NEED PROP ADVICE: '78 Johnson115 2stroke/ '82 Ranger 330V

[phx5kegsman]

Hello,
I want to upgrade to a stainless prop. Currently running a stock aluminum 13 x 19. Hole shot is decent, but I suspect that might be from the hydrofoil (on it when I bought it). I run 42mph at 5200 rpm, with a little bit of throttle left to hit WOT. Not sure what my max rpm's are. I'm looking to get better performance and speed. Any suggestions?
Thanks!

 

[airshot]

My suggestion is to get all the facts in order, or your just guessing. Need that max rpm at wot and also what is the max wot rpm rating on the motor !
Be careful with that fin, while they can help, they are also known to break cav plates on out boards when in excess of 40 mph. How much are you willing to gamble for a couple more mph ??

 

[jimmbo]

4500-5500rpm is the WOT Range
As mentioned Above, 42mph at 5200 with a bit more Throttle is Meaningless. You/we Need to know what it actually is at WOT.
Is the motor in good Mechanical Shape? Compression numbers, please
Is the Spark properly advance at WOT?
Are the Carbs fully open at WOT?
Is the Engine mounted on the Transom at the Correct Height?
Is the engine Properly trimmed at WOT?

Myself I would remove the Hydrofoil and see how far from the boat I could throw it.

As for the Stainless, unless you are choosing a Stainless Prop that is designed as a Performance Prop, instead of just an SS version of an AL Prop, you aren't going to see any significant changes in Speed. Be aware that any Impact when running a SS, can result in more Damage to the Drive Train than with an AL Prop.

 

[cyclops222]

GPS mph ? Is the tachometer accurate when compared to a accurate one ?
How did the person who installed it KNOW where to mount it for a loaded boat ?
WOT what happens to the bow angle. As you trim the motor ? ?

 

[airshot]

4500-5500rpm is the WOT Range
As mentioned Above, 42mph at 5200 with a bit more Throttle is Meaningless. You/we Need to know what it actually is at WOT.
Is the motor in good Mechanical Shape? Compression numbers, please
Is the Spark properly advance at WOT?
Are the Carbs fully open at WOT?
Is the Engine mounted on the Transom at the Correct Height?
Is the engine Properly trimmed at WOT?

Myself I would remove the Hydrofoil a

4500-5500rpm is the WOT Range
As mentioned Above, 42mph at 5200 with a bit more Throttle is Meaningless. You/we Need to know what it actually is at WOT.
Is the motor in good Mechanical Shape? Compression numbers, please
Is the Spark properly advance at WOT?
Are the Carbs fully open at WOT?
Is the Engine mounted on the Transom at the Correct Height?
Is the engine Properly trimmed at WOT?

Myself I would remove the Hydrofoil and see how far from the boat I could throw it.

As for the Stainless, unless you are choosing a Stainless Prop that is designed as a Performance Prop, instead of just an SS version of an AL Prop, you aren't going to see any significant changes in Speed. Be aware that any Impact when running a SS, can result in more Damage to the Drive Train than with an AL Prop.

A " hydro frisbie". Wish I would have thought if that !

 

[phx5kegsman]

I'm sorry for disappearing from this thread, but life threw me a curveball that I didn't see coming.
In response to JIMMBO's comments:
1. Yes, the motor is in good mechanical shape. All cylinders between 102-110psi (on a good gauge)
2. Since I have owned this motor I have replaced ALL of the ignition components, and set everything exactly as the factory service manual specified
3. Carbs have been rebuilt and link n sink done according to manual. I believe they are opening, but haven't actually looked.
4. When I bought the boat(82 Ranger 330V), the motor was mounted all the way down on the transom. Two years ago I moved the motor up from the transom to the next adjustment hole. I'm not sure what the proper height should be but I felt that the motor sat to low in the water, especially when I had a full fuel tank. The tank is, unfortunately, mounted all the way to the back of the stern. Later model years have tanks mounted beneath the seats. I'm sure that makes for better load distribution.
5. The motor is trimmed all the way down at WOT
Also, I did remove the hydrofoil fins. I'm not sure if that had anything to do with it or not, but I topped out at 45mph last time out

 

[jimmbo]

4. When I bought the boat(82 Ranger 330V), the motor was mounted all the way down on the transom. Two years ago I moved the motor up from the transom to the next adjustment hole. I'm not sure what the proper height should be but I felt that the motor sat to low in the water, especially when I had a full fuel tank. The tank is, unfortunately, mounted all the way to the back of the stern. Later model years have tanks mounted beneath the seats. I'm sure that makes for better load distribution.
5. The motor is trimmed all the way down at WOT
Also, I did remove the hydrofoil fins. I'm not sure if that had anything to do with it or not, but I topped out at 45mph last time out

#4

#5
Trimmed all the way Down at WOT? That is one way to really kill Top Speed, and create a very Dangerous Control Situation.
Trimming all the way Down is done to reduce Bow Lift getting on Plane and running at very low Planing Speeds. Usually once on Plane, the engine is Trimmed out, until Porposing happens, then trimmed back in/down until it ceases. As speed goes up, the Engine can often be trimmed further out

 

[phx5kegsman]

In response to CYCLOPS222:
the speed was measured on my Garmin because the GPS speedo that I installed stopped working. I am also skeptical about my tach because I've seen the needle "bounce" up 5k rpm and then slowly go back down. I heard no change in the engine. I rewired the entire boat. It could be my wiring or could be crappy gauges.
From a dead stop, with the motor trimmed all the way down, I go full throttle. The boat gets up on plane quickly and I back off on the throttle to avoid porposing. My bow angle is level the whole time. There's been a few times that I thought the bow angle was slightly towards the water! Am I doing it correctly? Should I be using the trim more? I don't usually touch it except for turning

 

[jimmbo]

Do you have Power Trim, or just Power Tilt? Both were offered in 78. There is a Difference.

 

[racerone]

Well---102 PSI compression would indicate that there are issues with the motor.

 

[jimmbo]

Could be a Gauge Issue too

 

[racerone]

He states it is a " good "gauge.----Here a motor like that would have the cylinder head off in a heartbeat !