Upgrading from 70hp to 90hp

[nim713]

I have a 2000 sylvan expedition 1600. Currently it has a 99 johnson 70hp on it. It's rated for a 75hp but the same model in years before and after are rated for a 90hp. What issues would there be upgrading to a 90hp?

 

[jimmbo]

A 20 hp increase will get you about 4 mph more top end.
I guess there is a Chance that for one Year they made the boat differently and thus the reduced HP Limit. Myself, I have never worried about a slight Overpower. I always made sure the Underwriters of the Insurance, knew it was exceeding the HP recommendation, and that it was on the Policy, and they were still willing to Underwrite it. Where I am, you can put a 200 on a rowboat and no Laws are being Breeched. Other Places may get a little or a lot Anal about though.

 

[jbcurt00]

In some states, overpowering the max hp is considered reckless operation, a ticketable offense, regardless of how diligent you are on the throttle. WV is 1 of those states.

 

[jlh3rd]

that boat is only 16' long
not only does the placard list max hp, it also implies a max motor weight limit.
So a 2 cycle,70 hp johnson weighs 250lbs. A 75 hp 2000 model 2 cycle can't weigh much more.
4 cycle motors weigh more in comparison.
How much does that 90 weigh......just stuff to consider...

 

[nim713]

that boat is only 16' long
not only does the placard list max hp, it also implies a max motor weight limit.
So a 2 cycle,70 hp johnson weighs 250lbs. A 75 hp 2000 model 2 cycle can't weigh much more.
4 cycle motors weigh more in comparison.
How much does that 90 weigh......just stuff to consider...

It's a 2 stroke and the weight is 330lbs

 

[jlh3rd]

..just hard to say what the extra 80 lbs will do..
unusual about just this model year only....

 

[ahicks]

I wouldn't let the 70 get too far out of your sight until you see how that 16' boat looks in the water with a 330 lb 90 on it...... whether it's rated for it or not....

 

[jimmbo]

I will assume the 90 is a V4, as 330lbs is what the later V4 90 weighed. Is it a Crossflow or a Looper?

 

[airshot]

I have a 16' Sylvan side console that is rated for 80 hp...I have a 40 hp 2 stroke on it, 195 lbs....could not imagine a 330 lb motor on the back....when I stand back on the transom (165 lbs) I don't have much freeboard at the transom!! You might stand back there and see how your does....what is wrong with your 70 hp ? I get 31 mph from my 40....

 

[nim713]

I will assume the 90 is a V4, as 330lbs is what the later V4 90 weighed. Is it a Crossflow or a Looper?

It is a 4v but I honestly don't know about looper or crossflow

 

[nim713]

I have a 16' Sylvan side console that is rated for 80 hp...I have a 40 hp 2 stroke on it, 195 lbs....could not imagine a 330 lb motor on the back....when I stand back on the transom (165 lbs) I don't have much freeboard at the transom!! You might stand back there and see how your does....what is wrong with your 70 hp ? I get 31 mph from my 40....

The 70 has been giving me issues and no mechanic has been able to correct it. With the 70 I get around 31mph on glass water. However it's a wide boat. Almost 90 in beam.

 

[jimmbo]

It is a 4v but I honestly don't know about looper or crossflow

Do you have a Picture of it?

 

[airshot]

The 70 has been giving me issues and no mechanic has been able to correct it. With the 70 I get around 31mph on glass water. However it's a wide boat. Almost 90 in beam.

Makes sense...stand on the transom straddling your current motor and see how the extra weight lowers the transom, that will show if the weight would be an issue !
90" beam is a much bigger beam than mine !!

 

[Texasmark]

Wide beam is a big plus. 20", not 15" transom engine mounting height is also a big plus. Moving some weight forward can help to mitigate the extra weight....side console vs tiller steering is another big plus....would think that is how your boat is arranged. If you had a front deck with controls at a front seat a bigger plus. As jimmbo suggested, a few pictures of interior layout and hull shape would help us to help you.

 

[flyingscott]

You are going to add almost 100#s to the transom

 

[jlh3rd]

FWIW...
When I replaced my Merc 60 hp 4 stroke with a 115hp 4 stoke on my 24' pontoon ( which the placard said is max) ...it was noticeable. The pontoon has 25" diameter toons also.....
The bigger issue was the bounce at the transom when trailering....significantly so that I now use a transom saver.....

 

[nim713]

Wide beam is a big plus. 20", not 15" transom engine mounting height is also a big plus. Moving some weight forward can help to mitigate the extra weight....side console vs tiller steering is another big plus....would think that is how your boat is arranged. If you had a front deck with controls at a front seat a bigger plus. As jimmbo suggested, a few pictures of interior layout and hull shape would help us to help you.

Wide beam is a big plus. 20", not 15" transom engine mounting height is also a big plus. Moving some weight forward can help to mitigate the extra weight....side console vs tiller steering is another big plus....would think that is how your boat is arranged. If you had a front deck with controls at a front seat a bigger plus. As jimmbo suggested, a few pictures of interior layout and hull shape would help us to help you.

 

[jimmbo]

Wide beam is a big plus. 20", not 15" transom engine mounting height is also a big plus. Moving some weight forward can help to mitigate the extra weight....side console vs tiller steering is another big plus....would think that is how your boat is arranged. If you had a front deck with controls at a front seat a bigger plus. As jimmbo suggested, a few pictures of interior layout and hull shape would help us to help you.

I was suggesting Pictures of the motor, to determine if it was Crossflow or a Looper

 

[airshot]

View attachment 378918

Wow...that is a wide boat...nice !!

 

[jlh3rd]

yeah..that is a wide boat....certainly looks like it could handle a 90....