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Old 11 November 2018, 07:24   #1
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Country: UK - Scotland
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Yamaha 70hp lightweight cowling

Looking to shave a few kilos off my yam 70hp 2 stroke. Itís already pull start only with no power trim etc. Iíve not weighed the cowling yet but at a guess Iíd say itís 5/6 kilos. Would like to trim a couple off that, just wondering what people do to cut the weight down?
Was looking at a custom made carbon fibre one but looks like it will be very expensive

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Old 11 November 2018, 07:33   #2
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My pal used to race a 3 cyl 90 yam back in the day and he did away with the lower pan (or trimmed lots of it away) and made a custom cowl similar to a clamshell merc split down the middle which shaved quite a bit off the total weight and made access easier to parts usually hidden behind the pan. This was on a boat with remote steering so not sure how that would affect the tiller steering.
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Old 11 November 2018, 07:48   #3
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That would be a neat solution, the lower cowling is metal so heavier too.
Don’t think I’d be allowed to change the design of the cowling with the rules, would have to stay with the same design but could change material and weight I think
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Old 11 November 2018, 15:21   #4
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I wouldn't of thought my cowling was that heavy on my f70, couldn't see it making much difference Personaly dropping just a few kg. I see very little difference in speed and fuel economy whether I head out solo or have an extra two people ( according to my nmea gauges ). I do see a drop in speed and rpm when I have 4 extra adults but only by 400rpm and about 5kmh offtop speed.

Have you tried a run with the cowling off to see if there is any difference before heading down a carbon purchase road. Is this engine race tuned ?
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Old 11 November 2018, 15:35   #5
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Country: UK - Scotland
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Definitely need a cowling for the rules, has to be a standard engine. I've found that losing around 10kg got us from 67.83mph to 70.10mph, which is pretty good going. So a few kilos more removed from the engine would certainly help.

Not tried a run with the cowling off, I'm running the standard airbox anyway, without it I'm sure you'd get more power, forcing air down the carbs!
Engine is blueprinted
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