The data is in

I finally got my 96 176 on the water after a long rebuild process.
Stock Crank and rods with Forged pistons.
Custom grind cam with .550 lift, 227/224 duration, 112 lobe centers
Roller lifters and rockers
185cc heads with 58cc chamber 2.02In/1.60ex valves
Edelbrock RPM intake manifold
Quick Fuel 750 cfm with mechanical secondaries
Redline Aluminum Exhaust manifolds

At 5000’ with an Acme 422, up to about 3200rpm it was 1MPH/100 rpm, then the speed fell off a little in relation to rpm’s. Top speed was 51mph @5600rpm.

I don’t know what it all means but it was fun to listen to it sing. I hooked up an AEM 02 sensor. It was running a little rich at 10.9-11.3, at 5600rpm it leaned out to 13.5.

Wow, that's fantastic. I bet it sounds amazing @ 5,000+ rpm.

Is there still a muffler inline somewhere? Or is it just straight to the transom?

Hate to disagree with joe but I suspect the nature of the diminishing returns st higher speeds has a lot to do with the planted nature of the NWZ based hull (even moreso than the 2001). I’ve seen 1:1 tracking (speed vs rpm) up to about 40 and then a 500+ rpm differential at wot, even when topping out in the mid 40’s. All with perfectly tuned props. The faster you go, the smaller the speed returns for a given (additional) RPM.

I also haven’t seen advantages of larger diameter props from a speed perspective... once you get into the 12.5” diameter range on these size boats, they all seem to push ok. Holeshot probably improves notionally with larger diam, though. There is a new Acme 3-blade option in the 13x16 range that would be fun to try if getting the revs down would be advantageous... all depends where that engine is making peak power. Those are good numbers for that hull at 5k’. Curious what type of “185cc” heads they are.

TRBenj wrote: Hate to disagree with joe but I suspect the nature of the diminishing returns st higher speeds has a lot to do with the planted nature of the NWZ based hull (even moreso than the 2001). I’ve seen 1:1 tracking (speed vs rpm) up to about 40 and then a 500+ rpm differential at wot, even when topping out in the mid 40’s. All with perfectly tuned props. The faster you go, the smaller the speed returns for a given (additional) RPM. .

There is all that 2 but I have seen 4-5 mph change on the same boat with the same prop at the same rpm just before and after being reconditioned (by acme)... no difference in performance upto about 50mph - only explanation that works for me on that case is that the prop is not holding shape as well as it did before they sanded off the lines or that they aren't getting the shape back perfect... but the latter explanation doesnt explain why the track the same until higher rpm. .   What is known for sure is that it slips a whole lot more at 53mph than 57mph if they both occur at the same rpm.

Yes the nose planting and general prop angle at high speeds causes the increased drag that is what is making the prop slip more at the higher speeds but if the engine can still increase rpm greater than its peak hp then you need to address that increasing rate of slippage if you want to go faster.    It's the same reason you need more prop diameter or more props and not just more power to pull more skiers - if you cant use all your hp what good is it.

We can't really add another prop here, so to address slip you are limited to a few options. For the same material/thickness/profile/rake - props will slip less with more diameter, more blades (to a point), and more pitch -

More diameter gives you a bigger water column to push and will slip less for a given rpm and speed.   Now it takes more energy to turn it through the water to begin with so maybe you cant get to the same rpm you could with a smaller diameter but either way you are better utilizing the hp available.   Obviously you are going to reach a limit here quick but there are big changes in prop area to be had when you increase the diameter even .5-1"

Props with more pitch hold their shape better under load, but also require more torque to turn through the water at a given rpm - so more is better until its too much and then its not good at all - but if you feel your peak hp is at less than 5700 rpm and diameter increases failed to get you there then a little pitch might be a win/win.
4 Blades is what you have now, so you are not going up there. I think less blades on a prop that is already being taken to the point where its rate of slippage is going up fast is probably not a top speed winner, although generally more efficient.   If the boat was lighter or easier to move through the water then a 3 blade would likely be an improvement, but I think that's how you get a 48 mph flat bottom ski boat to 49.7 not how you get a 51-52mph boat to 54-55.     

For the same material/thickness/profile/rake props will slip less with more diameter, more blades (to a point), more pitch -

Obviously I dont have the experience/smarts to comment on any of that, but I am enough of a geek that many years ago I put this spreadsheet together to play with prop slip, if anyone is interested and wants to play with it. Also, may not be right, if anyone finds a fault in my logic, let me know.