if this is what you are asking...

1" of pitch will load up your motor a lot more than 1" of length...

Sorry I wasnt clearer, Im talking about getting a load up and going on plane, inch of pitch or inch of diameter? I know the 11inch would push more per rotation, but how does that go vs the 12.25 diameter being able to grab more water, just trying to get a grasp on the physics here.

I guess I had made some assumptions so level set some information-

What was done to the motor by EVT? Since you mentioned Rev limiter and head trouble so I assumed M-carb and heads, correct? Anything else?

Also- when you baselined the motor at 19hrs when you got it- was it summer time? Temp and humidity have an affect on performance, lower temps and low humidity can have considerable performance gains. The Briggs manual will even tell you that you loose 10% for every 10 degrees over 72 degrees (if I remember right). As stated above, hooks in the hull will also affect performance from that original baseline. Your gears have teeth and there is no 'belt slippage' in your setup. As stated above, if your bearings were rusted up you would feel it in the housing when you turned the prop by hand (either rear or forward bearing set) or you would hear a whine or squeal when running. There would be noticeable symptoms if it was robbing alot of performance.

The stock motor was designed for the smaller prop (i.e. the stock gear ratio matched with the stock engine/RPM) but I assume you have added power to the motor and it seems from your numbers you are able to turn the BB prop. The larger blade face of the prop will provide you better hole shot and load carrying over the smaller prop size if you are able to turn it with the load you are wanting to carry (which in my opinion- 4 guys is too much for a 15' boat but we will leave that for now). Note: adding cup to a MB prop will kill performance, save yourself the time and expense.

Your motor is delivering max torque at a specific RPM. The lower unit you have allows changing the gear ratio to fine tune your performance. Adjusting the gear ratio allows you to add more load to the motor to fine tune your RPM to run in the target performance range. Going with a lower gear will spin the prop faster at the same RPM. You can achieve similar tweaking by adjusting the pitch of the prop but: a) its more expensive b) its less accurate and many times not as repeatable from wheel to wheel. The worn wheel you have that has lost 3/4" is trash- it will give you alot of RPM due to the reduced size but the cup is certainly gone from it.

You need to eliminate variables- decide which prop you want to run and do you want to tune it for max load, light load, or mid-range. The motor mods are now a constant so then you can either run it as is or adjust gear ratio to fine tune the performance. Note- planing out 4 guys with a 23 in a 15' boat and running the numbers you are running is really good. Putting a smaller lower gear in will add more load to the motor but will spin the target prop at a specific RPM range that gives you the most power- you may reach a point where even though it will spin faster, you get no performance gain from it. On the hole shot, you can go too far down in gear ratio and load it down so much that it will kill your hole shot.

Hope that helps.

DB,

Earlier you said "Take your gear down 2 teeth (if its a 50 lower gear, go to a 48) which on a 35 with 38 top an 50 bottom "

So. assuming you still reccommend this change, it will drop engine rpm
and increase prop rpm..... Thus adding a bit of speed - but reducing
lo-speed power a bit....

So gearing down is just getting your engine spinning in your ideal powerband. What is the traditionally thought powerband on these small block briggs? Id be worried to go too low and bog down.

For now Im sticking with the big blade, trying to resell the 11x10. Has less than 30min on it, got it in the classifieds. Asking 200 TYD, took 250 to get it shipped here, trying to get a little money back. Let me know if anybodies interested.

I ran a 34 upper and 50 lower on my 23 Hyper Balanced, with shaved heads along with a rev-kit and a Hopkins prop that closely resembles the 2 blade GD prop. Had decent performance on a 1748 BT hull.