Prop/RPM help for a DF140 on a Key West 2020CC

[Auburn02]

I've had prop discussions on other forums over the last few years regarding my 2003 20' Key West with a 2003 DF140 on it. When I bought the boat 5 years ago, I had to battle some performance issues themselves (replaced all filters, had injectors cleaned) and then had to address the prop, as it only had a Michigan 13x19. I wound up settling on a Powertech LNR3 14x20, but I think I'm over-propped since I can only hit about 5500-5600 RPM running full speed and trimmed out.

That said, I also decided last year that my motor was too low. The anti-ventilation plate was just below the keel, and when running it was buried in the water. Also made it very hard to steer at speed. Over the last couple of weeks, I raised it two holes on the transom. Doing so resulted in much better steering, but too much/too easy blow out in turns, so I lowered it back one hole and feel the motor height is about right now. What's odd (to me) is that even with those changes, I didn't pick up any RPM. My max RPM with a usual load - two people, ~50 gallons - has stayed pretty consistent at 5500-5600. That leads me to the conclusion that I'm a bit over-propped still, but also that perhaps I have another fuel obstruction issue where I'm not getting full power from the motor.

Is it a crazy idea to try and rev to motor to redline in neutral, just to see if it can reach 6000-6200 RPM without the load of the prop in the water? Or is that a scary/bad idea? Point being I don't want to go down on the prop pitch if the problem is that I'm not getting full power out of the motor in the first place.

And my next question, if I do decide to drop to a 14x19 prop, won't that raise my cruise RPM for a given speed? Is it worse to be slightly over-propped but be able to maintain a 30 mph cruise at ~4300 RPM, or to be propped correctly for max RPM but then have to spin ~4600 RPM to maintain that same 30 mph cruise?

Of course I know Suzuki does not make a 14x19 stainless prop, but would probably opt for the Powertech LNR3, which is what I have now in the 14x20.

I appreciate any help/suggestions you guys might have. Wish I had known about this forum when I first got the boat so I could have come straight to the experts then!

[Moonlighter]

Hi there and welcome to the forum!

A couple of thoughts.

First, that's a pretty big boat to be pushing with a 140. So propping will be a challenge, but should be doable. That may explain to some extent the lack of extra revs with the engine lifted.

You should truly aim to get around 6000rpm at WOT, trimmed out. Even a bit more than that with a light load. These engine love to rev, and indeed, the perform best when they are allowed to rev.

Re revving in neutral, yes, it's a bad idea, and in any case, you won't be able to because the Suzuki has a rev limiter in neutral that prevents this from happening. It will get to about 3000rpm then it will splutter and carry on as the rev limiter interrupts spark and restricts fuel to the injectors.

Next, getting the engine propped right so that is revs out to 6K at WOT is all about gearing the engine to optimise performance and economy across the rev range.

It is false to assume that decreased revs at cruise speed = better economy. Why? Because you will be running the engine with more LOAD on it than is optimal. And running the engine constantly under excessive load increases wear and tear on internal components and greatly reduces engine life. Which is bad.

So yes, you might find that to cruise at your preferred speed requires a few more revs, but the fuel economy will almost certainly be better. Hole shot will be better, and you may even pick up some top end speed too.

Specifically, to answer your question, yes, it IS worse to over prop and lower cruise speed than it is to increase revs at cruise speed. Much worse. One of the things we always look at is the engine printout which shows how much time the engine has spent in the various rev ranges during its life to date. Always are very wary about any engine where the record shows nil or very little time above 5000rom and none above 6000 - it's a sign of an over propped engine which means trouble is not far away.

Re your prop options, one inch of extra pitch will only give you about an extra 200rpm.

You need to get from the current 5500 up to 6000rpm, so you will want to go to at least an 18" pitch rather than to a 19". (By the way, I am not surprised at all that the 20" prop is too big for your boat/motor - I run a Suzuki SS 3 x 14 x 20 on my DF115 on my 17 1/2 foot boat and pull 6200. It's a popular prop on the 115/140's on many boats around the 17-18ft length, so on your 20 ft boat.....)

