1970 Mercury Thunderbolt 650cc 65hp 4 cylinder is it really 65hp?

[y2jericho]

I heard motors back in the days where under-rated. So a 100hp would be more like 125 is this true? or is it the opposite. What would my 65hp really be rated <br /><br />I have 73 De Havilland fibreglass boat. Its very light (3 people flipped it over and 2 can carry it (barely) It has the above motor fitted. What would be the approximate top speed? Someone had told me about 85km/h on ok waters and about 100km/h on very carm<br /><br />thanks again The always reliable iboat<br /><br />Thanks!

 

[steelespike]

Re: 1970 Mercury Thunderbolt 650cc 65hp 4 cylinder is it really 65hp?

Motors before approximately 84 were rated at the power head and after at the prop.So before 84<br /> A 65 hp would be less than 65 at the prop say<br /> something like 60 or so.<br />Couldnt tell you speed in km But 50 mph.<br /> would sure be a possibility.Dead calm water might be slightly slower than water with just enough waves to break the boat loose.Weight distribution, shape of the bottom,motor height a trim, type of prop can all effect speed.

 

[rickdb1boat]

Re: 1970 Mercury Thunderbolt 650cc 65hp 4 cylinder is it really 65hp?

y2jericho,<br />I had a '67 650 65 HP on a 15' Wellcraft fiberglass deep V and it ran a little over 40 MPH. But it was surly heavier than your De Havilland boat, as there is no way 3 guys could have lifted mine, much less carry it around. So I also think you should be capable of 50 MPH or so with your set-up. Good little motors, too.

 

[Rex]

Re: 1970 Mercury Thunderbolt 650cc 65hp 4 cylinder is it really 65hp?

Check your ser # to see if it is one that was<br />set 5 degree slow on timing.<br />It's in the book.<br />Rex