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Looking for fresh 49 mercury twin carb powerhead
https://hpbc.ca/viewtopic.php?f=37&t=4397		 Page 1 of 1
Author:  Hounddog [ June 9th, 2022, 8:00 pm ]
Post subject:  Looking for fresh 49 mercury twin carb powerhead
WANTED: Low hour high compression 140 to 145 lbs. three cylinder 49 cubic inch twin carb.
Later models had low dome pistons and approximately 120 lbs compression. Not interested in the complete motor. Long block is an option or even a short block if owner want to keep the intake portion.
Author:  Hounddog [ June 15th, 2022, 12:57 pm ]
Post subject:  Re: Looking for fresh 49 mercury twin carb powerhead
I have educated a few people since I did this thread.
The mid to late 1970’s version of this motor was called the 700.
The early version was the 650
The later version was the 50 and 60 hp...they are horsepower rated at the prop
The 650 is 65 hp at the crank.
The 700 is 70 hp at the crank.
A rebuild spec 700 will likely be 66 to 67 hp at the prop.
That’s 6 to 7 more than the later 60 hp model.
The spec SST 45 OMC running and dominating T750 is approximately the same horsepower.

The 49 mercury is a terrible design compared to the 45 OMC.
It doesn’t have the torque or the upper rpm to match the omc .
But, no one has raced a good 700 on a boat that comes close to T750 minimum weight.

Before 1975 when the 75 stinger/nitro case appeared, the mercury 650 was the better motor in EP. Those boats ran low 60 mph .
It would be nice to see more mercury motors in the T750.
One big difference in running the mercury....11 inch diameter props with the 1:64 ratio gearcase...Much easier to drive compared to the omc.

As for the 3 cylinder Nissan or Tohatsu 50 hp. The 1990 ish “50D” is the best one. It actually is approximately 55 hp out of the box. Problem is blueprinting to UIM spec only gets it to 60 .hp. Yamaha Pro 50 needs a lot of work to compete against a stock 50D. That was confirmed years ago when Hydro Tec wanted to promote the 50 hp Yamaha in APBA class Formula 50 only to find out that the 50D Tohatsu was the better motor.
Author:  Hounddog [ June 20th, 2022, 1:53 pm ]
Post subject:  Re: Looking for fresh 49 mercury twin carb powerhead
I haven’t had any success so far finding exactly what I was looking for. I knew it was a long shot. The only resent one I knew of was a 650XS front end on a stock block. I did find an empty 700 block I had saved after using the crank, rods and pistons in a 650XS after new pistons were not available from mercury. Back then there was only one oversized piston 15 over That 700 had the 15 over pistons. In late 1995 there was a CBF rule change that allowed aftermarket pistons in the 650XS. A group of us did a one time order with wisco for std. and 30 over non powerport pistons .Powerport pistons cause blow by in an XS.

So by chance does anyone have 15 over original high dome non powerport mercury pistons or even better 30 over wisco?

FOUND oldmercs.com has original .015 1977 to 1979 mercury 700 pistons...$125.00 us each.Comes to approximately $450.00 US with shipping. Add tariffs if any, taxes 75 cent Canadian dollar.....total makes this option too costly.
Author:  Hounddog [ June 27th, 2022, 8:10 am ]
Post subject:  Re: Looking for fresh 49 mercury twin carb powerhead
Got one!! It is either a totally fresh rebuild that was never fired up 30 years ago or less likely NOS. I won’t know if it’s a 120 or 145 compression powerhead until I test it. If it is not a 145 compression powerhead I will install the high dome pistons.......sometimes you get lucky!
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