Your results will be VERY interesting Ron! Post up your comparison #s as soon as you get some accurate data back from running with the Xs.......

I hope you are right Tom! Will do final testing on the smartcraft this week. If all goes well finally ready for swap over. Just installed new Mike Nass skirts to replace the plastic junk Mercury had.
Hope to have it running by Christmas. Work is crazy from the Boat Show and just bought a warehouse condo so we have to relocate by Jan.
Going to be quite the man cave.

Did you do a compression and a leak down test before the rebuilds. Also did you mount and run the engines before the tare down. Would be cool to see how much real speed you got after the quality rebuild you did. After rereading this post and a Lagavulin or two, I take it your comparing a 300x with 300xs, correct? How much was the rebuild, parts only. I only ask as I purchased a 300x, with 10 hrs but wasn't properly stored away. Sounds totally different when fired up beside my other engine with 140 hrs. One a 2003(low hrs), other 2004. Compression almost the same, 148 +- 2 in all 6, and 142+-2 in 140 hr engine. Injectors cleaned and flowed on both engines same date. Is there anything flaw wise on these engines I should look for?

Andy, Unfortunately because I could not plug n play the x motors with the newer harness etc and not knowing the status of motors I did not run the first. I did do a compression test and all cylinders were 148-150psi. It was my plan all along to go through the motors top to bottom. The motors according to the computers had less than 300hrs on them and not a lot of high rpm usage. Some of things we found were a piston or two that did not look heathly, burnt multiple reeds on the reed cages, Injectors test good but were cleaned. Also found some wear on one of the cranks so replaced that as well. Took apart and replaced all bushings, seals etc in the mid sections.
Rebuilt both fuel pumps and replaced all hoses on motors for oil and bleed lines. All new pistons, bearings, and a few rods. I would have to say I have spent about 10k in parts, painting, decals etc. Not including any labor.
With that said I believe these motors to be better than a factory new one from mercury!
I would pull the heads off the motor and look at cylinders on the one that was not stored and see if you can see anything on the walls.

Thanx for the input/advice. Will do next month. Andy...

Good luck Andy, I am not an expert by any means but would be happy to help with any questions or concerns you may have. I had one of the best outboard mechanics on the planet help with the internals of the motor that has been at TNT and building/repairing and racing outboards for over 40 years.

Motor swap begins
 

Started derigging the Optis today. Removed rig tube and remote oil fill. Installed new rig tubes. Note my custom plexi adapters to cover the larger holes. What do you all think? Will install new motors tomorrow.

Good to see such attention to detail.

Adapters look great, wish I was there to help swap power��

Ron, Looking great! Keep us informed on the "project".