Re: Prop for 1978 johnson
Not an expert but:
It would be better if we had a better description and size of your boat.Also it is important to know what your present max rpm and speed is. Its important to know how you use your boat,typical load sports etc.
Before getting a prop you should be sure your motor is properly tuned and has good compression.About 100 psi.Also proper set up.The antivent plate should be approximately even with the bottom of the boat.
If you can raise the motor 1 inch without ventilation problems you could gain 2 to 3 mph.
Generally speaking a 4 blade prop is used for low end
performace and will usually be a little slower at top speed
so depending on your present rpm a simple change to a 3 blade prop might be in order.
