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The comparison was done several years ago. Bass had built custom midsections and gearcases for the tohatsu 50D2 model so it could race in Stock Outboard “D” class. The test is very interesting for a few reasons.....the Mercury 44XS was a race prep top running motor. The dyno numbers show the great improvement and why racing prep makes a difference. The Tohatsu is not race prep. It is bone stock just as it was shipped. You wonder how much better it would be when it was race prep.
Both these motors are a production outboard. The racing outboards like Yamato develop their maximum horsepower at higher Rpm...example 33 hp @ 6600 rpm. That’s the reason they perform so well on raceboats.

CBHP = Corrected Brake Horse Power.
RPM. Merc 44xs tohatsu 50D2
3500 ........27.5 .....................34.6
4000........ 33.8 .....................40.8
4500 ........40.4 .....................45.3
5000........ 45.9 .....................47.8
5500........ 49.5 .....................51.3
5750 ........51.3 .....................55.3
6000........ 52.5 .....................56.2
6100........ 53.1 .....................56.2
6200 ........53.5 .....................56.5
6300........ 53.8 .....................57.0
6400 ........54.0 .....................57.2
6500 ........54.4 .....................57.8
6600........ 54.3 .....................57.0
6700........ 54.7 .....................56.1
6800 ........54.5 .....................55.5
6900 ........54.6 .....................55.1
7000......... 54.3 ....................54.4
7100 .........53.7 ....................53 39.
7200 .........52.1 ....................50.1
7300 .........51.1 ....................48.4

Remember these are horsepower at the crank shaft. A production outboard is rated at horsepower at the prop shaft. Both these powerheads as production models would be advertised as 50 hp at the prop shaft . Even at 7000 rpm these stock ported motors make good horsepower. You can see how the race prep mercury performs better at the higher rpm.

First fact......the 50 mercury was advertised as 50 hp at the prop shaft. That wasn’t accurate. Based on the numbers the motor even with race prep wasn’t 50 hp at the prop shaft when you consider the difference between crank shaft horsepower and prop shaft horsepower is approximately 4 to 5 horsepower less.
Where as the tohatsu is 50 hp.
5500........ 49.5 .....................51.3
5750 ........51.3 .....................55.3
6000........ 52.5 .....................56.2

The 70-65-60 hp mercury triples were also overrated. That’s the reason the twin carb 49 cubic inch twin carb mercury triples can race in T750.

You find the opposite case with the OMC 45 cubic inch twins , the 49 cubic inch triples and the 56 cubic inch triples. They are a bit under rated. A race prep 45 cubic inch OMC twin makes far more horsepower than the 44 cubic inch mercury and and bit more horsepower that the mercury 49 cubic inch twin carb triple.