Prop doing weird things

[SportPhish31]

All right guys I have a Palm Beach 181 whitecap cc. Its weighs around 1600 lbs, seats five and currently has a 88 johnson 140hp with a 2:1 gear ratio I think. I recently swapped the evinrude 115hp for the johnson 140hp. Its technically too much motor for the boat but its close enough for me. The whole reason I swapped was for more speed. The 140 has a 19 pitch four blade prop on it. So go lake test the boat and it runs similar speed to my 115. I was expecting more. My 115 would run around 30 mph with a 15 pitch three blade. The 140 with a 19 pitch four blade ran right at 32 mph per my gps but the motor would only turn about 4800rpm. So I threw on a spare 17 pitch three blade I had lying around and ran it at the lake and It actually ran faster. It ran around 33-35 mph. What is going on here? Notably i was a marine tech for a couple years so im fairly familiar with it all but im just looking for opinions. Shouldn't this 140 be able to turn a 19 pitch four blade? How can I get the most speed? What pitch prop should I buy?

 

[Faztbullet]

What year 115 ??? Also a 4 blade is slower than a 3 blade...

 

[SportPhish31]

95 but I think it probably has a power head from a different year. the 140 is a 88

 

[jimmbo]

Well, knowing for sure what year the engines are will be a factor in this. There were 140hp crossflows(99.6 cu. in. Rated @5000) from 1977 till 1984. In 85 a 140 looper(110 cu. in. Rated @5500) was introduced. In 88 or 89 the 140 looper had had an increase in displacement(122 cu. in.)
The 115 as a crossflow(99.6 cu. in) has been around from 1973 till well into the 90s. From 73 thru 84 it was a crank rated engine, after that the 115 was a prop rated engine. The prop rated 115hp was very similar to the crank rated 140, in fact it might just have been a decal change.
Later, in 96, I believe, there was a looper 115 added and sold long side the crossflow 115. Again two totally different engines

So if your 140 is indeed an 88 it would be considerably larger physically than a crossflow 115 or 140. Plus being either 10% or 20% more displacement would have more torque and power than a 115, or crossflow 140

Another curve to this, is the gearcases. In 1985, the 140 looper used a larger gearcase(28:13 gears) and propeller design than the crossflow 115 and 140. It was using props that prior to 1985 were for the V6 outboards and OMC 800 series I/Os. In 87 the gearcase and props returned to the sizes used on the crossflow V4s(2:1 gears in most cases)

115 crossflow rated @5000 WOT 4500 - 5500
140 crossflow rated @5000 WOT 4500 - 5500
140 looper rated @5500 WOT range 5000 - 6000

I said all that because, you may have an 84 or earlier 140, when compared to a post 84 115, will result in comparing the same engine.
Your results are consistent with the performance expected of crossflow engines

A 140 looper, especially a 122 in model would run circles around any crossflow engine

Actual model #s will determine what the years

By chance your 140 isn't an Extra Long Shaft and the 115 was just a long shaft? In addition to the extra drag, the gearcase and gear ratios are different again

 

[SportPhish31]

Well, knowing for sure what year the engines are will be a factor in this. There were 140hp crossflows(99.6 cu. in. Rated @5000) from 1977 till 1984. In 85 a 140 looper(110 cu. in. Rated @5500) was introduced. In 88 or 89 the 140 looper had had an increase in displacement(122 cu. in.)
The 115 as a crossflow(99.6 cu. in) has been around from 1973 till well into the 90s. From 73 thru 84 it was a crank rated engine, after that the 115 was a prop rated engine. The prop rated 115hp was very similar to the crank rated 140, in fact it might just have been a decal change.
Later, in 96, I believe, there was a looper 115 added and sold long side the crossflow 115. Again two totally different engines

So if your 140 is indeed an 88 it would be considerably larger physically than a crossflow 115 or 140. Plus being either 10% or 20% more displacement would have more torque and power than a 115, or crossflow 140

Another curve to this, is the gearcases. In 1985, the 140 looper used a larger gearcase(28:13 gears) and propeller design than the crossflow 115 and 140. It was using props that prior to 1985 were for the V6 outboards and OMC 800 series I/Os. In 87 the gearcase and props returned to the sizes used on the crossflow V4s(2:1 gears in most cases)

