Mercury 70

[7500Blizzard]

Not saying this motor doesn't have its problems. But how is 2 carbsand cages any worse than 2 carbsand cages for a 4cyl or 3and 3 for a six?

[Mark75H]

I never said it was worse on the triple.

Its the choke point for all of those motors; the triple has a way around it, but has its other issues which I think are mostly related to being a big bore deflector motor. With the blind bore non-removable heads, deflector pistons and internal reed cages none of them are ripe for hot rodding

[Roy Hodges]

I never said it was worse on the triple.

Its the choke point for all of those motors; the triple has a way around it, but has its other issues which I think are mostly related to being a big bore deflector motor. With the blind bore non-removable heads, deflector pistons and internal reed cages none of them are ripe for hot rodding

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Well,............ your S I X cylinder has non removable heads, deflector pistons and internal reed cages ,also .

[Mark75H]

Well,............ your S I X cylinder has non removable heads, deflector pistons and internal reed cages ,also .

Yep makes it a real pain to make much more power than came out of the box. If you had a shop do the work I've done to increase the power from 60 to 88 hp, it would probably cost $4,000. You can usually buy a pretty good used 100 hp motor for $4,000. You could certainly buy a used OMC triple, soup it up some and have cash left over.

Anyone know where I can find 2 more sets of these?

[Plan-b]

Mark75H,

Going form 60 to 88hp is something like a 47% gain that’s not too shabby at all... I was thinking around a 15-25% gain in power form this motor would be more then enough.

As it stands now the motor is in really good shape so I would like to keep it that way... So I would like to know how to keep the top hole form burning up? Do you know the part number for the retrofit kit?

What year and model 3cyl OMC is the best to mod?

Thanks

[Mark75H]

I think the only way you will see any gain with the Merc triple is to put the 3 carb front on it ... but that basically involves finding one ... most likely on a complete "650XS" motor ... so you'd just be trading


The 75 hp 49 ci and 70 hp 56 ci OMC's overlap from 86 to 88, so any triple after 88 is going to be a 56. Before '86 all you need to look for is a 75hp. The short shaft "Stinger" and "Hustler" models have a special skinnier gear case with faster gears. That's where I'd start. Probably a 75hp Hustler, since most people seem to be willing to pay a lot more for the orange paint on the Stinger.

You could go the 56ci route if you'd rather look for newer motors and more cubic inches to start with.

For $1,000 Ed Runne will put on his custom exhaust that made the 850cc Mod class jump from 85 mph to 95 mph overnight on the 49ci motors with stock carbs ... but I don't know how well it fits under the stock cover or if anyone has even tried putting a cover over one.

The top end steam vent is just drill a hole in the top of the water jacket, tap for 1/8" pipe and screw in a fitting to drain away the water, route it down to the bottom cowl and out. Pretty low tech; after people saw what was in the kit they stopped buying them and just made them. If its still running it might have it already

[Mark75H]

The reason I did the stuff to my poorly designed for hot rodding motor is to conform to 850cc Mod racing rules. If I wasn't restricted by the rules, I would have just bought the biggest motor that would float on the back of my boat.