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Author Topic:   Recommended continuous RPM
penningtonjeff posted 07-13-2007 01:28 PM ET (US)   Profile for penningtonjeff   Send Email to penningtonjeff  
I can't find a recommended continuous-use RPM number in my ETEC owners manual. Do other outboard manufacturers give a recommended RPM for continuous use? Diesel engines have both a continuous and max RPM rating, cars have a 'redline', you'd think there'd be the same for an outboard. Am I missing something?

I read somewhere on here, quite possibly from one of Judge/Bigshot/Tosgib's split personalities that 75% of max rated RPM is a good number, which seems reasonable (follows the 80/20 rule).

Rented a boat with a Yamaha 50 four stroke last summer and asked 'what should I keep it under', and the marina guy said 'go wide open! doesn't matter with these things.' Can't believe that.

Bella con23 posted 07-13-2007 02:22 PM ET (US)     Profile for Bella con23  Send Email to Bella con23     
My RPM "sweet spot" is the fastest speed at the lowest gallon per hour ratio. Running the boat wide open won't hurt the engine on the short term because with the proper sized prop the RPM will remain under the manufactures "red line". It will however suck up the fuel.
Peter posted 07-13-2007 04:49 PM ET (US)     Profile for Peter  Send Email to Peter     
My 225 Fichts have a redline of 6000 RPM and are propped to reach close to that. At cruise, I typically run them at 4000 RPM where they are quiet and fuel efficient. 2/3 to 3/4 throttle is typically the recommended setting for cruising and in my set up, the optimal and most comfortable cruising speed falls right in line with that. E-TECS shouldn't be any different.
Sal DiMercurio posted 07-14-2007 11:00 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Jeff, you don't give what hp your e-tech is, but 5500 rpms should be real close to recommended max rpms, if your close to a 75 hp.
I believe the bigger 150s - 250s are either 5800 or 6000 rpms.
You "DO" want to get as close to the factory recommended "maximum" rpms as possible, not the low end.
I get e-mails all the time from people wanting to prop their engines to only turn 4000 rpms max., in order to save on fuel & not wear their engine out,....man, that couldn't be farther from being right than running the engine on paint thinner.
If you prop your engine so it can't reach "AT LEAST" to the mid range of the factory recommended rpm range, your asking for major problems in the very near future on that engine.
You will get your best fuel economy & performance from your engine, if you prop it so it "CAN" reach it's recommended red line, but only run it at 1/2 to 3/4 throttle.
Sal
Tohsgib posted 07-14-2007 01:11 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
I read somewhere while waiting for my Shrink :) that if you run WOT you will only get 10% of the engines intended life. With a diesel you may only get an hour. They say 75% or so with gas and 90% with diesel is Ok to get max engine life, not necessarily max MPG. I always say run them where they are happy and MPG and speed are good for you. My 115 redlines at 6k and I run her at roughly 4-4200 which is a good cruise(25ish) and fantastic fuel economy. Some might say I would get better MPG at 35-3800 but on my boat she is kinda struggling at that speed and at 4000+ she is level and cruising along. My prop is also a tad underpitched and I will hit 6200. With a larger prop I might get a decent 3800 cruise but honestly I doubt I will get any better MPG and I am happy with the way she is. I am currently running a 20" and am trying a 22" on it now. I like the performance, but I have not run the GPS to see if it really makes sense to swap. Anotherwords if performance numbers do not change much, what difference will running 66% throttle with one prop and 66% with another really make just because rpms are a couple hundred different?

On the flip side, rental boats get run WOT constantly and they seem to get some years out of them. Does not mean they would not get 2 or 3 times more life if run conservatively. The other thing is that even if you run WOT all the time, does not mean you are running WOT all the time, you do have to dock or slow down some time. My friend Dave used to run mashed to the dash no matter what in his Newport but he bought a new engine every 3 years and man did he suck down fuel but we made it there quickly....and scared to death.

Tohsgib posted 07-14-2007 01:17 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
PS...I love questions like this because somebody will say NEVER run more than X-RPM. Well that might be true for your engine but what about this:

Engine redlines at 6k so 4500 is a good fast cruise.
Engine redlines at 5500 so is 4500 still a good cruise?
Engine redlines a 5200 is 4500 still a good cruise?

Now flip that and say:
Engine redlines at 5200 and I cruise at 3500.
Engine redlines at 5500 can I actually cruise at 3500?
Engine redlines at 6k, can barely stay on plane at 3500.
Engine redlines at 6300, can't stay on plane at 3500.

What is good for the goose is not always good for the gander.

penningtonjeff posted 07-17-2007 11:18 AM ET (US)     Profile for penningtonjeff  Send Email to penningtonjeff     
So the answer is use common sense and listen what to the boat/motor tell you.

It can't be that easy.

Sal, it's a 50, propped to max out at 5600, which it does regularly. that's within the max operating range (5500-6000), though at the low end.

Egdujeht, mine is happier at 4000-4250 too. At that speed, she generates enough lift so that I can trim the motor out without dragging her stern. There's a bit of work with the throttle because:

- she cruises on level plane at 4200
- I trim the motor out and she goes faster and the RPMS go up to 4500.
- I throttle back to 4250 with the motor still trimmed out
- Sometimes, if I throttle back too far, she starts to drag.
- Start all over again

Common sense tells me that even if the motor is at the same throttle setting, if the RPMS go up due to changing trim, it's 'bad' for the motor.

I got the 7 year extended warranty, so maybe all this is hot air and I should just run her at WOT and hope for a big bonus in 2014.

penningtonjeff posted 07-17-2007 11:20 AM ET (US)     Profile for penningtonjeff  Send Email to penningtonjeff     
Correction - max range is 5500 - 5800, not 5500-6000.
Tohsgib posted 07-17-2007 12:28 PM ET (US)     Profile for Tohsgib  Send Email to Tohsgib     
Yes it is that easy and you just admitted it in your last post. Yes she goes up to 4500 and is "breathing easy" then you throttle back to running her at 4250 trimmed is probably where you want to be. She is TELLING you I want to run where it is the easiest and most fuel efficient to do so. Keeping her trimmed in so you RPM's are lower makes no sense and is defeating the purpose of getting her in her sweet spot. 4300 cruise is fine, I run my 115 there all the time and do it the same way you do yours...perfect.

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