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| Tell Us About Your Mod 90 Yamaha.....lessons learned? http://hpbc.ca/viewtopic.php?f=19&t=4677 |
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| Author: | Hounddog [ December 6th, 2024, 1:39 pm ] |
| Post subject: | Tell Us About Your Mod 90 Yamaha.....lessons learned? |
I was surprised that Thom had been running a Mod 90 Yamaha on his critchfield for a few years. I know that there were at least 2 Mod 90 Yamahas being built to race in 0PBRA 3 cylinder drag. Jason Johnson who drag raced Mod90 Yamahas for several years has communicated with several of the Mod 90 Yamaha builders. Hydro Tec has supported several drag racers in the 3 cylinder drag class in the southern states. My interest in the 90 hp Yamaha came from my communications in 1996 -7 with the Tech Representative at Yamaha Japan concerning my 70CES Yamaha. They were helpful in providing the document testing information about my 70CES. I just happened to ask if they had looked at the 90 hp to see if there were similar improvements to it . He said not as a Yamaha project, but they had done some initial testing. He fax’d me a a handwritten sheet with a diagram and notes. I few years later 1998-9 I built a powerhead to those specifications. The result was very similar to the characteristics of the Stock 70 hp Yamaha to the 70CES. It was high idle and better performance on a light boat. Porting changes were minor. Compression was 165 psi. Just like the 70CES the maximum hp is at 6400-6500 rpm. Jason Johnson began his builds later. His first builds had large increases in porting and over 200 psi. From reading many of his web posts he now suggests less porting and less compression. He still has custom parts on his motors, but suggests there is little if any advantage over modifying stock parts. He is also suggesting compression 180 psi or less. I have heard of Ontario builders doing huge exhaust ports, but I have not heard how those motors performed. The highest hp at the crank I have heard of was 132. It seems very easy to make 110 hp and those motors run very well and last. Once you push for more the motor is more difficult. |
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| Author: | Hounddog [ December 7th, 2024, 6:42 pm ] |
| Post subject: | Re: Tell Us About Your Mod 90 Yamaha.....lessons learned? |
Old thread from 2017 about mod motors. Interesting about the nose cones, the 42 cubic inch motors and the 2.4 gear ratio in a drag setup. I did assemble an SST 60 gearcase with the 2.4 gears just to try it. I ran a 25 pitch 12 3/4 diameter prop. The hole shot was much better and in 660 feet it was turning over 8000 rpm. I wished I had a 26 pitch to try. https://www.boatracingfacts.com/forums/ ... ture-parts |
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