The reason I water-cooled the head is because so much of the cowling had to be removed air cooling would be not be sufficient, I have left the fins on the flywheel to help cool the crankcase, some of these engine mods the fins are machined of to save drag. I have managed to get a new very cheap carb not a walbro but almost identical with a 13.49 venture.
Because of the type of hull I have had to use a wtc tune pipe therefore I have no choice with the header, yes a compromise but it remains to be seen what performance I will get.
A stock zen 260 PUM produces max power of 2.16kw at 12000rpm and max torque of 1.94 at 9500 rpm, with cylinder displacement of 25.4. The 14000 rpm is obviously not under load
The weedworker has a displacement of 28.2, according to my calculations I will get a torque figure of over 2.00 at 9500rpm
I have been modifying petrol engines for nearly 30 years the first was a 22cc McCullock chainsaw engine which held the spark ignition (as it was known then) record in 1984 of 32.4 mph in a boat I designed and built which I still have
and won many offshore races which incidentally weighs nearly 14 kgs. The problem was they were fitted with points and condenser and not very reliable when they got wet, also the flywheels tended to burst at high RPM. With horrendous results.
My friend Naviga world champion 1988, 1994 & 1998 Dave Marles who has been designing and racing boats for many years suggested the prop size all due respect but I would think he has more experience than yourself and I value his expertises.
As for is it worth the trouble, I do not have a bottomless pit, if I can get the engines performance to equal the stock zen for less than 30 quid, I consider it to be well worth the trouble.
Everyone is entitled to their opinion and suggestions are always welcomed
Incidentally the Mercury Cat I built has been officially timed by his club at
64.3 mph with a stock zen a 257 carb.
Glenn,
the exhaust duration is 164 degrees
When we look today, we see incredible speed records and high standards of competition. We've learned that speed means serious attention to details and that our models require the best materials and demand our very best driving skills. Engines and radios provide nearly flawless performances, and the difference between winning and not boils down to each individual's performance, preparedness and motivation There are two things that I am absolutely certain will remain the same; speed records will continue to be set and broken, and the skills and motivation of the modeller will be the deciding factor as we continue to raise the bar to new heights. I hope we can continue to have fun along the way.