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Rigged a new DF140 on a 1975 20' Mako and did the break in. I know some will think the boat is underpowered but the 140 pushes it with no problems and is a very common set up here. More importantly, the 1975 hull was rated for up to a 200 2 stroke (which weighed just over 420lbs) and the DF140 is the closest in weight in regards to new 4 strokes that will push her. Once I got through initial break in stages I opened it up to test prop rpm. I selected a 4 blade Solas 13x19. I ran the boat with just me, no extra gear (the boat does have a large T-Top), and only about 12 gallons of fuel. I am in the process of refinishing so I was also short the I pilot trolling motor and two large batteries so maybe another 180lbs light. I generally would have two more people on board and fishing gear so add another 400 lbs. The boat easily hit 6200 RPM and if I trimmed up I could get it to approach 6300 RPM (which I did only for the time it took, maybe five seconds). Recommended max for the engine is 6200 RPM but I feel that with actual loads I have the right prop. The boat handles better at low speed than my old motor and prop set up, jumps up on plane, and seems to have good thrust all through the power band. Speed topped out at around 36mph (57 kmh). I generally don't run the boat wide open and tend to fast cruise at around 5000 RPM when I'm trying to get somewhere . Does this all sound good? Isn't it better to be able to reach maximum RPM than have a loaded engine? As the engine breaks and loosens up will RPM increase enough to require a prop change? Thoughts?
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You do want the engine to get close to max rpm in order to perform well and have a long and happy life. The rev limiter will kick in if you over rev. So your rev range at present looks fine to me.
Yes they will loosen up a bit and gain a few rpm after 80-100 hours.
Now, normally the 115/140’s would run a 14” diameter 3 blade prop, and the Suzuki 14 x 20 SS prop just seems to be a very popular and effective prop for many boats with those engines. Whether it would suit your 20 footer is of course another thing.... -
Correction- the prop is in fact a 13.75 x 19. Big difference! I bought an aluminum to test but now the concern is how a SS model will "act"? What can be expected switching to stainless?Comment
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