I don't know about the power tech props, but for comparison purposes might be best to stick with them as changing makes can change performance quite markedly.

My recommendation is to try the 18". And not to worry at all if you have to rev more to cruise at your prefers speed.

Cheers

[Auburn02]

Thanks for taking the time to type all that out! My only hesitation and something I failed to mention in my post, is before settling on the 14x20 I did try a 14x19, and the motor was over-revving to close to 6400. Then I went to a 14x21 and Dropped drastically to 5500. After that I dropped again down to the 20" pitch and only picked back up 100 RPM at the most. I was told that unfortunately the Powertech props just aren't that consistent and in hindsight I should have stuck with the 19" and maybe added some cup to it and thus the reason I'm considering a 19" again, though I completely understand your suggestion of an 18" pitch given my current results. In any event, I'm also concerned about the motor being able to achieve full power even with the right prop because of the fuel obstruction issues I battled when I first got it. That may all be in my head now though.

My boat is a light 20' but I do agree that in hindsight is on the larger side for this motor. And I tend to tanker a full 60 gallons even though that's not at all necessary for where we go with the boat. I need to get in the habit of maintaining about 1/2 tank. But like you also alluded, I would benefit from increased holeshot with less pitch and that would be very helpful.

[Moonlighter]

No problems. Glad to help.

Gee, you must have got a rogue prop with that 19" one that you tried, it must have been more like a 16 or 17. That is seriously wrong, for one inch of prop to make such a radical difference. It really makes picking the right prop a lottery if those Powertech props vary so radically.....

If you have a good local Suzuki dealer, or a good prop shop, maybe ask if they have any test props that you can "try before you buy". If they've got a stainless 14 x 18 or even a 14 x 20, you could try one of them, and you'll then have a decent baseline to work from to pick the right prop. A consistently shaped, pitched and balance prop does make a nice difference! :

Solas make a pretty reasonable stainless prop for Suzukis, might be worth a look there. I don't know about the U.S., but here in Australia Solas will recommend a prop to suit your boat, you buy it and they ship it to you. Then, if you aren't happy they will exchange it with you, several times if necessary, until you get the one you are happy with.

Good luck!

[Auburn02]

Yeah, I'm starting to think I'd be better off playing with a more consistent prop like the OEM Suzuki ones. I'm also thinking about trying the Michigan 13x19 I still have that came with the boat, see how it spins up with that one compared to my current setup. That should help me narrow down if I'm getting full power at least, and who knows I might even like it more.

[Grumpy56]

My son has a KW 2020CC with a DF140. Boat is a 1999 and the engine is a 2005 with 150 hours. We took the boat out a few times last weekend, but it was too rough to run very fast off the Texas Gulf coast. The prop on the boat is a Rapture (I never heard of them) 13.25 x 17. I do not know what RPM the engine will max out at with that setup, but with 2 people , 40 gallons of gas, it runs at 26 MPH at 4400 RPM. Seems to be a little slow to me. We have owned the boat since March, second owners.

I find you comments interesting about PowerTech. I own a Pathfinder and on the Pathfinder forums PowerTech props are very popular. I know they make a BUNCH of different props (it is more then just diameter and pitch), so maybe you do not have the right version of prop for your boat. If you are interested in PowerTech call their tech support and talk to Marcus, he is “the Man” when it comes to matching type of prop to the type of boat (hull style, weight, expected performance like mid range crusing speed or holeshot....)you have.

We have a few more things to get done on the boat before replacing the prop, so please keep me informed with your progress.

Craig

[Auburn02]

Craig, I didn't mean to make it sound like Powertech makes a bad prop, I was just told by a reputable shop that they may not be as consistent in pitch and cup as the Suzuki props. The Powertech LNR3 is a clone of the Suzuki OEM props, but I went from a 19" pitch to a 21" pitch and lost about 800 RPM with no other changes, hence the inconsistency. Still a good prop I think, just hard to compare one size to the next.

Is 4400 RPM the max you guys can get out of the motor? With that small prop I'd expect full throttle to be at or above the recommended Suzuki max of 6200.

