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Old 08-07-2020, 09:23 PM   #1
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Perkins 135 hp

Does anyone know what the continuous operation rpm is for a 135 hp Perkins is..non turbo tw suffix on serial number. Thanks, cliff
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Old 08-07-2020, 10:57 PM   #2
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Hey Cliff,

I think the TW is a 6.354.4 "Series 4" engine.

By memory, it makes that 130hp at 2800rpm with a continuous rating of 2400rpms.

Some boats are geared and propped to push the rpms down to reduce noise. People figured they were going slow anyway and didn't care about the loading. My old boat was this way until I got a hold of it.

If you can't get it to 2800rpm wide open throttle (WOT) under load. I'd keep continuous to 85% or less of what you can get.

...but I am just guessing about your engine.

There is a tag on the injector pump. Can you post a picture? The numbers tell the configuration.
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Old 08-07-2020, 11:54 PM   #3
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Great reliable engine and as gkesden says 2800 flat out and 2400 cruising.
Your speed is dependant on your boat hull shape.
I differ from gkesden in that I have a semi displacement boat and run it at displacement speed for economy and low noise levels.
I've deliberately 'over propped' my boat to give hull speed at peak torque curve on the engine with least vibration/engine noise.
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Old 08-08-2020, 12:55 AM   #4
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I guess I'll add that, to a point, overloading a naturally aspirated engine isn't really a bad thing to do -- it just trades lower noise and vibration at intended cruise speed for a lower maximum output, which one never intends to use. This is apparently the trade the former owner of my old boat and Irish Rambler made.

But, beyond a certain point, it runs into problems. At the lower RPMs the engine can't get enough air to burn all of the fuel that the throttle is calling for, as the air is exchanged with each cycle. So, it starts to run dirty -- grey to black smoke. And, that isn't food for the engine.

But, my old boat was a 6.354MGT, an older 185hp turbo version of the engine. And this introduced another problem (which you don't have). Overloading it to get the RPMs down -- meant the turbos never got to spin up. And, that was bad for them. They just choked and sooted up.

I also didn't care for having a 6.5kn idle speed at 750rpm, which was the sort of crazy extreme to which it had been taken. (But, it sure ran quiet!)
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Old 08-08-2020, 08:05 AM   #5
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Just to clarify, one of the factors that must be taken into consideration is the type of injector pump fitted to the engine. Most marine engines have an all speed governor which regulates the throttle opening though all the engines speed range others mounted from trucks have a two stage governor and these operate under throttle and load, ie if the throttle opening is at 900 and a load comes on the motor it will automatically rev more to compensate and vice versa with a light load will reduce the throttle opening.
However we'll stick to basics here and assume that we are using an all speed governor.
We run ours at optimum peak torque/revs and so its not overloaded and we don't get black smoke. We may get a slight hint of smoke if we open the throttle very quickly.
Turbo engines have different requirements and some people talk about a turbo 'kicking in', that's nonsense because it runs all the time. Simply the effect is more noticeable above certain revs.
A high speed turbo engine running at constantly low revs will certainly begin to soot up the turbine blades after some time and needs to be given a blast at a higher speed = higher exhaust temperature to burn off the soot from the turbine blades, this usually clears after 5 or 10 minutes and they run clean again.
A point to note with a turbo engine is that for a longer life and less problems that after a high speed run it must be allowed to idle for about 5/8 minutes to allow even dissipation of heat around the head to relieve thermal stresses.
This is an important point for cars and trucks also

Often people believe the misconception that a turbo engine is a high speed engine which is false as some boat engines only rev at 250-300 rpm and are turbo'd, it all depend on the engineering requirements.
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Old 08-08-2020, 09:36 AM   #6
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I'd like to react to some of what Irish Rambler offered, because I think that there are some very important considerations with turbo engines, generally, and in the 6.354, in particular, that should be considered before significantly over-propping a turbo engine.

And, I do think that it makes sense to consider the point where the boost provided by the turbo exceeds the parasitic loss it imposes as the point where a "turbo kicks in".

But, I think that we are getting way into thread drift space -- especially for a thread about the RPM specs of a naturally aspirated version of the engine! So, if and when anyone cares, they can hit me up or start a new thread. (And, I think most of it has already been said in many threads by others...so probably no need...)
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Old 08-08-2020, 10:14 AM   #7
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Here are a couple of pictures. Between the 2 pictures you should be able to make out the whole number. Thanks very much for your advice.
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Old 08-08-2020, 10:37 AM   #8
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Okay. That is a pretty standard pump for the 6.3544.

If you take a look at that last line, it shows pump settings. The last one is the "Wide Open Throttle (WOT) -- *NO* load" setting: 3190.

In other words, if you'd leave the boat in neutral, let it fully warm up, and push the throttle lever on the pump full-open, that is the RPM that you'd expect to develop. Test at home at your own risk :-)

In terms of a general algorithm, the WOT-load RPM is about 10% below this. Rough numbers, 2871 RPM. So, this is fully consistent with my memory that the publsihed nominal full-load WOT RPM is 2800 for your engine.

Remember that this number is a nominal number for a nominal boat in a nominal configuration, etc, etc, etc. It wouldn't be unusualy to see a boat in the real world clock in at 100 or 200 RPMs below this, even if folks weren't intentionally trying to make the engines run slower to get less noise and vibration.

Also, in order to ensure that the throttle controls don't get slammed ofrward and over-rotate the throttle lever on the pump, most installers set the controls so that they cannot actually move forward far enough to get the engines to full throttle. I've had a few installers tell me they try to set it back by about 100rpm. I guess that is a common heuristic for "usually enough rotational margin to make sure that, as things age a paniced driver can't slam it forward and break things."
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Old 08-08-2020, 11:10 AM   #9
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Thank you very much. Cliff
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