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Yamaha 70 @78mph on a Thundercat
http://ww.w.hpbc.ca/viewtopic.php?f=19&t=4393		 Page 1 of 1
Author:  mattmak [ May 1st, 2022, 2:24 pm ]
Post subject:  Yamaha 70 @78mph on a Thundercat
Some amazing effort in this endeavour:

78.1mph reported, CNC cyl head in the works, etc..

https://www.rib.net/forum/f50/my-thunde ... 12-22.html
Author:  sharpeye Mike [ May 1st, 2022, 8:52 pm ]
Post subject:  Re: Yamaha 70 @78mph on a Thundercat
Thanks for posting Matt.
It's been way too quiet these past 2 years
Author:  Roflhat [ May 3rd, 2022, 11:51 am ]
Post subject:  Re: Yamaha 70 @78mph on a Thundercat
mattmak wrote:
Some amazing effort in this endeavour:

78.1mph retorted, CNC cyl head in the works, etc..

https://www.rib.net/forum/f50/my-thunde ... 12-22.html


Thanks!
Not sure if I'll keep pushing for records or not. Still got plenty ideas on how to go faster it's just a lot of effort and time
Author:  mattmak [ May 3rd, 2022, 8:04 pm ]
Post subject:  Re: Yamaha 70 @78mph on a Thundercat
I can imagine there are diminishing returns at various points..
And that "extra" effort here an there that isn't typical (like the cowl)..

It is very cool that you are documenting that project.

Only reports of Yamaha 70 speeds I've seen on our side of the pond are a factory stock 70CES at 67/68mph on a t-boat, and a modified Yamaha 70 doing low-mid 70s mph, similarly on a padded v-bottom.. Completely stock and original long shaft, small case 1987 70hp on my heavy Voodoo did 62mph. So 78 seems insane.

I have a 70 in the works - do you have any tips for measuring phasing of the crank, and pinning/welding it? Just check for runout and tig it?
Author:  Roflhat [ May 10th, 2022, 2:04 am ]
Post subject:  Re: Yamaha 70 @78mph on a Thundercat
A more efficient hull would be the next step, the current one has too much angle on the floor. Too much bow lift which makes it unstable and generates too much drag.
Hopefully get another carbon cowl made, and I've got a big pile of carbon to make a new stiffer floor although I might get a new hull first.

Definitely possible to get a lot out of these motors but it's not easy. I had a lot of help from my late friend Rolf Magne Sunde, he did the porting on the current block and a lot of advice on other things. His knowledge on these motors was truly phenomenal. I'm sure 80mph is possible, but as you say just how much extra effort is required I don't know...

My own crank I sent to Chris Applebee here in the uk. He specialised in racing cranks for outboards/jetskis and holds a couple records of his own
Author:  Hounddog [ January 21st, 2024, 12:02 pm ]
Post subject:  Re: Yamaha 70 @78mph on a Thundercat
Good idea to re-read these posts. This was the start of the project.
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