Running Johnson 60HP at 5800 RPM

[atengnr]

I received tips on this forum to prop this motor for up to 6000 rpm. Mine runs at 5800 rpm WOT..

Is it OK to run this motor at 5800 rpm for long periods of time??

Thanks.

 

[JUSTINTIME]

Re: Running Johnson 60HP at 5800 RPM

u are fine at 5800

 

[Texasmark]

Re: Running Johnson 60HP at 5800 RPM

Hi Ate.

A tidbit of info for you. I bought this boat in Dec that was originally sold in '03. That's 2 to 3 years of ownership by a guy that liked to fish (so the rig got used a lot) and also enjoyed a relaxing beverage while doing so....this tells me that he may have (probably did) lets use the word "abuse" the engine as his "gsf" probably wasn't 100% all the time.....defining abuse below.

The top end of the WOT rating for this engine is 5500. The prop on the engine was 17P, brand was Ballistic made from SS, gearbox is 2.3.

Want to talk about a hole shot; better have your neck brace on. First time out I hit the throttle for the first time and knew right away that this sucker had a prop problem; no question about it.

I had to go all the way to 24P-XP (xp has more blade area than standard Ballistics) to get the rpm's down to 5600....speed recorded with that was 52 mph on a cool day and I'm at about 700 ft altitude.

If we assume 200 rpm per inch, that translates to 1400 rpm. So for 2-3 years this engine saw 7000 rpm's I'd bet repeatedly and best I can tell it didn't hurt it a bit. It also had a stuck closed thermostat so it could have been overheated at low rpms also who knows how many times......at high rpms the bypass valve allowed for cooling.

It was a little hard to start on a cold day and being 3 cyl it idled poorly. Decarbing solved what it could of the problem.....it's still a 3 cyl and idles accordingly. Starts much faster now with the decarb.

Like I said, just a tidbit of info, a case point of one engine and what it has tolerated. Some of the guys talk on here about going to 8500 with a little tweaking and 10,000 with a lot. Sooooooo how much is too much rpm? Dunno!

HTH,

Mark

 

[atengnr]

Re: Running Johnson 60HP at 5800 RPM

Thanks for the info.

The best I can tell, the story with the 60hp is this...Its the same motor (except engine tuning - carb diameter?) as the 70hp but has a lower "recommended" operating WOT rpm (4500-5500 vs. 5000-6000). It seems to me that the reason for this is that the WOT rpm range is probably defined as the RPM @MAX HP + and - 500 rpm. So, I think the 60 hp makes 60HP @ 5000 rpm, while the 70hp makes 70 @5500 rpm.

So, I wonder, what is the negative of running the 60hp at 1000rpm higher than the peak HP?? Id love to see some dyno charts of a 60 vs. a 70 to see the torque difference at 6000 rpm.

 

[Texasmark]

Re: Running Johnson 60HP at 5800 RPM

Dhadley could probably answer your question as to just what is the difference in the two engines bein (as I gleaned from here) he used to have an OMC dealership.

I noticed also (in sales brochures) that mfgrs have two engines that appear to be similar yet one is rated for higher hp at a higher rpm. In my service manual, for example they reference different carbs and different jet sizes, and different amounts of ignition timing for what appears to be the same block of a series......none of which have a limiting impact on max rpm's from a mechanical tolerance (ability to tolerate higher rpm's) point of view.

I have speculated that the jets are just bigger to allow for more fuel to get the higher rpm's but comments have come back at me that they also tweak the porting (?) and the reed valves. Don't know without looking in a parts manual.

I'd do it in a heartbeat.......it's not like a V8 auto engine with hyd lifters, cam, cam drive chain and gears, pushrods, mechanical fuel pump, and all that stuff. Only moving parts are the crank, piston assys and rods....course the bearings turn......and the reed valves...fuel pump diaphragm. I mean just how fast can that kind of a setup turn? Ask the racers, ask D.

HTH,

Mark

 

[atengnr]

Re: Running Johnson 60HP at 5800 RPM

Dhadley could probably answer your question as to just what is the difference in the two engines bein (as I gleaned from here) he used to have an OMC dealership.

I noticed also (in sales brochures) that mfgrs have two engines that appear to be similar yet one is rated for higher hp at a higher rpm. In my service manual, for example they reference different carbs and different jet sizes, and different amounts of ignition timing for what appears to be the same block of a series......none of which have a limiting impact on max rpm's from a mechanical tolerance (ability to tolerate higher rpm's) point of view.

