How does engine cc impact performance?

[Foz240]

Hi all

I have a 2009 mercury 20hp on a Lund WC14 DLX . I am debating upgrading to a brand new mercury 25hp.

The 20 is a 333cc, the 25 is 500cc. I realize this is only a 5hp gain (25% increase) but it’s even more of an engine size increase (50% increase). How does the engine size increase impact performance? Does this equate to much more torque than the 20?

Note: I typically run the boat fully loaded, or occasionally pull one of my small kids on a tube. I have tried an adult in the tube and although the boat does get on plane, it definitely struggles to do so with an adult.

Thanks!

 

[FuzzyGrub]

Yes, in general, more displacement equals more torque. Torque is most important to geting on plane. Unfortunatly, mfgs don't publish torque curves. 50% more displacement should equal a torque difference that you would feel. If you upgrading, might consider even larger, as long as your boat can handle it.

 

[Foz240]

Yes, in general, more displacement equals more torque. Torque is most important to geting on plane. Unfortunatly, mfgs don't publish torque curves. 50% more displacement should equal a torque difference that you would feel. If you upgrading, might consider even larger, as long as your boat can handle it.

Appreciate the reply. My boats plate states a max of 25hp….

 

[Weldorthemagnificent]

Be a bit more jam but at a weight penalty. Tubing is hard on a boat and if that's the goal, maybe need to upgrade the whole package. The Mercatsu 20 is a good motor, an overachiever imo. Maybe you can play with motor height and weight distribution to get a better running boat. Check rpms and see if a prop change may be the ticket. Still ain't gonna pull a tube. Now a knee board is another option. I pulled one easily with an old 14 tinner and a 20 johnnyrude.

 

[Foz240]

Be a bit more jam but at a weight penalty. Tubing is hard on a boat and if that's the goal, maybe need to upgrade the whole package. The Mercatsu 20 is a good motor, an overachiever imo. Maybe you can play with motor height and weight distribution to get a better running boat. Check rpms and see if a prop change may be the ticket. Still ain't gonna pull a tube. Now a knee board is another option. I pulled one easily with an old 14 tinner and a 20 johnnyrude.

Thanks for the reply. I have a 9 pitch prop and it just about maxes the rpm with the boat weighed down so I think I’m good there. Have also played around with trim.

The new mercs are surprisingly lite, I think I’ll only be adding about 20#.

Noted on the whole upgrade package. I’m limited on boat size due to garage.

 

[thill]

You might want to try a couple of different props, maybe a 10 or 11 pitch. Prop design can make a big difference. There are so many to choose from. Your local marina may have some suggestions, and often they will let you try before you buy, as long as you don't damage them.

 

[Foz240]

You might want to try a couple of different props, maybe a 10 or 11 pitch. Prop design can make a big difference. There are so many to choose from. Your local marina may have some suggestions, and often they will let you try before you buy, as long as you don't damage them.

Thanks. Wouldn’t going higher in pitch make it even harder for the boat to get up on plane? I’m running a 9 now…

 

[sonny.barile]

Thanks. Wouldn’t going higher in pitch make it even harder for the boat to get up on plane? I’m running a 9 now…

Yes……the higher pitch can add top end but slows acceleration and may stop you from achieving hole shot.
When pulling tubes or skis you want to lower pitch to keep rpm’s up and be able to plane with the added weight.

 

[flatheadsteve]

I don't know that going up to a 25hp from the 20hp you have now would give you what your looking for. Tubing creates a lot of drag especially when the tube catches a wake wrong and nose dives under the surface.