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Author Topic:   RPM's @ WOT
63WHALER posted 04-01-2003 04:26 PM ET (US)   Profile for 63WHALER  
I have a quick question, what RPM should I be reaching at WOT on a 1990 60hp Johnson this is a 3cyl. 2-stroke? The owners manual states 5000-6000, this seems broad, so what is the ideal RPM's.


JBCornwell posted 04-01-2003 06:34 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Ahoy, '63.

Light load, 6,000rpm.

Heavy load, not less than 5,000rpm.

Red sky at night. . .

Sal DiMercurio posted 04-01-2003 07:45 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
The correct way to check if your running the right prop is.
If your manual says 5 - 6,000, load the boat as you would on a normal fishing or boating trip, [ average load ], get her on plane, then trim her out as far as she can without blowing out, let her run for a few hundred yds to get up steam, then check your tach,.
The recommended best way to prop it is, allow her to reach 6,000 with an average load, trimmed out to max, this way, if you put a bigger load on her, she wont drop below & into the lugging zone.
As the post above reads, light load [ should be average load ] 6,000 rpms, big load, not below 5,000.
By proping her to reach max rpms, your allowing the engine to un-whind & produce it's rated hp, also allowing her to run much easier through out the whole rpm range.
By allowing her to get there, you will also get better fuel economy then if she only turned 4,800 or 5,000 because the throttle would be in the same place as if it was turning 6,000, but can't get there.
Confused yet ?
John from Madison CT posted 04-01-2003 07:55 PM ET (US)     Profile for John from Madison CT  Send Email to John from Madison CT     

Why does trimming the engine out so unusually far give your the true WOT RPM's.

Doesn't that really not represent the true "working" WOT RPM's of the motor. I mean, how often do we really trim her way way out like that anyway?

I personally don't know, but I've wondered this for sometime myself.



Sal DiMercurio posted 04-01-2003 09:13 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
When you take off, your engine should be trimmed in to pop you up on plane fast, after your on plane & cruising you don't want the boat to ride real flat on the water, so you trim her out till she just starts to porpoise the trim her back till she stops, this allows air to get under the boat & less drag because the boat is now riding on the last few ft of it's bottom, giving you the best speed & fuel economy & the engine works less because of little water resistance.
When testing your rpms, you need to trim her out till she porpoises then let her back down till she stops hopping along like a rabbit.
This is how you should run your rig while traveling putting the most hours on her, thats why you check your rpms at wot because most people cruise at 3/4 throttle.
When checking for rpms at max trim & max throttle, your very close to cruise trim.
If your engine is tucked all the way in, & the engine is propped right, it won't reach the desired rpm [ 6,000 ] because of to much water resistance, probably only 5,400 rpms.
But thats "not" where you should be running [ trimmed in ].
Did I loose you ?
Sal DiMercurio posted 04-01-2003 09:16 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Sorry, i pushed submit to soon.
If your engine is not equipt with t/t, set your trim pin out far enough [ second hole out ] where the boat dosen't ride flat as a pancake, yet still gets up on plane without struggling.

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