hoting up 68 18 hp evinrude

[OMCFREAK]

g'day i am toying with the idea of hoting up my 18hp. is it possible to file of drill the ports on each cylinder to a bigger size? nad if it works how much difference will it make? and if i run if on shell A fuel(Race car fuel) will it damage the engine? my mate used to do this with his motor bikes back in the 1950's.

 

[Paul Moir]

Re: hoting up 68 18 hp evinrude

You might try something a little more conventional or proven. That 22.0CID block was sold in 20 and 25hp models too. I don't know what the differences are, but I'll bet someone here does.<br /><br />Search this forum for a "pegged curiosity meter".<br /><br />EDIT: Some links:<br /> Link 1<br /> Link 2

 

[Dhadley]

Re: hoting up 68 18 hp evinrude

A very interesting thing about those motors -- the blocks were almost the same. The 25 crank was "balanced" and the wrist pin is actually lower in the 18 and 20 piston so the piston comes up higher. You'd think the 25 would be the one with the lower hole. Anyway, the heads are different too. <br /><br />When we raced in that class, 25SS, thats what we used. A 25 block, crank and head with an 18 piston. It worked great on a raceboat but we tried it a couple of times on a small aluminum Starcraft but burned a piston both times. We also used a carb off of a 50 or 70. <br /><br />But youre back to the same old scenario -- if you arent twisting the 18 now pretty high, you may not see any difference. Especially if your boat doesnt respond to small torque increases.<br /><br />If you were inclined to try something, I'd just get a 25 head and try that. Your compression will be higher so you will have to run the good fuel. Just try it and keep a close eye on the pistons. I'd jet it up to the point it "blubbers" and then back down.<br /><br />Good luck!

 

[Chinewalker]

Re: hoting up 68 18 hp evinrude

Dhadley's right on the money. The 18s really don't avail themselved to much "hopping up" beyond the 25hp updates. Running racing fuels won't do anything but empty your wallet quicker.<br /><br />Also, modifying the motor without addressing the clubfoot lower unit and the general lack of performance propellers for it will mean anything major you do to the powerhead likely won't be translated to the water.<br /><br />What are you running it on for a hull? What's the current load? If you simply want to go faster with your fishing boat, get a bigger motor. If you're running it on a small Sea Flea speedster, then you might want to look for an old 2-blade Michigan wheel from the AJ-series. Set-up is just as important, if not moreso, than hop-up...<br /><br /><br />- Scott