3 projects going on,,,,200 Crossflow Johnson 1st one help needed

[omcforever]

Need help. I am looking for the factory late 1970's 200 Johnson crossflow port specs(intake and exhaust). Diameter/length/width/distance from top of cylinder to top of ports....ect. Pictures also if possible. Have a 1981 150 block that I am going to port to 200 specs.(have a machine shop that can do it)...Any help would be appreciated...Art

[keefallan]

I Believe that the 200 and 235 shared similar ports.....with the difference being the bubbleback and larger carburetors. Dont hold me to that, because I have never been able to compare them side to side. I have compared visually the intake transfers of a 150 to a 235 on numerous occasions. They are very similar...transfer side only. When I say this, I am saying that I looked at the ceiling height of the transfer against the wall of the inspection area. The little amount of space that is there was almost identical. This is just to give you an idea of what I found. I never actually took measurements back then. I have learned a little more since then. Where the biggest difference is gonna be is on the exhaust. The exhaust ports of a 150 have very tiny ports. Whereas the 200 has ports similar to the 235.

Hopefully someone chimes in with actual heights.

[omcforever]

I Believe that the 200 and 235 shared similar ports.....with the difference being the bubbleback and larger carburetors. Dont hold me to that, because I have never been able to compare them side to side. I have compared visually the intake transfers of a 150 to a 235 on numerous occasions. They are very similar...transfer side only. When I say this, I am saying that I looked at the ceiling height of the transfer against the wall of the inspection area. The little amount of space that is there was almost identical. This is just to give you an idea of what I found. I never actually took measurements back then. I have learned a little more since then. Where the biggest difference is gonna be is on the exhaust. The exhaust ports of a 150 have very tiny ports. Whereas the 200 has ports similar to the 235.

Hopefully someone chimes in with actual heights.

Appreciate the input.....Have a couple 150 flat back blocks and a 175 bubble back
block and a bad 235 block. Guess I could map something in between...LOL..

[omcforever]

My brother has a machine/cnc shop so all he needs are specs/ect,,,and then let her rip. It has been nice over the years to have free machining. Just never dove into porting because of all I do not know about it.. Trying to build a flatback 200(have all the right carbs, heads, ect). Going on a 19 foot hand laid Stratos bassboat rated for 200HP being restored. One of my many winter projects(restoring old bassboats and old OMC crossflows).

[keefallan]

Take measurements with that 175 block.........and see if they arent the same as the 235 and then compare them to the 150. See if the intake transfers are all similar in regards to height and size. That 175 was the defunct 235 after 1985..........at least thats what my guess is. In fact, I think the sleeper motor of the crossflows was the big bore crossflow 175. It had all the goodies of the xp175 and you didnt have to pay for it. There is only one set of carbs for the 175 and xp175 of the same years.......same jets etc.

I think what others would say is to use a degree wheel and rotate the crank/piston to find the opening and closing events of the 235, and then grind the ports of the 150 block accordingly. That will be the most accurate way of replicating ports from the one engine to other.

If you just squared up the ports on the 150(especially on the exhaust) you would be surprised at how big that port becomes. It will become almost as big as the transfer port. Its been a few years since i did a 150's exhaust, but they become quite big(exhaust ports) from what they were. You realize, that you can put either one of those other motors and have more horsepower. That 175 makes much more than 175 as it sits. The 150 ported to a 200 still wont bring you 200 hp. That 200 rating was before prop rated hp. It will bring you to the 185 mark. The late 80's 185 was the 200 rebadged after hp ratings changed.

[perfmarine1]

It really depends a lot on what Boat you have how far you can go with the porting on a cross flow you don't want to lose bottom end if your boat is heavy

[keefallan]

perfmarine is right..........the 150 has much more low end grunt than the 200. That 175 of yours has plenty of low end grunt tho........