Baja 16ss prop recommendation

[Muc]

I got this hull from a buddy who had it sitting in his garage for 10 years. It came with a 150 merc and a 140 evinrude both 1984 engines. He had never had an engine on the boat, so I have no baseline.
Hull is balsa core with no stringers, just a couple of knees at the transom. Transom and hull seem strong with no rot that I can find.
I put the 140 on with a jackplate and a 12 3/4" X 21p aluminum prop.
After playing around with engine height, I have some questions.
I'm using a extra speedometer as an water pressure gauge and I'm unable to get the engine high enough to lose water pressure. When I raise the engine too high I start ventilating as I come up on plane. Is this normal that I can't get the engine high enough to lose water pressure?
When I have the engine at what seems to be the best height for top speed. I'm getting 53 mph at 6000 rpm as my top speed. I'm not 100% sure on these numbers because they are from the boat speedo and tach. I have a GPS on order and hope to get a buddy to drive the boat while I use a shop tach to confirm.
I think this motor is only supposed to turn 5500 rpm. So I'm guessing there is no rev limiter in these power packs.
Should I try to find a S.S. 23p chopper to try next? Or go up to a 25p?

[David]

I used to have a 16 Baja with first a 100 cross flow and then a 115 HO. 4” manual plate. Around 3” below the pad worked best. It was not sensitive to height with the 100. Plus or minus an inch was hardly noticeable.

The 115 HO would be heavier and about as powerful as your 140. 64 on the rev limiter with a 23 SRX or a 24 Raker. 66-67 with a 26 small ear chopper and a 27 Hoss copy. Only the small ear chopper cavitated coming onto a plane.

[Muc]

David, Thanks for sharing your experiences. When you say 3” below the pad. Are you measuring at the prop shaft? I have been measuring to the ventilation plate. Seems like it would make more sense to use the prop shaft as the reference.

I’ve been talking with a local prop shop and they don’t have anything other then cleavers in stock. But did tell me they have a good customer that plays around with the old inline Mercs and that they might be able to get something from him.

It sounds like something around 25p might be a good next step.

I’ve spent the last 30 years with I/Os and I’m finding that being able the change prop shaft height means that this is going to be a real learning experience.

[David]

Prop shaft about 3” below pad