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The 50 hp Tohatsu Model D2 Two Stroke
https://hpbc.ca/viewtopic.php?f=19&t=4599		 Page 1 of 1
Author:  Hounddog [ July 21st, 2024, 11:56 am ]
Post subject:  The 50 hp Tohatsu Model D2 Two Stroke
This is the dyno test results comparing a race prepared top 3 finisher Mercury 44XS to an out of the box non race prepared 50D2 Tohatsu
The HP is at the crank shaft
RPM M....... T
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 .......impressive for a fishing motor
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 53.3
7200 52.1 50.1
7300 51.1 48.4

The 50D2 is one of the last Two Stroke models in UIM.
3 versions...a Mercury, a Mariner and a Tohatsu.....all the same motor.
https://www.uim.sport/Documents/Homolog ... y_50D2.pdf
Author:  Hounddog [ July 22nd, 2024, 3:35 pm ]
Post subject:  Re: The 50 hp Tohatsu Model D2 Two Stroke
Do I know similar information about the OMC 60 hp twin??

The powerhead specifications for SST 45 are posted on the APBA site. Years ago UIM did have the specifications on their site when the short shaft version raced in S750.
There are different casting years for the engine blocks. They talk about big “100” stamped blocks and single bolt lift ring blocks as being better.
The "experts" will tell you that you NEED a 326100, and that a "big numbers" 326100 is better. If you're into mod stuff, just get some new sleaves, straight rods, and a good crank then go to town.
I hear that blueprinting the replacement sleave ports and making them look like factory original is the easy way to get a good motor. Those "amazingly close to spec" motors motors seem to be break a lot though... or maybe it's just coincidence?
We have had several of these motors race in T750. The motors really benefited performance wise if they were rebuilt to spec following the spec sheets.
A few racers in SST 45 in the states did expensive builds that included special crankshafts and extensive machine work.
The racers here in T750 mentioned that it wasn’t difficult to improve the performance with any of their powerheads, but it was definitely difficult to get one that was significantly better than the rest.
Based on what I was told.......65-67 hp is common after a spec rebuild.
..........................................68-69 hp is a real good one
..........................................70-72 hp was possible with the special parts and machining
Those numbers are based on a powerhead that will pass inspection at an APBA national event.

There is at least one engine builder in the states that built a modified motor...his motors have expansion chamber exhaust and custom parts.
https://www.facebook.com/groups/1990783 ... 149865311/

Others have far more knowledge about these motors than I do....it would be good to here from them.
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