which 5.7 350 tranny combo fits F26/261?

[Marko]

Hi,

Has anyone fit a 350 into a F26 or 261?

Time to finally repower my '82 261. Currently a very tired 318 w/inline Velvet Drive 1:1. Will replace both engine/tranny & keep boat for decades.

Who has done this swap?
- Did you change from inline to down angle tranny to save space?
- Which engine/tranny combo where you able to fit, with what mods to structure or hatch?
* engine space dimensions may vary year to year, but interested to see what has fit in other F26/261
* I will likely make custom engine hatches for better access than 1 original provides, so can increase hatch clearence slightly if needed
- My target engine is Mercuryremanufacturing 5.7 357 Horizon which gives enough power yet can keep 1" shaft
* not after speed, need better torque get on plane loaded
* mercruiser for broad service access, plan to cruise Great Loop (E US) and Canadian Canals

[Paul]

I installed a 350 GM (carburated) in my '78 F-26. It was a fairly easy swap for me since the previous engine was a 305 GM. After aligning the strut, shaft, coupler and engine mounts, I had an interference problem between the flame arrestor and the hatch cover. (the 350 required a taller flame arrestor) I resolved this by milling a pocket into the bottom side of the hatch with a router, then sealing it back up with a layer of roving and resin.

The trans is a 1:1 Velvet Drive turning a Ø1.0" shaft with a 14 x 9 NiBrAl cupped propeller.

[Marko]

Paul, is yours an inline tranny? not a V drive? What engine make & hp did you put in?

My set up same except still have 318, repower planned winter 15/16.

Height likely main issue. Did you consider, use, or know anyone that used, a down angle tranny? ZF makes a 8 degree down angle. The 261/F26 shaft is 15 degrees. The 8 degree down angle, if fits, should shave 2.5" in height with engine at 7 degrees toi hit 15 degree shaft angle.

My hull to bottom engine height 33" at front, the Merc 357 is 31.5" if mount flat, but assume need to tilt 7 degrees + 8 degree down angle bringing front height to 34" in a 33" space, so mod hatch. The Crusader 5.7 looks to be 29" high, maybe less hatch mod.

The Merc 357 is 310 hp & relatively flat torque of 370 @ 3200rpm compared to 318 225 hp & ~295 torque @ 3200rpm.

[Paul]

My trans is in line, not V-drive. The 305 engine that was in there before was a 228hp MerCruiser. The 350 that I replaced it with is custom built and produces about 300hp. It is based on a 260hp MerCruiser design with a few tweaks. I'll dig up a few pics of the set up and post themfor you.

Is the new engine that you're looking at injected or carb?

[Marko]

Thx on pics. Going with injected for reliability/economy.

https://www.mercurymarine.com/en/us/eng ... -inboards/

Merc factory rebuilds their 350cid 5.7 Horizon, slight bore results in 357cid 5.8 Horizon w/3 year factory warranty. Choosing merc for easy service access when we later cruise eastern US & Canada, and will have Merc service shop do install. Enough increase in hp/torque over 318 to plane/cruise well loaded. If more bite out of hole wanted may try 4 blade prop, don't care about speed.

Engine hatch may custom fab new out of aluminum if clearance needed (existing hatch is a heavy fiberglass I had made when original got soft). Likely will cut in large 2'x3' hatches either side of engine for better tankage access without disturbing structural. Tired of pulling exhaust risers off to access these areas.

Was changing prop, or banging prop pitch, needed when you upped power?

[Paul]

I was able to up the pitch to a 14 x 10 with the engine upgrade however I've since added allot of weight to the boat (generator, AC, tender, etc) so I had to switch back to the 14 x 9 which gives me the rated WOT rpm.

[Paul]

Below are a couple of pics as promised. In the first one, you can see how the flame arestor appears almost even with the top edges of the hatch opening. It is actually just below.



In the second one, you can see how close the front is to the bulkhead. You can also see the access door that I put in behind the cabin steps. This allows easy access to the front of the engine for service. To clear the space under the steps, the batteries were relocated to behind the shaft log. This can also be seen in the picture.



Any questions, let me know.