hopping up 1977 v6 200 hp evinrude porting - milling heads- need information

[rockbottom]

someone out there has the information i need , how to port and mill the heads on my lastest boat 20 ft tahiti 1977 with a v6 200 in pretty good condition , help anyone , steve

[terry taylor]

someone out there has the information i need , how to port and mill the heads on my lastest boat 20 ft tahiti 1977 with a v6 200 in pretty good condition , help anyone , steve

HI.if only answers came easy. Porting is a specialty and must be done from experience and knowllege. Have a machine shop remove 40 thou. from the heads and run premium fuel thanks.

[rockbottom]

thanks terry , that a very good point there is no easy answer , I have experience to do the job i was wondering if someone knows to square off the ports or to raise them widen lower and which side intake or exhaust and how much i need someone who has done the job before , you said .040 that would raise the compression how much ? I always run super with lucas fuel additive to control pinging from what i can see most 2 stroke outboards that get HP builds are bridgeport mercs but Im gonna try my evenrude , steve

[terry taylor]

Take your compression readings and post. Maybe responses can guide you with added information thanks.

[rockbottom]

cold compression- throttle plates WFO -115 psi on all 6 , thank you,steve

[racer]

If they are original heads cutting .040 may be too much and they will hit at rpm, you need to maintain .040 clearance when cold. I would not raise intake or exhaust porting but you can clean match them and remove casting flanges. It will need to be rejetted and reduce timing 2 degrees.

[rockbottom]

Thank you Racer , before actual cutting anything i'll cc the head and compute the ratio , while doing this port matching what finish is best inside the actual ports ? please keep in mind that i have experience in porting automotive heads, so polish or use the carbide ? and what if you know is the max rpm for continous use ? do people lighten the flywheel ? balance the rotating assembly? are there better pistons or are the stock forged ? are there shops who hop up evinrudes ? thanks for your time ,steve o yea my wife and me love to ride over to cooks corner on our 1977 BMW twin- nice area

If they are original heads cutting .040 may be too much and they will hit at rpm, you need to maintain .040 clearance when cold. I would not raise intake or exhaust porting but you can clean match them and remove casting flanges. It will need to be rejetted and reduce timing 2 degrees.

[terry taylor]

HI. i,m not questioning you,but I am the theory. Raising comp. is said to be one of the better ,easier ways to increase power and a bonus is it happens useing less fuel. To my thinking jetting richer and retarding timing is canceling out some of the benefits of raising comp. Open question to all, where does the extra fuel mix go when the space for even the stock fuel charge is smaller thanks.

[rockbottom]

thank you terry and racer and any one else interested in high performance outboards, I suggest we start a new thread on this topic so , I will- look for a new thread subject raising compression

[pcrussell50]

rockbottom,

racer is being friendly and modest, and classy, by not soliciting you. BUT he is a very experienced OMC builder/tuner, who is highly regarded around here. And the best news is that he is relatively local to you and me. With expertise like his right at your doorstep, I wouldn't even consider doing my own mods that involve machining and grinding myself.

-peter

[racer]

Terry,
Yes jetting up will cancel some of the added compression benifit but needed to keep the engine alive especially on todays fuel, remember that engine was built when fuel was much better thus already had more compression than a lot of todays engines. The added fuel percentage needed is small, compression changes the explosion in the cylinder (pressure) and heat, without the added fuel it will most likely melt the intake corner of the piston, it is always better to be safe and work down than be on the edge right off the bat.

[rockbottom]

peter ,

thank you , i'll give him a call , steve