I have speculated that the jets are just bigger to allow for more fuel to get the higher rpm's but comments have come back at me that they also tweak the porting (?) and the reed valves. Don't know without looking in a parts manual.

I'd do it in a heartbeat.......it's not like a V8 auto engine with hyd lifters, cam, cam drive chain and gears, pushrods, mechanical fuel pump, and all that stuff. Only moving parts are the crank, piston assys and rods....course the bearings turn......and the reed valves...fuel pump diaphragm. I mean just how fast can that kind of a setup turn? Ask the racers, ask D.

HTH,

Mark

I have little doubt from what Ive read that the 60hp can safely turn at the same speed as the 70. I would just be curious to see how much less torque it has a 6k than the 70.

 

[walleyehed]

Re: Running Johnson 60HP at 5800 RPM

That engine will turn as fast as the reeds will allow...
We have needle, roller and ball bearings...as long as the engine is in reasonably good shape, you use good fuel (87oct) and the right oil and mixture, I really don't think you can hurt it...1000RPM sure won't on that engine.

 

[atengnr]

Re: Running Johnson 60HP at 5800 RPM

That engine will turn as fast as the reeds will allow...
We have needle, roller and ball bearings...as long as the engine is in reasonably good shape, you use good fuel (87oct) and the right oil and mixture, I really don't think you can hurt it...1000RPM sure won't on that engine.

I use 93 octane in 2 strokes...Does higher octane improve cylinder/ring life on the 2 strokes??

 

[JUSTINTIME]

Re: Running Johnson 60HP at 5800 RPM

the better gas means less carbon build up
also the better oil would help with build up
most manufacturers recommend no less than 87 because most engines have a compression of 170 and less
when u get around 180 u need more than pump gas

 

[walleyehed]

Re: Running Johnson 60HP at 5800 RPM

This engine will run and last longer on 87 octane...89 at most. Any higher octane is a waste of money unless manual states premium only.
The high Octane burns slower and is incomplete in the combustion process when the piston drops below the ports and allows buring fuel to escape. This leads to higher head/block temps, coking deposites beyond normal, and will fill the ring land area and can bust rings, destroying cylinders beyond repair.
Dhadley has tested extensively on this, and I have cylinder head temp and fuel flow on my V6 Rude and I have proven the RPM to be less with premium vs 87 Octane, and lower cyl head temps with 87, even though I thought it would run cooler with premium, it didn't.
We have our 91-93 octane believers out here too....I've been through a few of those engines and although I've only found 1 broken ring, most were stuck in the land.

 

[Texasmark]

Re: Running Johnson 60HP at 5800 RPM

You know Kenny, I made the same comment you did about the higher octane's burn rate several months ago, and some guy comes bashing back that it only determines how much pressure the fuel will tolerate before it self ignites (pings).

I agree that you use the lower fuel to get the BTU's out of the fuel before the crown of the piston moves into the exhaust port(s) opening.

Mark

 

[atengnr]

Re: Running Johnson 60HP at 5800 RPM

Fundamentally, this makes alot of sense. I understand that unburned fuel is bad for combustion efficiency, but why does this lead to decreased engine life??


So, 87 octane (minimum octane that prevents ping) is the best for a 2 stroke??

 

[walleyehed]

Re: Running Johnson 60HP at 5800 RPM

You have un-burnt particulates still in the piston/combustion/ring land areas.
incomplete combustion leads to coking, carbon build-up and a loss of fuel economy.
The coking is the trouble-maker, and I believe it forms because the flame front is not hot enough, quick enough to complete combustion...I also believe on the conventional 2-stroke, it deforms the shape of the cylinder/piston fit.
I think you'll hear all sorts of stories about what does and doesn't work, and why/why not.
Dhadley deals with Piston problems every day..maybe he'll step in and give his point of view as a piston expert.

 

[Dhadley]

Re: Running Johnson 60HP at 5800 RPM

Todays fuel burns hotter the higher the octane level. It's not like when we had lead and the lead helped keep combustion temps lower. Excessive combustion temps are the mortal enemy of a 2 stroke outboard. Anything we can do to help keep them in the design parameters will help the motor live longer.

