Westernlife
Member
I have a 1977 or so Johnson 85hp V4 on my 1980's 16ft fibreglass Thundercraft, after blowing a bottom end on my 1977 Johnson 70hp recently I switched to this motor because I had it already, the old 70Hp I was able to get with just me in the boat and the gear 55kmh top speed with a 14x17 Prop. Now when I switched to the 85 I figured 15 more hp= worse mpg better holeshot and better top speed... Well not exactly... Holeshot and corner power are a little better, mpg is a little worse but top speed is alot worse... With just me and the gear it gets 47-50kmh max...
Currently it's running I believe a 13-3/4x15 prop, (can't check rpm don't have a tach on the boat) but it sounds about 5,500 it sounds about the same as the old 70, I was told by several people at the local boat shop that the reason I'm slower is the style of prop (forget exactly what they called it but it's straight cut at the ends) and size/pitch, they said to try a 14x17, so I put the 70hp prop on expecting to atleast be back to what I had with the 70... Nope, pretty sure the holeshot was worse then the old 70 and slower top speed, best I could get was 44-45kmh... And I lost alot of RPM, How do I atleast get my top end back? Preferably if I'm burning more fuel and have 15 more horses actually gain top speed... I would love to get around 60kmh if possible.
Picture of the boat is with the old 70hp
Currently it's running I believe a 13-3/4x15 prop, (can't check rpm don't have a tach on the boat) but it sounds about 5,500 it sounds about the same as the old 70, I was told by several people at the local boat shop that the reason I'm slower is the style of prop (forget exactly what they called it but it's straight cut at the ends) and size/pitch, they said to try a 14x17, so I put the 70hp prop on expecting to atleast be back to what I had with the 70... Nope, pretty sure the holeshot was worse then the old 70 and slower top speed, best I could get was 44-45kmh... And I lost alot of RPM, How do I atleast get my top end back? Preferably if I'm burning more fuel and have 15 more horses actually gain top speed... I would love to get around 60kmh if possible.
Picture of the boat is with the old 70hp
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