Johnson v4 140 crossflow rpm

[Damightybigfoot]

I have a late johnson v4 140hp crossflow 1981 engine, it is propped with a 13x19p stainless steel omc prop, the engine revs at 5500rpm wide open throttle and has no issue getting to that speed... just trying to find out what other people are getting with a similar set up as a guy I been speaking too says it should easily push that prop to 6500rpm...

Hulls is a 16ft padded fibreglass hull picton 159gts.. i get 44.5mph at 5500rpm this is on a lake which is only about 1/4-1/2 mile long... out of gear the engine will rev up too 7000rpm

 

[Texasmark]

Back then 4500-5500 rpms were good numbers. Revving to higher numbers can bring engine destruction....known fact. I liked to run my engines (when properly loaded, not in N) at the max rated numbers, or thereabouts....current engine has a rev limiter so I'm stuck and it will stay but performance is more than I need at my age. The pad gets you the speed you are getting (low hull drag) but you knew that. Shooting from the hip......I am assuming that 115 rating was back before prop ratings which would mean you are really running about 100 ponies in today's prop rated terms.

Just ran a quick check at go-fast site and you are running 10% slip.....high (to me) for running on the pad. I'd think you ought to be down around 5% which would push you on up to 47. Tweaking props is a trial and error business. Design of the prop, like progressive pitch, rake, cupping, blade thickness, porting or not all make for different results for different props. Hulls response to the thrust change is undefined also...you may pick up some mph because you improved you slip, or because the hull was more efficient as speed was increased. You may change the transom angle with shims to get the engine to trim out higher (without blowout) and get some more mph........

 

[Faztbullet]

as a guy I been speaking too says it should easily push that prop to 6500rpm...

Sorry but that guy is uninformed....

out of gear the engine will rev up too 7000rpm

Means absolutely nothing ..runs risk of runaway and blowning engine as NO LOAD!!. That motor is rated 115HP so you are close to what its going to do. You can play with some props to see if you can tweek a few more MPH out.

 

[Damightybigfoot]

Back then 4500-5500 rpms were good numbers. Revving to higher numbers can bring engine destruction....known fact. I liked to run my engines (when properly loaded, not in N) at the max rated numbers, or thereabouts....current engine has a rev limiter so I'm stuck and it will stay but performance is more than I need at my age. The pad gets you the speed you are getting (low hull drag) but you knew that. Shooting from the hip......I am assuming that 115 rating was back before prop ratings which would mean you are really running about 100 ponies in today's prop rated terms.

Just ran a quick check at go-fast site and you are running 10% slip.....high (to me) for running on the pad. I'd think you ought to be down around 5% which would push you on up to 47. Tweaking props is a trial and error business. Design of the prop, like progressive pitch, rake, cupping, blade thickness, porting or not all make for different results for different props. Hulls response to the thrust change is undefined also...you may pick up some mph because you improved you slip, or because the hull was more efficient as speed was increased. You may change the transom angle with shims to get the engine to trim out higher (without blowout) and get some more mph........

Id be happy with 47mph... i need to get it out on the sea to test properly the full speed....

 

[Damightybigfoot]

Sorry but that guy is uninformed....

Means absolutely nothing ..runs risk of runaway and blowning engine as NO LOAD!!. That motor is rated 115HP so you are close to what its going to do. You can play with some props to see if you can tweek a few more MPH out.

the engine is 140hp not 115hp... i am aware of risking run away, I did wide open for a few seconds out of gear just to make sure the engine revved correctly wasn't running badly!

 

[Damightybigfoot]

Back then 4500-5500 rpms were good numbers. Revving to higher numbers can bring engine destruction....known fact. I liked to run my engines (when properly loaded, not in N) at the max rated numbers, or thereabouts....current engine has a rev limiter so I'm stuck and it will stay but performance is more than I need at my age. The pad gets you the speed you are getting (low hull drag) but you knew that. Shooting from the hip......I am assuming that 115 rating was back before prop ratings which would mean you are really running about 100 ponies in today's prop rated terms.

Just ran a quick check at go-fast site and you are running 10% slip.....high (to me) for running on the pad. I'd think you ought to be down around 5% which would push you on up to 47. Tweaking props is a trial and error business. Design of the prop, like progressive pitch, rake, cupping, blade thickness, porting or not all make for different results for different props. Hulls response to the thrust change is undefined also...you may pick up some mph because you improved you slip, or because the hull was more efficient as speed was increased. You may change the transom angle with shims to get the engine to trim out higher (without blowout) and get some more mph........

As I've been on the lake which is a bit small I've been struggling to get it to get onto the pad... its sitting with a fair bit of wetted hull not sitting on the pad properly, I'm going onto the sea next week, any advice to getting onto the pad properly? From moment I plane I get a rooster tail trimming up steering goes stiff as trimmed too far before it blows out but again I cant get onto pad before it goes stiff

 

[Texasmark]

Now I see you are talking about a 140. Significant change in comments...give me some time to do some research and I will come back on this.

 

[racerone]

Step #1 is always a compression test on these crossflow motors.----No idea why anyone would rev these motors to 7000 RPM in neutral.------They will rev that high on 3 of 4 cylinders !!

 

[Damightybigfoot]

Now I see you are talking about a 140. Significant change in comments...give me some time to do some research and I will come back on this.

I eagerly await your reply

 

[Faztbullet]

the engine is 140hp not 115hp..

It is powerhead rated 140 and 115 at prop... The later 115's are identical to your motor. Post a pic of prop and height motor is setting..

 

[Texasmark]

I eagerly await your reply

In back tracking my comments, I see that I missed your 140 hp engine size....I usually work 115s and just had a brain pfart I guess.....getting to be more frequent at 79.

Plug this into your search engine. The responses will be informative....at least one: "Top speed for Johnson V4 140 hp outboard?"

