bolt on horse power for 120 v4

[N Wolf]

I'm looking for bolt on power for my 1990 evenrude 120hp. High performance heads and the like. Im just looking to gain about 15 hp total, not all out drag boat power. Any ideas where to look?

 

[Bob_VT]

Re: bolt on horse power for 120 v4

I'm looking for bolt on power for my 1990 evenrude 120hp. High performance heads and the like. Im just looking to gain about 15 hp total, not all out drag boat power. Any ideas where to look?

Will not happen. That 120 is already upgraded to the maximum because it is actually 135-140 HP at the powerhead and the 120 is measured at the prop. That 1990 120 is more powerful then an older (pre-1983) 135.

You want more HP then go with a bigger motor such as a 150.

Any modifications such as shaving heads, changing the ports, or carbs will reduce the reliability as a good motor and will then require constant tinkering.

 

[Frank Acampora]

Re: bolt on horse power for 120 v4

Horsepower is basically set by port timing on these two cycle engines. Unless you want to tear down the engine and modify porting, more horsepower just "aint gunna happen".

About the only bolt-on you can try is aftermarket reeds--and I don't know whether or not they will add horsepower to your engine.

If you are not using a stainless prop. invest the 400 bucks for one. Usually, the same brand and size stainless will turn 200 RPM faster than aluminum with an increase of about 2 MPH top speed--that's like adding 15 HP.

Similarly, a Jackplate may allow you to run the engine higher on the transom for less drag and higher speed. A nose-cone has no advantage unless you are going over 60 MPH or so.

 

[nwcove]

Re: bolt on horse power for 120 v4

i agree with the above posts, modding the motor will most likely result in it being unreliable for everyday use. id go with a performance prop, remove any unnecessary weight from the boat, and clean and wax the hull, you.d be surprised at the difference you "may" see in top end speed for a few hundred bucks and some elbow grease.

 

[metriccrescentwrench]

Re: bolt on horse power for 120 v4

About the only bolt-on you can try is aftermarket reeds--and I don't know whether or not they will add horsepower to your engine.

Someone at ScreamAndFly did a test of aftermarket reeds. Just replacing stock reeds had negligible effect on horsepower or top end speed, though aftermarket reeds did provide a smoother idle. The only reed related mod that helped top end power was cut reed cages, which helped airflow into the engine.