Detroit 671ti's proper propping?

What do they consume at WOT or max HP? What is your hi idle (max rpm no load) and max loaded rpm?

Ships total fuel use at 15 kts; 23 GPH; 230 HP total; 115 HP per engine. Just over 1.5 gallon per mile.
What RPM is that, 16-1800?

In my years of purchasing old twin engine inboards, I've always got stuck with the old props that were rebuild so many times, the diameter was way gone. One boat, the previous owner even reduced his pitch because of the stuff he had on board (junk), removed it and the boat was under pitched.
At 1900 to 2000 you should be making some HP and burning near 23 GPH per engine, also boat speed should be up also.
You have the 380 hp beast?

My 6-71s burn 16 gph aside turning 1950rpm , pushing 44K lbs. to 19knts
J&T 'd to 450hp each.

I think you are way under propped.

That changes things.
Any particular reason why you detuned them? Ralph might have insight but I suspect you may be having to adjust these props after checking WOT this weekend.

Now I'm coming down there to beat you with some old & stale noodles.
If you didn't want to stress them, keep the throttles back. Now you have a non factory config vs your serial number.
So, Back to it after your lashings; That's 410HP at the flywheel, 380 at the prop. You lost 70HP off the top. I'm familiar with the tune as long as the timing height is correct. But you may still be under propped. What diameter wheels do you have? Pitch? Reduction?

Boomer..the problem is that in time you won't be happy with the speed so you're going to push them past 2000 rpm and now you're going beyond 80% which isn't good for them.

Pretty tall on the stb but o k for now.
Next go for a WOT run, We want to see no more than 2450 mid loaded boat.
2400 fully loaded.

Don't forget the bait. As long as your off da dock!!!!!

I would be concerned with that "tall number".

The Fuel Rack on the Governors for the 6-71 Detroit's would be set at 200rpm over rated rpm, so a No load Idle rpm would be set at a max of 2500 + 200 = 2700rpm for your engines.

A 3062rpm at No Load would flag an issue or two:
1. The Fuel Rack needs to be reset
2. The Gauges may not be reading/operating correctly.

3000+ rpm and you are testing bearings and connecting rods, if in fact the gauge was accurate . Sample specs for the 450hp version of the 6-71TI below:

I agree with Pacblue. Buy a photo tach and put the reflective tape on the harmonic balancers and have someone shoot them at WOT and know exactly what your rpms are.