Yamaha 75 to 90hp conversion

[Willem Wikkel Spies]

Hi Jim

thank you for your reply.

yip i have done quite a bit of research on the engines.

according to the parts list, the heads and cylinder sections are different between the 75 hp and the 85hp.

thus i suspect that the higher compression is due to a smaller head on the 85 or that the pistons deck height on the cylinders are different.


what is the chances that the exhaust port open sizes is different.
i do not have a old engine at hand in order to check the port sizes etc.

this is info which i am looking for.

we do the following type of launching when going to fish.

https://www.youtube.com/watch?v=UsAxJRcLeH8

so ja, the extra 30hp will be welcome for these launchings.

2x guys up is one thing, being 5x up is a extra 300kg which will delay you a bit.