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1989 Johnson 150 crossflow
1986? Charger DL 18
4" manual jack plate
Cavitation plate even - 3/8" above pad.
So, I've had a chance to put about 8 hrs on the boat since it's been put together. I have several props for this boat. I can't get it to rev up to the 5500RPM @ wot.
Props I've tried:
14.25 x 23" 3 blade Ballistic turn 4700rpm. Other than the RPMs this props really works nice. Great holeshot and lots grip and lift.
14.25 x 21? SST2 double cup run 5-5100 this prop is supposed to be 23" pitch according to the part number but it has a 1 stamped over the 3 in 23. Don't know the history and neither does the guy who sold it to me. So far this is the fastest prop @ 57mph (gauge) lots o trim
14.25 x 21 aluminum. Blah. 49-5000 RPM but slow. 48ish mph
I also have but haven't tried
Laser II 13.5 x 24"
SST 14x 25
Precision turbo 14.25 x 26
I can get a few more revs sometimes with some trim but the boat starts to pourpos.
I shouldn't have to go down to 19" to get my revs up. I don't wanna be the guy with the little prop. Good holeshots with all props I've tried. I have a new Teleflex Sterling tach in the boat set to 6P and really no other way of verifying the RPMs. It doesn't sound like it's turning more than 5k.
Here's the thing. My Dad's got a 1979 Johnson 140 V4(all original)on a Sidewinder Super 16 that will spin a 13.25 x 23 SST prop 6000 rpm all day. It's a dog out of the hole but... Now, you can hear it's screaming. We also don't make a habit of it but it will go there.
So, what's up with the 150?
I've got to keep the old man behind me. I can't have a bigger motor and go slower.
That Sidewinder kicks the shit outta our neighbours Charger SK 18 XR6 150.

Any thoughts?

I'm thinking your motor is really low and that's dragging the revs/speed down. I don't really know my johnnyrude specs so I'm not sure what ratio is in the lower to compare to others setups.

It's supposed to run 5500RPM @ WOT
As far as I know the drive ratio is 1.86:1
93 Octane
Bypassed the VRO, running premixed 50:1 AMSOIL Marine HP
No low water pick up

What about engine temp? It runs stone cold as far as the pisser indicates. I'm sure I need thermostats. It would warm up the pisser in the fall when I had it running on the stand. Now the piss is cold. I'm sure this will have an effect as well.

Do you have a temp gauge? I'd try get the motor up higher and try that sst2 prop again, like dok said your motor is quite low.

I have a temp gauge and sender. I'm in the process of wiring it up. I'm going to move the sender to the top/highest cylinder head.
I just finished ordering a water pump kit, thermostat kits and pressure relief valves, seals and springs.

About engine height; how high can I go? 4'' setback with a Powerlift manual plate. Crank it up until I loose water pressure and back it down some?
Sounds like Newphie tire pressure, pump it up 'til it goes bang then let out 5lbs. Also about height; I am running Raker style props not cleavers or choppers. Can a Raker be run to pierce the surface?

If I have a straight edge on the pad can it cross just above the top water intake hole? I'm positive I won't get this thing to prop walk but it would be nice to have it run like it should. I think a 150 Johnny should be able to spin a 23'' prop. You see people running big props all the time.

Id start with going up 1/2" to an inch. I ran laser's on my 75 mariner, it was up pretty high and it ran great. I was never running it like you would a cleaver but it should work until you get that motor way up compared to now.

I'm not in exactly the same position you are talking about here, but after a season of running since I got the boat, I went through a pretty thorough engine diagnostics this spring on my 225 Johnny.

We checked compression and leak-down, Fuel flow, tore apart the carbs and cleaned, synced the carbs.
Turned out, I had a bad VRO/Fuel pump. It was leaking fuel back through the vacuum. We ended up going with pre-mix, a Carter fuel pump, regulator and pressure gauge.
After all the tweaking She's runnin like a top. Edling is better, top end RPM and speed is better as well. We might even be seeing better fuel and oil consumption, as the plugs were black and wet most of last year. Running rich. Now they are the nice brown colour and dry.

My guess on this problem is fuel related.
Your plugs are a possible indicator of what is happening. Black and wet = to much fuel and that will cut your performance. Light brown and it's too lean, that will also effect performance.

I'm a long way from an expert, but check that out and see what's happening.
Also a compression and leakdown will help to incicate the condition of the cylinders, rings etc.

Good luck!

Update:
Still haven't hit the "screaming" limit of 5500rpm.
Jacked the engine up to where the cav plate was about 2-2.5" above the pad.
Ran 62mph at 5100rpm with the 25 SST
Ran about 58-59mph at 4900rpm with the Precision Turbo 26
Now:
The Turbo carries the boat really well. Lots of lift and good traction. I can trim it up all day long.
The SST runs faster but I can only trim it so high and then it blows out. Like half as much as any other prop (SST II, Ballistic, P. Turbo). I LOWERED the engine height to get the prop to bite better and give me more trim. One step forward and back.

Stock lower unit, no LWP. 4" setback
Should I run it as high as the prop shaft 2" below the pad?
Should I be measuring the Cav plate to the bottom of the pad or prop shaft to the bottom of the pad?
I have a long way to go up before I max out my jackplate.

So here's another thing; even when the prop blows out and slips the engine STILL won't hit 5500rpm.
WTF?
I'm going to do a plug check but I'm sure they are fine.
I think that the timing is not advancing either properly or far enough. I need to take apart my control box and insure everything it tight and tensioned correctly.

Any thoughts?