Octane is one factor just like spark plug heat range, lugging, running lean, excessive compression etc. I'm not saying you can't run higher octane but you'll need to consider doing other things like going richer on the mid and high speed jets to get the temps back in line.

 

[walleyehed]

Re: Running Johnson 60HP at 5800 RPM

"Dhadley has tested extensively on this, and I have cylinder head temp and fuel flow on my V6 Rude and I have proven the RPM to be less with premium vs 87 Octane, and lower cyl head temps with 87, even though I thought it would run cooler with premium, it didn't."
.......................................................................................

Although my attempt at explaining this was not completely correct, atleast my cylinder head temp was telling the truth....
Thanks DH......

 

[Dhadley]

Re: Running Johnson 60HP at 5800 RPM

Kenny, you're seeing exactly what we see. The water temps coming up was a direct result of the higher combustion temps. You are measuring cooling water temps, we were measuring exhaust temps with an EGT gauge. The only difference is that an EGT gauge shows the changes instantly.

 

[Texasmark]

Re: Running Johnson 60HP at 5800 RPM

Now that's what I was looking for (I didn't ask the question but surely will accept and remember the answer).............hard data! Proof, not speculation.

Thanks Ken and D. Maybe we can put this subject to bed.....course it is a common concern and will come up time and time again.

A liittle off, but.......most engines run very well on today's 87 octane. I think the Dodge hemi engine recommends mid grade and maybe some high performance engines need the highest (91-92...whatever).

But around here, since 99% of the gasoline sold is 87, guess where you are going to get your freshest fuel that will sit in your (boat's) tank longer before it goes bad.

Also, I assume the higher the octane, the higher the violatility, so the hot stuff in the gas will be less prone to evaporate with the lower octane cause the hot stuff isn't so hot. d

My 2c and thanks again guys.

Mark

 

[Dhadley]

Re: Running Johnson 60HP at 5800 RPM

All grades of fuel lose their oxygenates at the same rate which lowers the effective octane. Some folks think (as I did) that higher octane (pump gas) will take longer to revert back to baseline levels because it's higher to start with. Unfortunately it doesn't work that way. The higher the octane grade, the more oxygen bearing compounds are in the fuel. But each of the compounds release oxygen at the same rate so the fuel reverts back in about the same time frame.

Now, as we modify an outboard and add compression we have to add octane at some point. But part of the mods are increasing fuel flow and getting a richer mix. Basically octane, compression and rich / lean mix all go hand in hand. Combustion temp is the way all that's measured.

Just a funny (on me) story about octane -- back in the day we were getting ready to start outboard drag racing. I wanted to get into the V4 class that was basically running stock motors. I went to an end-of-the-year 2 day race and entered a ski boat with a V4 crossflow. The idea was to just participate and see if it was something we wanted to do the next year.

We had the little ski boat running OK but had no illusion about winning. We were just going to go thru the motions and then maybe get another boat ready for the following year. Anyway, this little boat did OK and we had her turning about 6500-6600 in the 1/4 mile.

The day before we left for the race a buddy who ran stock cars offered me 10 gallons on race fuel. I was ready for fuel so I put 5 gallons in the boat and 5 in a jug. Away we went.

Saturdays race comes and I jump on the throttle the first round and get clear to (almost) 6200. Two rounds and I'm on the trailer. We work half the night trying to figure out what happened which made my wife less than pleased. Sunday, day 2, same deal. Almost 500 rpm down. The motor runs great, sounds great.

We get home and the following week I run the motor and work on it every night but never find anything wrong naturally. By now I'm about out of the race fuel and keep adding pump gas. Slowly, every day we add pump gas and gain rpm. By the following weekend we're back up to 6600. A week late. It took a week but the light bulb came on.

Obviously with stock compression, timing and fuel flow the higher octane, slower burning fuel got me.

 

[Texasmark]

Re: Running Johnson 60HP at 5800 RPM

Well there's the proof about the burn rate of fuel as a function of octane. So my grandpa didn't steer me wrong after all. d

Nice story D.

I thought you were going to say that you had forgotten to add oil to the racing fuel.....ouch! :%

Thanks,

Mark

 

[Dhadley]

Re: Running Johnson 60HP at 5800 RPM

Nope, never forgot to add oil but there were some other dumb things that surfaced over the years.........