Is 4200 rpm wot bad for a motor

[fish4970]

i have a 1987 suzuki 85 HP<br />that runs at 4200 rpm with a 13x19 prop<br />the boat is a 18' skeeter <br />it planes fine & runs 42mph<br />gets great fuel economy <br /><br />is this rpm too low for this motor<br />what would be the downside of it

 

[ob]

Re: Is 4200 rpm wot bad for a motor

I would say that 4200 rpm is 1000 short of where your engine should be propped to turn at WOT.Overpropping causes the engine to be overworked or essentially (lugged) coming to speed.If you know that your tach reading is accurate I would recommend trying a different prop of reduced pitch.Your engine will last longer.

 

[fish4970]

Re: Is 4200 rpm wot bad for a motor

I am fairly new to outboards <br />please explain what is luged<br />& what damage it does<br />if i do the math 5200 rpm is this the corect rpm?

 

[ob]

Re: Is 4200 rpm wot bad for a motor

Lugging an outboard by overpropping can be likened to climbing a grade in an auto engine in high gear.It will lead to excessive carbon deposits,overheating, and cylinder loading.Performance will also be sluggish on throttle up.In short,you are presently overpropped.

 

[fish4970]

Re: Is 4200 rpm wot bad for a motor

THANKS OB<br />for the info i have a 13x16 that runs about <br />5300rpm that i will go back to and just live <br />with 30 mph instead of the 42 that i was getting<br /><br />but it sure beats the alternitave of a blown<br />engine

 

[fish4970]

Re: Is 4200 rpm wot bad for a motor

OB is it true that a lot of poepole are<br />starting to run suzuki in that area

 

[ob]

Re: Is 4200 rpm wot bad for a motor

You see more than you did 10 years ago.For the most part John/Rudes and Yammies.Overall there is a wide spectrum of outboard brands on the water nowdays.

 

[what200]

Re: Is 4200 rpm wot bad for a motor

4200 at WOT is bad for the motor.<br /><br />At this RPM - with the thottle butterfly all the way open - allows more time for air/fuel to pack in to the cylinders. This produces max power but also leads to high combustion temps which can lead to detonation if allowed to run this way on a continuous basis.<br /><br />Sumthin don't jive with your rpm/pitch/speeds. Do you have another tach to verify the reading?<br /><br />If the tach is right, you should be getting similar speed with the 16. What is your lower unit ratio?

 

[chris in va]

Re: Is 4200 rpm wot bad for a motor

I know my Suzuki DT75 with a stock 13.5 x 15 prop runs WOT at 5400, around 38mph. Awesome hole shot, sorta low on top end, but oh well. It'll scoot that 16' Jason around just fine.

 

[donlee]

Re: Is 4200 rpm wot bad for a motor

Sounds like your tach, speedometer or both are giving you some bad info. your 16" pitch prop will give you only 84% distance per rev. of your 19" pitch, but at 5200 vs 4200 you are getting 24% more revs. Net result is same speed. Unless your old 16" is slipping, or it is not 16" pitch. If it was 13" pitch you would drop to approx. 35 mph.

 

[fish4970]

Re: Is 4200 rpm wot bad for a motor

Sorry I gave yall some bad #s<br />It's a 13.5x15 that runs 5200 rpm and 36 mph (GPS)