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What’s Happening With The 70CES Yamaha?
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Author:  LittleCharger [ January 22nd, 2024, 10:38 am ]
Post subject:  Re: What’s Happening With The 70CES Yamaha?
Roflhat wrote:
But he had a lot of tricks up his sleeve too, small clever things which are probably all worth less than 1% each but add up.


agreed they do add up !
Author:  mattmak [ January 22nd, 2024, 6:27 pm ]
Post subject:  Re: What’s Happening With The 70CES Yamaha?
LittleCharger wrote:
agreed they do add up !


:roll: :? :(
Author:  Hounddog [ February 7th, 2024, 11:40 am ]
Post subject:  Re: What’s Happening With The 70CES Yamaha?
There were many SLT drivers running different outboards.....tohatsu 50 hp.....Yamaha 70 hp....OMC SST 60 . Both stock and mod versions.
Here is a 73 mph run with a Mod 50 Yamaha
https://www.youtube.com/watch?v=EBgBzwbhPFw

This driver decided to jump the performance to a higher level with a Mod 90/short shaft/ small gearcase/Yamaha.
https://www.youtube.com/watch?v=168f3G-3Tso
Author:  Hounddog [ February 9th, 2024, 12:44 pm ]
Post subject:  Re: What’s Happening With The 70CES Yamaha?
It was an interesting study when I checked into the past history of racers modifying the 42 cubic inch Yamaha triple. Racers in Mod D hydro were messing with them as were the thundercat (SLT) boys. Depending on the class spec rule restrictions they had a long list of successful modifications. There were differences in opinion on porting, cylinder head, and carburetor choices. Those are due to the application the motor is used on. Same mods will not work the same on different types of boats. The purest class with the most restrictions was Formula 50 which was the same boat as SST 45 but with a production model 50 hp outboard. The motors were stock motors, stock replacement parts with a specification sheet for each model motor...the 50 Yamaha raced in that class.

Here are some observations.
The 50 Yamaha performance does significantly improve with modifications for “LIGHT “ boat applications.
You must eliminate the rev limiter.
Weld the crank
Use plastic reeds
Cut the cylinder head a few thousand to increase compression
Blueprint/ match the porting on each cylinder
Shorten the exhaust by 1 inch
Those changes will make a noticeable change in performance.

The next level of modifications gets into porting, carburetor options, intake and reed mods, exhaust types. These mods change with the application and this area has many individual opinions .

Certainly if you have one of these motors. It wouldn’t be a bad idea to do the simple mods when refreshing the motor.
Author:  Roflhat [ February 9th, 2024, 12:56 pm ]
Post subject:  Re: What’s Happening With The 70CES Yamaha?
Would love to try a Yam 90 short on my thundercat. Always keep an eye out for cheap bits to put one together but they don't come up often.
In reality the 70ces I have now is more than enough power 99.9% of the time. Anything other than going for a speed record I don't even use full throttle
Author:  Hounddog [ February 19th, 2024, 3:19 pm ]
Post subject:  Re: What’s Happening With The 70CES Yamaha?
There’s a few posts on the T850 Facebook site
https://www.facebook.com/groups/367495516681441/

The green motor with the large skeg is an OMC 49 .
The 1982 T race video is likely a T750 race with the 60D Yamahas and OMC twins. There’s a Suzuki in the race and maybe some other manufacturers. The Suzuki twin cylinder/ twin carb model did have some success in other classes. I believe Ron Hill’s wife still holds a record in another class running a twin cylinder Suzuki. The motors were crank shaft horsepower rated back then. The Yamaha and OMC were rated at 60 hp. The Suzuki was rated at 65 hp. With a SST 45 OMC spec powerhead engine builders were getting 66 to 68 hp at the crank on a dyno . I have never found any results of a dyno test of a spec Suzuki. But it has a 5 hp advantage to start with.
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