 

[Damightybigfoot]

It is powerhead rated 140 and 115 at prop... The later 115's are identical to your motor. Post a pic of prop and height motor is setting..

We raised it up from half inch above bottom of hull as it was cavitating like mad, chine walking and porpoising, where we raised it too eliminated all of that!

Prop is a 13x19p omc ss part number 389510, however it had a few dings in it so I cleaned and sharpened the edges and polished the prop to a high shine finish

 

[Damightybigfoot]

For some reason it only uploaded the one photo...

 

[Damightybigfoot]

In back tracking my comments, I see that I missed your 140 hp engine size....I usually work 115s and just had a brain pfart I guess.....getting to be more frequent at 79.

Plug this into your search engine. The responses will be informative....at least one: "Top speed for Johnson V4 140 hp outboard?"

See using a slip calculator it says the only problem i have is it slips too much.... that post is about going from a 115 to a 140 on a smaller boat completelt different style hull aswell so its hard to judge

 

[emoney]

I can't imagine that 5500 rpms isn't pretty much what the Factory Service Manual says. I would definitely not be pushing 7k in the driveway, that's for sure. Have you weighed the hull to make sure you don't have some serious water intrustion? Water weight absolutely affects performance and for some reason, it's the last thing checked.

 

[Damightybigfoot]

I can't imagine that 5500 rpms isn't pretty much what the Factory Service Manual says. I would definitely not be pushing 7k in the driveway, that's for sure. Have you weighed the hull to make sure you don't have some serious water intrustion? Water weight absolutely affects performance and for some reason, it's the last thing checked.

Done a full inspection on hull, its solid, no rotten wood, not water weight e.c.t I did it once in water out of gear judt to make sure it did rev and it hadn't got a limited cdi on it... i believe it does 5500 in manual but I am just worried as a few people have said they get 6500 with my prop, there's even people running 23pitch props with 6000rpm on a stock block and I'm getting 5500rpm with a smaller prop.... id be happy if I could run near 50mph and honestly im not far off that I'm running 44.5mph and thats with roughly 10% slip, taking onto the sea on Sunday so will have chance to fully open it up just trying to find out what people are running with a similar set up so I know its performing correctly and not just me over thinking

Another thing that concerns me is my brother has a deep v hull with no pad, 17ft mines a 16ft and he has a mariner 90hp with a 2.3:1 gear box mines 2:1 also he has a 18p prop... he runs 42mph where I run 44.5mph with bigger set up and power and a more race style hull... havent yet worked out his prop slip as I've gpsed his boat but never took rev reading (never bothered me until I got mine)

 

[He rik]

44,5mph is approximately what I got with a 13x19p prop as I remember on mine 40knot/46mph at 5500, 16ft/115hp -82.

If I remember correctly your WOT range should be between 4500-5500 as mine but I cant find the chart again to doublecheck and I remember there where a few engines with another wot-range, cant find any numbers where max.effect is but if its as an ordinary two-stroke it drops significally after max effect, say max at 52-5300 or so with a wot up to 5500, but Im just guessing here, Im not familar with ouboards yet.

Either your engine "flats out" at 5500 or you got a few ponys less in it, mine stopped at 5500 but should theoreticly rev to 5700 (200r/inch) as I run a 21p at 5300, but I have a 115 (Im actually not sure about 21p but the numbers dont add up on anything else)

And if I understand this right (Im new to this) you have to reach almoast 5650 if you want to reach 50mph without any slip at all and 5850 with 5% w 19p, all in theory...and again, if I understand this right.

 

[Damightybigfoot]

44,5mph is approximately what I got with a 13x19p prop as I remember on mine 40knot/46mph at 5500, 16ft/115hp -82.

If I remember correctly your WOT range should be between 4500-5500 as mine but I cant find the chart again to doublecheck and I remember there where a few engines with another wot-range, cant find any numbers where max.effect is but if its as an ordinary two-stroke it drops significally after max effect, say max at 52-5300 or so with a wot up to 5500, but Im just guessing here, Im not familar with ouboards yet.

Either your engine "flats out" at 5500 or you got a few ponys less in it, mine stopped at 5500 but should theoreticly rev to 5700 (200r/inch) as I run a 21p at 5300, but I have a 115 (Im actually not sure about 21p but the numbers dont add up on anything else)

And if I understand this right (Im new to this) you have to reach almoast 5650 if you want to reach 50mph without any slip at all and 5850 with 5% w 19p, all in theory...and again, if I understand this right.

See one my theories too the 140 5500rpm matching the 115s with a 19p is that the 19p maxes out and cant push any more... its the same gearbox as the 115s so that would explain why it doesn't see more... but thats a hard one too prove... if I put a bigger prop on I might see more rpm and the prop won't max out but lose acceleration... and I already struggle with the accwlation with a skier at the moment...

 

[He rik]

See one my theories too the 140 5500rpm matching the 115s with a 19p is that the 19p maxes out and cant push any more... its the same gearbox as the 115s so that would explain why it doesn't see more... but thats a hard one too prove... if I put a bigger prop on I might see more rpm and the prop won't max out but lose acceleration... and I already struggle with the accwlation with a skier at the moment...

accwlation? you meen cavitation?

How is your bottompaint? Crusty?
Anything else than a smooth bottom can disurb waterflow and can cause cavitation.

Or do you meen acceleration?

If so, check the engine, I have absolutly no problem to pull skier or wakeboard, if any too much power so some skiers cant hold on until they are up if I push to hard on the throttle.

 

[racerone]

I believe there are some tutorials online ------Have details on acceleration / slip / diameters / pitch / 2 blade / 3 blade / 4 blade.------Explains thing like 90 / 115 / 140 all with the same gear box ETC , ETC