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TBroccoli
06-16-2015, 08:11 AM
Happy to say the 1996 22 classic is still pretty quick. I have to admit I've only done routine maintenance on her over the past several years.

But ---- this weekend she showed how well she still moves. Saturday evening on a hot calm night with 3 aboard and a full tank of gas she ran just shy of 67mph. But then on Sunday, with slightly less gas, hotter then hell, calm, with 6 aboard and a dog she ran just shy of 63mph.

This boat is amazing. Solid as a rock. 100% stock: 454Mag, bravo 1.

Still happy to be a donzi owner.

undertaker
06-16-2015, 08:17 AM
T you still running the Sassafras River? Do not get down as much to that area like I did in the past...


Undertaker

TBroccoli
06-16-2015, 11:29 AM
Yes. We almost always hang out at buoy #10. Ordinary point has been covered with a rock sea wall.

Pismo
06-16-2015, 12:54 PM
You are going faster, your speedo is off. For a non-Mag that would be good but you are faster.

TBroccoli
06-16-2015, 01:38 PM
Pismo, You think I am actually going faster then 67mph (loaded)and 62mph (overloaded)?

I hope you're right. I will calibrate speedo again with my handheld gps.

Thanks

Pismo
06-17-2015, 08:20 AM
Pismo, You think I am actually going faster then 67mph (loaded)and 62mph (overloaded)?

I hope you're right. I will calibrate speedo again with my handheld gps.

Thanks

Yes, should hit low 70s with lots of trim. What prop? My 1996 22 with a 502Mag MPI, only 30 more hp, has hit 75.5mph(many times) GPS with a labbed 27" Mirage Plus, and 74.5 GPS with a stock 25" Mirage Plus prop. Trim is the key, more than you think.

TBroccoli
06-17-2015, 12:07 PM
I've got a Mirage Plus 23. Trimmed out, at about 4800 - 5000 rpms.

gotta find a Mirage plus 25 to test.

Ghost
06-17-2015, 12:43 PM
Unless I'm missing something, from the sound of it, your Mirage+ 23 is just right since your RPMs top out at 4800-5000 (tel:4800-5000). The 25 should knock down your RPM by 400-500 RPM.

IF the HP the motor produced was the same with both props and other things were equal, WOT speed would be the same with both props, and the 25 would top out from 4400-4600 RPM. But since peak power for the motor is probably up near 5000 RPM, you won't reach peak power with the 25. As such, I expect you will lose slightly more than 400 RPM, lose a few HP, and lose a little speed.

TBroccoli
06-17-2015, 12:47 PM
Is it possible that the motor could turn the 25 mirage plus at the same rpm as the 23 MP? Then the speed should increase???

Just Say N20
06-17-2015, 01:47 PM
If that were to happen, with both props running to the same max rpm, that would suggest something was out of whack with one, or both of the props. Or there is a rev limiter at work.

The amount of pitch is what determines the load on the engine. An actual 23" pitch prop loads the engine less than an actual 25" prop. Less load would allow the engine to spin faster, unless there is an arbitrary rpm limit, set by a rev limiter for example.

If the distributor has a limit set (the MSD in my 16 engine did, and you could set it to whatever you wanted), that would make the engine top out at the same rpms if it was strong enough to spin the 25" prop to that limit. If this were the case, then yes, it is possible to spin the engine to the same rpms and go faster. However, this isn't representing the true top speed of the boat.

Ghost
06-17-2015, 09:04 PM
What N2O said.

Further, I would add that what is needed to push a boat at a given speed is POWER. Not torque, or RPM, or energy, etc. A certain amount of power is needed, period. The motor will produce different amounts of power at different RPM. If you are getting the max power from the motor without some unusual problem with loss due to inefficiency, you're pretty well topped out. Switching to a different pitch of the same sort of prop is only going to shift you to an RPM level that is no longer at the peak power for the motor.

Now, if you were running a 4 or 5-blade prop and switched to a 3-blade, the DRAG might decrease and thus the existing power might then push the boat faster. And you might be able to turn more pitch at the same RPM. But switching pitches within the same flavor of prop is mostly just changing gears. And those Mirage props are usually the fastest, or close, for the sorts of boats at the speeds where you are.