Mercruiser MR outdrive question
 

I have a '78 IMP 26' with twin 260's and Mercruiser MR drives.

I'm told these are the precursor to the Alpha drive. Does anyone know what hp these drives can handle?

Thanks.

fixx
 

up to 425 hp if your easy,,have a friend with a 383 500 hp and a alpha ss,,no issues..i saw a 1980 scarab panther with 425 hp big block with alphas,,you just cant beat on them with alot of power,,

I had some on my nova, granted the motors were only 188s but I drove the hell out of it , launched it etc... and they held up fine. they werent fresh either. Dtive it like you stole it, when and if they let go replace 'em with the sei's.

They do ok on on a light boat with up to about 350 horsepower. In a heavy boat with big torque they strip the upper gears on a hole shot or catching air. I have seen standard Alphas disintegrate in the ocean within hours of putting them up against a big block. You can get away with it for a few months on a lake if you take it easy. If you push it keep spares...you will need them.

I blew up an alpha behind a 454. On the first hole shot with all 8 plug wires! It held up for a couple minutes with the 454 on 7 cylinders though :D:lolhit:

330hp/8 cylinders is 41.25 hp per cylinder x 7 cylinders = 288.75 hp... So with a merc 350 (260 hp) you well within keith's saftey margin....

And while we are doing math... 7.4 liters = 7400 cc's
7400cc/ 8 cyl = 925 cc's per cylinder

925 cc's makes 41.25 hp
My quad, naturaly aspirated on pump gas makes 50 hp with 200 cc's

41.25/ 925 = 0.04 hp per cc
50/200 = 0.25 hp per cc

Given the yamahopper is a 2 stroke we will be kind and cut that in half so
0.04 hp per cc merc
0.12 hp per cc phragle

Mercury needs to get their act together because a Phraglized air cooled yamahopper is kickn their butt..

The mr is not the same as the alpha. It came out before the alpha and is interchangeable with the alpha.

I have an mr behind a warmed up 188 (302 ford) mine makes around 300 hp and is in a 1975, 19 foot, searay.

Mine has held up fine with yearly gear lube changes. No hole shots or air and it will survive behind a 300 hp smallblock.

the 78 has the spring pin in the top of the drive shaft.makes the top of shaft the weak point.i have seen many broken there, snapped one myself with a 400 small block and a 79 sundancer. (never try to make a sundancer go faster.) anyway, as sprink said, start shopping for spares now. best buy is a 500 buck neglected, never used, pos rotted out mid to late eighties cuddy with a 305 in it. strip the parts, scrap the hull and sell the trailer for more than you bought the whole package for. a v6 or 4cyl drive is wrong gear ratio.

Almost a good argument. The math is right but You forgot about cylinder size. The Smaller of the cylinder size the higher RPMs it can spin. My .049 model airplane engine will destroy your quad. Hard to beat 29,000 rpms.

curses, Phraglogic foiled again!!