Df140 rpm

[Fluker4]

I'm new to these four strokes
What is a safe rpm to cruise at or should I say without hurting the engine

[ChrigelKarrer]

Cruising speed is usually considered on a outboard somewhere between 3500 and 4500 rpm with a preference to 3500-4000rpm.
This may vary depending on your hull and propeller, if you need higer rpm then 4500 to keep planing speed then you have probably either the wrong prop or a too less HP for your boat.
Chris

[Fluker4]

I've always had a two stroke and kept it around 4000 I now have a twin vee cat 26 ft with twin 140 four strokes I want to go at a fast speed but not put undo wear harm on the engines

[artdf175]

I think you should refer to by our service manual
I could be mistaken but for my 175 it refers to running at 5800-6000
You can't always do that kind of speed but don't be afraid of opening it up and let it run
You didn't state what year your 140 is
If these are new engines make certain to follow the break-in instructions
And if you don't have the service manual be sure and get a copy
Contains a lot of information no one will tell you
Art

[Fluker4]

I'm sorry they are df140 four strokes 2003 I'm not looking for top speed I'm looking to cruise as fast as possible with a correctly proper engine without doing harm with my old engine that was 4000 rpm all day long what is a safe rpm for these 4000 4500 ? Thanks mark

[Moonlighter]

Hi Mark and welcome to the forum.

Cruising revs will vary depending on the boat and motor combination. Usually, you can find a "sweet spot" where the engine seems to just lope along, without sounding laboured.

Quite often, if the motor is well matched to the boat it is on, then for the 140's, a common rev range for easy cruising is between 4000-4500 rpm.

My Df115 shares the same block as your 140 and i can cruise all day, comfortably, at 4500rpm, but it will also cruise quite happily at 5000 too. Just depends on conditions and how fast I want to go. In fact my dealer told me that every trip, i should give it a burst over 5000rpm for a few minutes just to burn iff any excess fuel in the oil and to keep it loose.

Now here's the important thing to bear in mind: you MUST select a prop for your motor that allows it to get to its max rated rpm, or close to it, when you run the engine at full throttle (WOT).

Your 140 needs to be capable of hitting 6000rpm at WOT, even though you might never again run it at such high revs. You have to test it at WOT (trimmed out) for a minute so you know for certain what revs you can achieve.

This will result in a good cruise speed at the 4500rpm as stated above, and deliver the best fuel economy AND MOST IMPORTANT OF ALL, longest engine life.

If you prop it so that it can only achieve 5000rpm at WOT, then at lower speeds the engine will be lugging (under unnecessary load) and this will dramatically shorten engine life, plus deliver poor fuel economy. And, contrary to what some people seem to think, it will be no faster at cruise speed by selecting such a prop either.

I put a sticky on this forum (see the list at the top) that more fully explains how to set up engine height and select a prop that maximises the engines performance, economy and life. Have a read, it gives you more info that will be helpful in your situation.

Cheers!