115 crossflow rated @5000 WOT 4500 - 5500
140 crossflow rated @5000 WOT 4500 - 5500
140 looper rated @5500 WOT range 5000 - 6000

I said all that because, you may have an 84 or earlier 140, when compared to a post 84 115, will result in comparing the same engine.
Your results are consistent with the performance expected of crossflow engines

A 140 looper, especially a 122 in model would run circles around any crossflow engine

Actual model #s will determine what the years

By chance your 140 isn't an Extra Long Shaft and the 115 was just a long shaft? In addition to the extra drag, the gearcase and gear ratios are different again

Thanks for all the helpful info. The 140hp model is J140TLCCM and the 115hp model is E115TXADR.
The 115hp never made sense to me because the date codes dont match up but thats what it says. No, the 115hp was a XL shaft and the 140 is a L shaft. But I have a jack plate on the boat so that doesn't play a role because I have the props set at the same level.

 

[jimmbo]

The model # for the 115 is not recognized by BRO parts search

 

[89retta]

Can you post a pic of the engine?

 

[SportPhish31]

Can you post a pic of the engine?

The 115

 

[89retta]

That 115 has the bubble back exhaust so it does have a little more power. Do you have a pic of the 140 ?

 

[SportPhish31]

That 115 has the bubble back exhaust so it does have a little more power. Do you have a pic of the 140 ?

Yeah the master omc tech I used to work under told me that its a 115 because of that exhaust

heres the 140

 

[89retta]

First off that master tech is wrong. That bubble back exhaust was found on the 140 crossflow. The 115 has a flatback exhaust. So either someone switched the exhaust or your old motor was a 140 crossflow. The 140 you have now is a looper so it should run circles around your old motor. Check compression and spark on it

 

[SportPhish31]

First off that master tech is wrong. That bubble back exhaust was found on the 140 crossflow. The 115 has a flatback exhaust. So either someone switched the exhaust or your old motor was a 140 crossflow. The 140 you have now is a looper so it should run circles around your old motor. Check compression and spark on it

Its got both, I checked it when I bought it. Compression was like 120-130 on weak battery and it hadn't been ran in a while so it could be better now. Now all I need is a prop to fit my setup. I think im going to get a stainless steel 17 pitch three blade

 

[jimmbo]

Crank rated 115s were flatback, but Prop rated 115s had the bubble back, as did the Crank rated 140s.
Your 140 is indeed a looper, and the model number does show it to be a 1988. That is good as it is the 122 inch model and doesn’t have all the problems the earlier 110 inch model, it has its own issues.
Recheck the model # of the 115, I couldn’t get anything for the # you posted earlier from BRP.

Your boat is around 18 ft. A 140 should push it around 45 - 48 mph. So either your engine is not performing, your tach and Speedo are both out to lunch, your boat has several hundred pounds of Ballast aboard or Water, hidden in the floatation foam. Another thing to check, the boat having a hook that is forcing the bow down and hindering performance

A 3 blade will help your speed. Personally I have no use for and despise 4 blade props. When I see one on boat, a cold shiver goes down my spine. But others seem to think they are fine. Typing this I gotta grab a sweater

 

[SportPhish31]

Crank rated 115s were flatback, but Prop rated 115s had the bubble back, as did the Crank rated 140s.
Your 140 is indeed a looper, and the model number does show it to be a 1988. That is good as it is the 122 inch model and doesn’t have all the problems the earlier 110 inch model, it has its own issues.
Recheck the model # of the 115, I couldn’t get anything for the # you posted earlier from BRP.

Your boat is around 18 ft. A 140 should push it around 45 - 48 mph. So either your engine is not performing, your tach and Speedo are both out to lunch, your boat has several hundred pounds of Ballast aboard or Water, hidden in the floatation foam. Another thing to check, the boat having a hook that is forcing the bow down and hindering performance

A 3 blade will help your speed. Personally I have no use for and despise 4 blade props. When I see one on boat, a cold shiver goes down my spine. But others seem to think they are fine. Typing this I gotta grab a sweater

I hope it does. It hasnt pushed my boat more than 33 mph yet but I need to get the right prop and find out.

 

[SportPhish31]

this is the model number

 

[jimmbo]

1995