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How do you increase the HP of outboard?

N

Nick0151

Regular Contributor
Hi Guys,

Not planning on doing it just more out of curiosity how do you go about increasing the HP of a 2 stroke outboard. The are lots of video on how to do lots of other 2 stroke engines just not any on those well apart from the smaller ones.

say a 70 HP evinrude 3 cylinder as that was the last one before the v4 I think.

Me just guessing have something to do with the jets in the carbs and timing but just a guess maybe reeds but don’t believe those to have been proven on a dyno.

Again no plans on doing it just want to know.

thanks

nick
 
Smartass answer: Buy a bigger motor. Nah seriously, you aren't going to get much more power out of a 70. Not enough to notice anyway, unless you are racing.
 
A lot of things...porting,boost ports,port timing,compression,exhaust reliefs, reeds,carbs, gear ratio and lower unit type. The SST60 3 cylinder was a stock motor that was modified at factory. It was for the 850lb race class boats and made a lil over 90hp @8500rpm. And they are quick too...
Quarter_Mile_Speed_Record.jpg
 
Fair play to you 88mph and the engine for being able to rev that high 8.5k is high for max hp not had anything that can rev that high since my RX8 and that was 9.5k.

do reeds really make a difference?
 
""do reeds really make a difference?"""

Aftermarket reeds may help in idle and low end but rarely add HP, and that is 1-2HP so realy not felt. Only after7K RPM...other wise stock reeds are fine. After 7K then you look at reed thickness and setup. When we raced we used a steel reed on top and fiber on the botom so they would not 'fan" themselfs at rpm from crankcase pulsations.
 
biggest cheap gain comes from shaving the head ..030'' on up till you reach 180-190 lb compression, and then going up a few sizes on the mains and adding etec reeds and blocks with stuffers. on your motor, they made a 49ci block then 86-93 brideport 56ci then 94' on till close of OMC it was called an oval port. safest mod is to upgrade the block to oval port. much smoother and better midrange.
 
Pistons wont live at that compression as tops too thin ...about 135psi is max. At that compression would need to reduce timing and AV fuel.$$$$
 
I had one that seemed ok, but only ran just past 10 hrs with avgas. I agree not exactly something youd want in a fishing motor!
 
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