25 to 35hp johnson

[captbone]

I think the Mirage was one of the best engines I did at OMC. The 25 and 35 share the same block and lower unit castings making all port passages and exhaust tuning the same between the two versions. Increasing the bore size of a 25 and readjusting port timing makes it a 35 block. I may have posted some history on the origin of the design in an earlier post. The block is of lost foam construction and due to the small bore size there was a tendency for glue lines to partially block the posts. Unfortunately, this is the case with many of the blocks. Someone willing to take the time to grind out the glue lines, especially in the finger ports is going to be pleasantly surprised at the increased performance. The air box that came with the engine was a patented design and while reducing noise also increased power. I have never found air horns to be of much benefit, although they do look nice. Darn cold here in Chicago!

Thank you for sharing. I would love to hear as much as you are willing to tell about the Mirage 3 cylinder or any other project you were involved with. This is like crack for an outboard junkie. Please share as much as your time can allow as we would love to hear it.

Thanks

Cheers.

[14apache]

I spent hours on the finger ports went from less than 1/8 to a match on the sleeve. This motor has so much torque have had 5 people and still goes on plane.
As far as port timing how much could be gained?

[Ron Hill]

I've really enjoyed these posts! Warm in California. Jim, why not take a week or two and come to California and stay with me???

[NERSTROM]

Ron, tempting offer. When I last checked with Fred he said they were in Oshkosh, I would have been really jealous if he was back in California for the winter. He must be nuts! Still too cold in Chicago.

[Ron Hill]

The APBA Convention is the end of the month (1/14), then Fred said they'd come to Kingsburg for the rest of the winter. You should fly out here in February, we could go see Fred and you could warm up. We are flying down for the Daytona 500 the end of February! I could add that Freddy has always been crazy be it has kept him from going insane!

[speedfreak]

Anyone know how I could acquire a port maps for my OMC 1997 25hp 2 stoke 3 cylinder? As Mr. Norstrom mentioned a few threads above "Increasing the bore size of a 25 and readjusting port timing makes it a 35 block" (on my quest to fully convert my 25hp to the 35hp). I need to readjust my port timing to the 35 hp specs. I've already bored the cylinders to .030 over the 35hp specs. as he mentioned a while back, along with 35hp jets in the carbs. I want to go in and clean up all the glue line in the finger ports at the same time. Any help would be appreciated.

[14apache]

Don't waist your time with the port timing. Open up the finger ports as close to the size of the sleeve as you can. Stuff the crank case if you have time. Want to buy a motor rite now mine has a blown up gear case. Runs like a bear!

[speedfreak]

So no big gains with readjusting the port timing? My machinist said he had reservations about doing that anyway (he was questioning if it would even be noticeable), even if we got the port maps of a 35hp. So it sounds like pretty good gains to be had (noticeable) by cleaning up the glue lines????? I guess stuffing the crankcase gives you a little of that compression back after you clean up the parting/glue lines which actually increases the crankcase volume by doing that? When you cleaned up the glue/parting lines on yours and stuffed the crankcase, was it pretty noticeable from a performance stand point? How about the cylinder head, I still have the 25hp head on mine. The 35hp head was different????????? Anything there?

[speedfreak]

Anyone on this thread have any recent updates on their quest to convert their OMC mirage 3 banger 25 to a 35? I took the easy way out. I bought a remanned 35hp power head, bored .030" over, cleaned all the glue lines out of the finger ports (which were over half closed off) and dropped it on my 15" short shaft. Changed the carb. jets to the 35 HP jets and stuck a set of boyseen racing reeds in it. Should have it back in a few days.

[14apache]

Any updates?