What rpms should my 1993 115 Johnson run at?

[lainjustin]

I have a 93 115 Johnson. Recently bought the boat ( which is a 18 ft nitro) and I am wanting to upgrade to a stainless steel prop. Seeing as how I definitely don't want to waste my money by buying the wrong one I am trying to figure out what to buy. My boat runs 40 with me in it tilted up for for mph and at 6000 rpms with a 13 1/4 by 17 aluminum prop. I know I need to bring that down some ( although I don't know exactly what the specs of my exact motor are) and I heard for every pitch you go higher its like 200 rpms less. So does that mean I should get a 19 pitch prop. Help me out. Ive looked at threads for hours and haven't gotten the concrete answer I am wanting before I spend the money.
My model number is J115TLETS in case it matters

 

[emdsapmgr]

Re: What rpms should my 1993 115 Johnson run at?

Sometimes changing a prop from 17 to 19 will decrease rpm's by up to 300. Probably where you want to go with your next prop (19). Your engine is hp rated at 5000 rpm's. Normal operating range is 4500 to 5500. Current thinking is that the engine should run in the upper range of the normal operating range, or 5500. Your model is the bubble back engine which does breathe better at higher rpm's. It will still make good, reliable hp up to 5800 a good target rpm for your next prop. If you do get into stainless props, you may be able to further improve WOT performance by raising the engine somewhat on the transom. That becomes another factor to consider when purchasing the correct prop pitch.

 

[TD_Maker]

Re: What rpms should my 1993 115 Johnson run at?

For me, there would be a couple of things to consider.

You mention that your motor is hitting 6000 RPM with you in the boat. What fuel load are you carrying at that time? Do you ever fish with a partner? If so, what are you turning then? Are you always running wide open throttle? If it were me, I would keep the 17 and back off the throttle a little. Its better to have it....and not need it, than it is to need it...and not have it. Just my humble opinion.

 

[racerone]

Re: What rpms should my 1993 115 Johnson run at?

Most dealers will have a 21" pitch prop to try.----Agree to buy a prop is all that it takes.------------Too much risk in running that motor at 6000 RPM.

 

[lainjustin]

Re: What rpms should my 1993 115 Johnson run at?

For me, there would be a couple of things to consider.

You mention that your motor is hitting 6000 RPM with you in the boat. What fuel load are you carrying at that time? Do you ever fish with a partner? If so, what are you turning then? Are you always running wide open throttle? If it were me, I would keep the 17 and back off the throttle a little. Its better to have it....and not need it, than it is to need it...and not have it. Just my humble opinion.

It will run 5800 with me and another fisherman with me, a small cooler, and half a tank of gass. I use my boat 99.9% of the time to fish, either for fun or in tournaments. I could keep the 17 pitch prop for use for tubing or skiing later in summer, but my primary goal would be to bring those rpms down so I don't hurt anything as I know I am over the specs. Fishing in tournaments a lot I will need as much speed as possible for getting to spots quicker. Therefore I would have it WOT a lot.

 

[emdsapmgr]

Re: What rpms should my 1993 115 Johnson run at?

5800 is ok. I also ski with one prop and change to another for general boating. If you are considering a stainless prop, be aware that they perform slightly different. Usually you consider a stainless prop is one pitch higher than stamped on the prop. IE, a 17 stainless will usually perform more like an 18 pitch, yielding slightly lower WOT rpm's than it's 17 pitch aluminum brother.

 

[V153]

Re: What rpms should my 1993 115 Johnson run at?

Provided your tach is accurate, I'd stay right about where you're at. Try a 19 Raker or Laser or Lightspeed. Mebbe a Ballistic though they've never worked that great for me. I think a 21'd be a lil too tall.

"Try before you buy" is kinda a thing of the past, down here at least. Musta got burned by an ahole one too many times. Now it's buy it, try it, if'n ya don't like it we'll getcha nuther one.

Remember motor height has a lot to do with top end too. Post a pic of your set up. I'd think the boat should be runnin closer to mid 40s as is.

6K is nothing for those motors. I had a virtually stock '86 90 that I routinely revved 62-6300 rpms. Not all day, but just sayin'. That motor'd still be running if the water jacket hadn't failed.

Rpm = HP in those motors. I'd shoot for 5900 to 6K WOT. Use good oil'n gas'n don't run it there for hours on end & y'oughta be okay.

 

[toddschubert]

Re: What rpms should my 1993 115 Johnson run at?

I wouldnt run that motor more than 5000 rpm regardless if you have to go 40 mph get a bigger motor.

 

[emdsapmgr]

Re: What rpms should my 1993 115 Johnson run at?

The factory stated normal operating range is 4500-5500, right from their product information specs. Should be no problem for that bubble back performance engine to make good hp up to 5800.