I haven't used the boat since I last posted, but I do plan to take my Michigan 13x19 down with me and give it a shot hopefully soon and will report the results. Really I want a Suzuki 14x18 to try, but I'm not going to spend $400 for a new one just to tinker.

[Grumpy56]

Auburn,
I don't know the exact max RPM of the engine but it is in the 6K+ range. I know the engine (it is running great) can swing a larger prop, just have not got to it yet. My son has the boat and he is a machinist that makes equipment for oil drilling. Right now they only have 2 machinist left, down from 7, and are only working 32 hours per week. Once they get back to 40 hour weeks, he will have some spare cash to upgrade the prop. Let us know how you prop upgrade is going.

[Auburn02]

So as a brief update, I went back to the Michigan 13x19 prop I have. As expected, it slips like hell (~19% at 6300rpm/39 mph), but the motor revs up FAST. And at full throttle and trim, it creeps past the 6300 RPM max - this is good news to me, as I was worried I might have a fuel/airflow restriction again that was limiting the engine, but appears to be all in the prop bogging it down. I'm still going to replace the filters this off season and try to pull and clean out the VST, but will leave the injectors alone.

Now I really want to get my hands on a Suzuki brand stainless 14x18 prop for this engine. Feels like that should be the sweet spot. If it comes up a little under-propped still, I could see about having a shop just add some cup to it. I'm just too cheap to order a new one quite yet. If anyone here has one, I may be interested. In the meantime I'll keep an eye on ebay.

[Grumpy56]

Auburn02, Thanks for the update. My son still has not done anything with his prop, to busy fishing. When he does, I will post any results he gets.

Craig

[Solarman]

Auburn, google this to see if anything shows up for you, reasonably priced I hope?
It doesn't just cover Ebay, but anywhere someone posts one.

Suzuki 14x18 stainless prop


good luck.

[acdiii]

Suzuki Prop

I have a Suzuki 3 blade, 14 X 18 in excellent condition that I ran on a DF 140. let me know if you are still looking for one.

Andy

[briscoe]

What area of country do you live in?

I have a 2020 Blazer Bay with a DF140. I started with a 14x22, which it came with. No hole shot and it trimmed out at 5600 rpm, as I recall.
I took my boat specs and prop to Baummons Propeller Service in houston. Short story, he repitched mine to 20". It was $100. They do props for ships worldwide.
My boat leaps out of the hole, turns 6100 rpms at WOT and trims out wonderfully.
18 or 19" seems way too low and will over perform. I think max rpms is 6200. BTW outboards are desgned to run at WOT. They have over rpm protection, but it doesn't hurt them to run WOT. It may hurt your wallet, but underperforming is worse.
You may just want to repitch.
Briscoe

[Auburn02]

I have a Suzuki 3 blade, 14 X 18 in excellent condition that I ran on a DF 140. let me know if you are still looking for one.

Andy

Wish I had seen this earlier, but just this week I pulled the trigger on another 14x18. Actually was just coming back to this thread to re-read the suggestions and input as I was second-guessing that I ordered the right prop.

briscoe, interesting to hear about your experience. Must be the hull design that makes the motor spin up easier on your boat, being a bay style vs. offshore/deeper V on my Key West Bluewater. With a 20 I'm way over still, despite confirming/correcting the motor height it was still barely hitting 5600 with a light load and lugging out of the hole as well.

Looks like I never updated this thread, but late last season I swapped back to my old 13x19 Michigan propeller, and confirmed the motor can still turn over 6000+ when the prop is not overloaded, it was just slipping like crazy out of the hole (RPM shoots up, then levels out). So that helped my decision to try the 14x18 for the all around best fit. We shall see when I get it in the water in a few weeks and I'll update here with my findings.

[Auburn02]

Got my new prop but haven't installed it yet - anyone know where to buy vent plugs for Suzuki props? I didn't even realized the Suzuki props had the ventilation holes in the hub, and I'd like to have some plugs on hand to experiment with when I get the boat in the water. Considering the presence of the holes, I'm finding it oddly difficult to even find the plugs to buy.