Need advise on RPMs shooting up like 500RPMs w/ new engine

Update:these series of shake down where done w/ same not perfect 14.25x19 prop.



engine lowered at rest made a significant improvement in performance image

previous height the round piece on gear case wasn't halfway submerged like it is now.



during these runs the max RPM at WOT was kindof steady at 5500RPM but did creep up toward 5800RPM on the later 4th an 5th runs.



I have a almost perfect Viper 14.25X22 stainless steel. How much would this lower RPM at WOT? I have been informed by baeckmo the desired RPM is 5200 not sure if this applies to my 2012 model?



Additionally I did a couple long turns at speed an the prop tips seamed to stay planted in the water.

Shakedown w/ a little trim

https://youtu.be/r5KdyEKMXm4





barely see cav plate

https://youtu.be/-fAPqW5I83g


2nd #1 shakedown of tack which seam to be functioning normal at wot

https://youtube.com/shorts/5MNviPfU5Tw


vessel didn’t seam to get on plane instantly like w/ previous carbed 175hp engine it kindof felt like the prop was losing traction around 3500 but seamed to motor on to WOT.


I don’t remember all the turbulent water being kicked up around the engine. However the new live well pump needs to be shortened also I neglected to tighten the pods drain plug so it was hanging down a tad over 1”.


I feel the engine is now mounted at an acceptable height maybe all she needs is a decent prop. To get the get traction during holeshot an mid RPMs. Thanks for advising

 

It's about 150-200 rpms per inch of increased pitch. But going to SS and a change in cup will make those estimates less accurate.

 

I think the pitch is correct at 19 w/ WOT at 5500 w/ engine tucked. then when I trim up a tad RPMs slitely increase maybe 200RPM. it's hard to tell bc of the wind noise interfering w/ the recording plus I have two types of videos engine then tack.
next shakedown I mite connect the GPS an monitor speed an tack my new Ray marine has a split screen which w/ a added sensor to the ETEC
will also display trim this way I can monitor tack/MPH an trim. setting up the new Ray is low priority right now.

since I'm close in desired RPMs w/ the 19 testing the 14.25x22 would lower the RPMs conservatively 500RPMs maybe less trimmed up.
so probaly not worth the effort. I'm leaning toward a new 14.25x19. I think the slitely dinged 19 is creating cavitation an it's not losing traction due to ventilation. will report back an thanks for advise.

 

How much speed increase ? If you compare to normal setup ?

 

According to my google WOT RPM for a 2012 Evinrude 175hp G1 is 4850 to 5850. For boats that could have a heavy load at times, you want to be on the high end of the RPM range when testing with a lighter load.

 

I don't use joogle much I use Duck Duck. 4850 sounds way low I'm assuming this is for folks w/ low pitch that prioritize hole shot over speed.
me personally prefer both whole shot an speed.
you make a valid point about being on the higher RPM side during testing w/ the lighter load which I am thanw/ a more loaded vessel.

this is a recreation vessel besides additionale full load of fuel 40 gallons 290LBs an maybe a extra loaded cooler weight will only increase say 200LBs (or less for additional passenger) the gear weight will remain constant. so add around 500LB for full load condition. while I'm testing w/out this extra weight.
the current Michigan wheel inexpensive aluminum prop. 14.5x19 has the WOT RPMs steady at 5500. again this prop isn't prefect it has a few imperfections basically a spare prop. additionally this prop. has minimal cupping.

my new aluminum prop. made by Johnson/Evinrude OMC PN 391201 14.5x19 has twice the cupping that extends the lenght of the fins. so I'm hoping for more stern lift which results in quicker whole shot while the same 19" pitch maintains the 5500 RPMs.
should receive new prop. middle of next week. thanks willy13 for advise.will report back w/ better videos on next shakedown runs.

Montero "How much speed increase ? If you compare to normal setup ?" I can't say what the increase of speed is from the orginal engine was a inboard w/ stern drive which I've never used. remember I did the inboard to outboard conversion. I can mention orginal vessels go around mid 30MPH where w/ the modern ETEC I'm in upper 40s.

 

I’ve ordered another prop. A brand new OMC Viper14.75X19 stainless steel.



hub has some corrosion maybe a wire wheel can clean it?
I believe the smaller piece sits in front of the prop. an since my engine had a Viper this smaller piece is already there?

Found this infor. in bold on the net. from searching will Stainless steel reduce or increase RPMs compared to aluminum of same pitch size?
Stainless Steel

+200 RPM (approx.)
Generally runs faster than aluminum of the same pitch.


next search about increased diameter reducing RPMs.
Yes, increasing the propeller diameter by half an inch can reduce RPMs, typically by about 500 RPMs for each inch of diameter change. Therefore, a half-inch increase may lead to a decrease of approximately 250 RPMs
Engine Load: A larger diameter propeller provides more thrust but also increases drag, which can affect engine performance

So in theory going from the aluminum 14.5X19 to a stainless steel 14.75X19 I gain 200RPM just in material change. Currently w/ aluminum at 5500RPMs so add 200 5700RPMs. secondarly the increase of ¼” in diameter reduces the RPM by 125 so mathematically the new viper SS should net produce 5575RPMs.

The new Viper has a decent amount of cupping not sure how to factor cupping into this equation.
What I’m hoping for is more stern lift resulting in better holeshot.top speed is preferred over cruising effiency bc I have 40 gallons of saddle tanks an two reserve six gallon, total 52gallons capisity plenty of fuel for a three day cruise w/ the effienct ETEC.

Planning next shakedowns w/ newer aluminum this week. Will receive brand new Viper end of next week. Thanks Guys for advise

 

You will lose RPM going from aluminum to stainless while keeping all else constant. Stainless will flex less...