M3 engine and my engine is a M2. If there was a difference on manifold pressure between the M2 and M3 wouldn’t the spec sheet show this?


I think Ski is right. I suspect the data sheet lists max manifold pressure, and that would be for the highest rate output version of the engine. Yours will be lower, but they don’t say how much. My estimate, using highly proprietary and top secret formulas, is about 11 psi.
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Old 06-25-2020, 07:16 AM   #18
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The truck diesel performance crowd uses a general "rule of thumb" of 10 hp per 1 pound of boost. I know that's not scientific but in my very limited experience it has been in the ballpark.
Using that "theory" you are putting out about 110 hp.
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Old 06-25-2020, 08:35 AM   #19
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You can't use a ratio of 11psi to 18psi. Have to use absolute pressure. Have to add 14.7psi to each. So if you want to play with ratios it is 25.7 to 32.7.

Engines without aftercoolers usually run lower boost than ones with AC's.

If engine is not making black smoke at full power, manifold pressure is "good enough". Usually.
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Old 06-25-2020, 09:14 AM   #20
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I think Ski is right. I suspect the data sheet lists max manifold pressure, and that would be for the highest rate output version of the engine. Yours will be lower, but they don’t say how much. My estimate, using highly proprietary and top secret formulas, is about 11 psi.
That would make sense as the only difference between the M2 and M3 is an additional 100rpm WOT.

So if I understand correctly the only difference between the M1 to M4 engines is the higher rpm which coincides with a higher boost pressure to squeeze more hp out of the same displacement. As you squeeze more hp out of the same displacement the continuous duty cycle declines due to higher heat levels. Is this right?
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