How much faster??????

[Bull54]

I have a j16 Carolina Skiff, it had a 1985 35 hp Mercury on it and I am changing that out and putting a 1988 40hp Mercury on it, this is a 4 cylinder, I think it is the old Mercury 50hp. I am wondering how much faster it will push my boat compared to the 2 cylinder 35 hp? The 35hp pushed me around 27mph.

Also I have 2-6 gallon fuel tanks, and I am wondering if it will use so much more gas that I should maybe get an 18 gallon tank, but will that add too much weight for the motor to push?g?

ALso ahve an 11.1 X 13 aluminum prop. Would this be okay to use on it or should i get a different size for better handling?

Thanks in advance or the replies.

 

[Bull54]

Re: How much faster??????

no interest?

 

[mike1245]

Re: How much faster??????

dont think it will be much differance

 

[Barnacle_Bill]

Re: How much faster??????

You might see 30 MPH. The 2 tanks you have are plenty. AS
for the prop we need to know how many RPMs you turn at WOT to give you a good answer.

 

[Moody Blue]

Re: How much faster??????

Not likely to see a noticeable difference in speed. Maybe 1-2 MPH. As for fuel consumption, rule of thumb is consumption equals 1/10 of rated HP at WOT. So theoretically your consumption at WOT will change from 3.5 gal/hr to 4 gal/hr, again not a noticeable difference.

 

[Bull54]

Re: How much faster??????

Thanks guys.

 

[Bull54]

Re: How much faster??????

Well seems my mechanic and I had a meltdown in communication

It says on the side of the motor "Classic Fifty", on the front facing of the motor it says "45 Power Trim". I asked my mechanic about that, and he stated it was originally the 50 HP but when they changed how they rate the motors from the head to now the foot, it lost 5 HP so Mercury called it the 45 HP. But it is the original 50hp mercury had.

So can I repeat my question? How much of difference will this make now?

 

[mike1245]

Re: How much faster??????

might make a little but depends on price of motor if its worth it or not

 

[achris]

Re: How much faster??????

Just as a comparison, I changed from a 180hp engine to a 220hp engine and went from 40 knots to 43 knots.... Not a lot of difference (not even 10%).

You might pick up 3mph.... Fuel consumption should be about the same... To push a boat at x mph will require y horsepower. Y horsepower will need z gals/hr and, within reason, it doesn't matter what size engine you use to produce that, it will require the same amount of fuel...

Chris........

 

[wellsc1]

Re: How much faster??????

Give some attention to the prop. Make sure the diameter will fit the lower unit of the replacement motor. The prop may need to be replaced to achieve the proper max RPM at WOT, else harm to the engine may result.

I replace an old Mercury 40 hp (measured at the engine) with a 40 hp Force (by Mercury). The prop on the old 40 was a tad too much pitch, but it worked perfectly on the replacement 40 (the difference was where the hp is measured.

 

[Bull54]

Re: How much faster??????

I only paid $900 with tilt and trim and installed so not too bad in my book.

 

[achris]

Re: How much faster??????

I only paid $900 with tilt and trim and installed so not too bad in my book.

Great!!!

Enjoy PTT....

Chris......