How much faster is 90hp more

[benzurin]

Just repowered my 20' 94 Bayliner capri BR with a 350 Mag in place of the 4.3lx 180hp. Haven't taken it out in the water but sounds great with muffs. Out drive is 1.50 with 21p ss. Also the dogbox lid is snug do I need the merc cover over the carb? Hoping to give it as much clearance as I can get but the high rise manifold makes it tight.

 

[benzurin]

Re: How much faster is 90hp more

Maybe a lo pro flame arrester?

 

[QC]

Re: How much faster is 90hp more

How fast did the boat run before? My guess is 10 - 12 MPH, but maybe more. I thought the 350 Mags were 300 php? Is that the same prop as before? Same ratio in the drive?

 

[crazy charlie]

Re: How much faster is 90hp more

Sounds like that baby is gonna boogie!!!I would expect a huge difference.I would expect you will have to experiment to find the "right" prop.

 

[DHPMARINE]

Re: How much faster is 90hp more

Merc cover is not needed,but flame arrestor certainly is a must.You may also want to raise the dogbox for better air flow.Sounds like a good improvement otherwise.<br /><br />DHP

 

[vipzach]

Re: How much faster is 90hp more

Dude, that thing will be like a gazillion miles per hour faster! <br />Seriously, a think you are looking at between 10-15 mph faster. It will depend on the prop and the drive ratio, like QC already asked.<br />DHP is right, you really need that flame arrestor on there! As far as the air flow, try it with the dog box on and off, see what the difference is.

 

[Bondo]

Re: How much faster is 90hp more

Ayuh,......... Like everybody has already said,........<br /><br />You'll see a Noticeable Difference .............. <br /><br />The Flame Arrester is Mandatory,......... The Plastic Mercruiser Cover Isn't..........

 

[Mischief Managed]

Re: How much faster is 90hp more

Heres the way to calculate it: <br /><br />Drag is a fucntion of the square of speed so take your old top speed, square it, then divide by the old HP. Take that number, multiply it by the new HP and then find the square root of the result.<br /><br /> For instance:<br /><br /> 50 MPH top speed with 210 HP changing to 300 HP would be: <br /><br />50 squared=2500, 2500/210 = 11.904761, 11.904761*300=3571.4283, The square root of 3571.4283=59.7614<br /><br />The new top speed would be 59.7614 MPH assuming the new prop is exactly as efficient as the old prop and that the two engines were both accurately rated for power.