converting a 1990 evinrude 20hp

[Jeremy1986]

I was wondering if was to buy a 35hp carb in the same year will it increase the horsepower and if so what do i need to do this conversion. what year range carb will fit my motor. any help would be helpful. thanks to everyone and happy new year. thanks again.

 

[tx1961whaler]

Re: converting a 1990 evinrude 20hp

Intake manifold and carb are different between the 20, 25 and 30-35. May be some other stuff is different (port timing, etc.)
Compare the different models and PN's here: http://shop2.evinrude.com

 

[G DANE]

Re: converting a 1990 evinrude 20hp

Any carb from a 1978 and up 35 HP would fit. Since yours have the primer setup, a carb from 1984 and on probably would be better, and preferable, since they increased the carb bore size from 1984-85 when they started going with prop rated horsepower. Any 35 hp carb will give you more HP, though. On some vintages you will have to increase the hole in intake to the size of carb. You will not get to 35 HP on all years, many years 20 HP have low compression head.

 

[Bumpa53]

Re: converting a 1990 evinrude 20hp

Hi all....

I read this thread with interest (who doesn't want more HP ?) and wonder if the power increase will be realized. Since power is based on fuel/air ratio, displacement and compression ratio, wouldn't the 20 and 35 HP need the same piston diameter and stroke to make 35 HP ? I couldn't easily get the specs to check.

For the same top end there is a benefit to a larger carb via reduced pressure drop (carb throat and intake manifold diameter) because higher pressure at beginning of intake stroke = higher pressure at ignition.

If the 20 HP top end is indeed identical to the 35 HP then bless the engineers at OMC and an extra Happy New Year to Jeremy1986.

Bumpa53

 

[bgbass.1]

Re: converting a 1990 evinrude 20hp

you need to change the intake as well as the carb. done it on a 20 to a 30

 

[Jeremy1986]

Re: converting a 1990 evinrude 20hp

thanks for all the help guys