3.0L mods & specs

[bigdan1]

first post here ....
just bought a 1987 doral 160 open deck with a mercruiser 140HP 3.0L with alpha one .....

I wonder if it would be worth modifying the engine
comp cam 260H , port the head , bigger valves, better springs etc...
anyone ever did this ?

I need some specs on the engine .I downloaded the engine manual
but all they give is the bore at 4.00 inches ...
what is the stroke on these ? valve diameter int & exh ?

thanks for the inputs !

Dan

 

[Howard Sterndrive]

Re: 3.0L mods & specs

there's no Comp cam for a 3.0

total waste of time.

All your "mods" are designed to help an engine breathe better and therefore make torque at higher rpm.

But, your 3.0 is already turning 4600 rpm if you have the right prop, and that's all the valve train is designed for. It's a 1960's pushrod engine that has not evolved. There are no trick parts out there. no manifolds, carbs, no exhaust horn big enough...and thru hull on a 3.0 would sound gawd-awful

It is also all the u joints, gimbal bearing and outdrive is designed for.

If you budget $5K to $8K for the motor, plus another $1K for regearing the outdrive to 1.81 or 1.65 ratio, you might be able to work that motor up to V6 levels... just before it blows up
you could probably buy a reliable V6 boat for less

your boat probably has a 15 gal fuel tank, 5/16" fuel line and manual steering...none of which are convenient once you exceed 170HP

 

[Don S]

Re: 3.0L mods & specs

Most competition cams aren't run in boats with water in the exhaust. What happens is a thing called reversion. This happens from valve overlap and sucks water back into the engine. The 4.3 V6 is also very suceptable to reversion, moreso than a V8
OMC (when they existed) Mercruiser, and Volvo have been squeezing every last HP out of those engines for years. Doubt you will find a magic bunch of HP not already found by others.

 

[bigdan1]

Re: 3.0L mods & specs

Don ,
it`s just that i tought that he same modification procedures that aplly to a car would,for a marine engine ......

I know I have to keep a fair idle ( otherwise too high and I would ruin my outdrive )

I just wanted to give 20 hp gain with a ported head , a little bigger cam
(212 dur nstead of 206 like original+ .050 lift more ))+ better springs

total cost would be around $500.00

ID like a V6 or V8 too ,but someone told me that a 3.0L is good on gas consumption ......