Optimax to non Optimax lower

[btown101]

I know I have to add the two additional water ports but I have read that the exhaust tuner has to be used from the optimax to the regular EFI Mid section. I got on the parts catalog and my question is they both show the exact same part#s?? The EFI Mid section is a 2001 and the Optimax is a 2004 200xs the two exhaust carry part# 879288t71 for the extension exhaust and the other number is for the tube and its 18276T, I bought a motor with salt issues and it was much easier doing it this way but I want it to be right!! The only thing I see difference is the XS Opti has a plate block off where the EFI doesnt part# 8189091, can anyone chime in to see what I am missing here?? Thanks

[Motv18]

As far as I remember the foot was a foot. The opti had other parts iirc. Different displacement and stuff.

Their were issues if swaping fatshafts, or putting a large on a mid. And naturally changes in lengths.

Never did the swap myself though; the mod guy did that. But 4s to opti or vise verse was more or less a bolt up. Not helpful but that’s where the 2 cents is from.

[btown101]

Thanks, I am assuming they are the same other then the two fittings on exhaust plate which one is air dump and the other is water strainer. I had read here that the Tuners were different but after i looked both serial#s up and compared parts they are identical which saves me from having to tear into the mid section. It took me 3 hours and some nice curse words to separate the power head it was so welded from the salt, needless to say I have a mid section for a boat anchor now!! LOL

[Fishinmymission]

FYI don't make the same mistake I did with that assumption if you are messing around with plates from different motors and years. I ended up with no fittings to drain thermostat water back into the exhaust and I dead ended my bleed air so it actually went into a sealed pocket between the upper and lower plate. Some mods allowed me to fix everything without taking off the powerhead again luckily. Ensure you either have another fitting in the aft of the upper plate that you can T your two thermostats together and let that water go into the exhaust (this was the early design and what i have been running for the past year, I did see some blistering on the water alignment tube tool but not sure if this was chemical or overheat damage, lower unit seals and water pump housing all appear great). The new merc design ts the two thermostat lines together and puts them into one fitting in the aft of the lower plate for the 200xs and does not t them and uses both fittings in the lower plate on the 175hp.
Some usefull information below.
https://www.screamandfly.com/showthr...5-carbed/page2

[btown101]

Yes I am aware I have to drill and tap the lower plate for the air and water return, I am going to hang the EFI mid and then copy the XS Mid locations of the fittings and location. I will first attempt to just swap the plate but I honestly dont believe I can get it off salt water mid. I have never dealt with salt water stuff and had no idea what that chemical reaction could do to the various metals.

[Fishinmymission]

Mine was a 1995 carbed saltwater(like marina 6 months a year) that I had to take apart.
I damaged my upper plate by having a crane lift the power head while my boat was in the water. The boat lifted out of the water by the powerhead, what finaly freed it was me swaying port to starboard in the boat until the boat dropped. The studs came out at an angle and cracked the upper plate.
Once you get it apart work from there