Flat Back Repower

[Boston_FB]

I have a '70 22-2 that is about to outlast it's '92 200 hp outboard.  So I am heading down the repower route.  I welcome any comments to the following questions:

I am currently getting about 30mph at 4200 rpm WOT.  So, I think this engine which has a decreasing compression is operating at a low level of performance.  Considering that today's engines are rated at the prop, should I be considering a 150, 175 or 200 hp model?  I don't want worse performance than I am currently receiving.

I am looking hard at the 2 -stroke E-Tec because of their lower weight and the fogging feature (I am a northerner).  The weight is important because, like many other old boats, mine is sitting rather low in the water so additional engine weight is not what I need.  Current engine is 455 lbs, Etec = 418 lbs, Yamaha 4-stroke = 487 lbs.  Any good reasons I should be avoiding the 2-stroke?  Other alternatives?

Thanks for any guidance you can provide.

[GoneFission]

I think you would be happy with the eTec (433 lbs for the 25" model in 150, 175, or 200 hp) or the new Mercury 150 FourStroke (at 455 lbs).  The newer 150/175 models, when with the right prop, would give very good performance with your 22-2 flatback.  You don't need a lot of power on that boat - 150 seems to make most folks very happy.   :pl:

[Boston_FB]

Thanks much for helping me with this.

[fitz73222]

Thanks much for helping me with this.

Sounds like you have a very sick and / or a very overpropped engine so comparing performance numbers to that engine would not be wise. Optimum flatback power is always a sprited discussion on this forum. I always listen to the people that actually own one and it seems that 150-175 is the sweetspot horsepower for your rig. Once your boat starts going over 40+ mph, she is out of hull speed, so more power tends to deliver diminshing returns. One of our members Capt'n Matt, makes a full blown living out of a restored flatback down here in Florida and started with an Opti 175 and recently went with new I4 150 Merc 4S and appears to love it on his guide boat. He would be the one to listen to on flatback power. Try sending him a PM or someone here on the forum can reach out to him. I'm actually curious myself how that engine is holding up for him.

[fitz73222]

I guess one thing to consider here is are you still running with original open transom? Engine weight does become a greater concern assuming weight gain from wet foam which is a given on our old boats.

[Aswaff400]

i  have been on Capt Matt's flatback, and she flat out rocked with the 175 optimax. she was a rocket out of the hole and cruised 30 mph burning about 6 GPH. i havent been on his boat with the new 150 4 stroke yet, he did say performance was pretty close to the optimax.

i will be powering my flatback with a Merc 225 EFI, its way more HP than any flatback needs but i couldnt pass on the price!

[Capt Matt]

A 150 is plenty of power, I love my 4 stroke mercury it seems about the perfect power plant for a flat back
Another plus: it's cheap to service
700 plus hours already, no regrets
Capt Matt