Mercury 115 Pro XS four stroke

[creeljd]

Has anybody on this forum had the opportunity to run the 2.1 liter Mercury 115 Pro XS four stroke?

[ROLF]

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[MeCapnDave]

I just bought one for my Wahoo, I have to rig it yet but will keep you posted when I get it running !

[RSWORDS]

Yep. Great motor

[Tcatrett]

We sell a lot of the new 2.1Ls. Great motor. All customers very happy with power fuel and quiet..
If you have a bigger than 18' heavy hull go with the CT..

[V-bottom]

We sell a lot of the new 2.1Ls. Great motor. All customers very happy with power fuel and quiet..
If you have a bigger than 18' heavy hull go with the CT..

Which motor is better for pontoon- the proxs CT or standard 115 with the CT gearcase. Looks like the pro is another $400 or 500 bucks more and not sure if the performance tuner will be a disadvantage on a pontoon boat?

[Tcatrett]

Which motor is better for pontoon- the proxs CT or standard 115 with the CT gearcase. Looks like the pro is another $400 or 500 bucks more and not sure if the performance tuner will be a disadvantage on a pontoon boat?

Standard 115 CT

[V-bottom]

Ok so I just ordered the standard 115 CT. Going to pick it up on Saturday and get it installed next week. This will be interesting to compare the 115 opti currently on the boat being replaced with the 115 4 stroke. I can share the results once the motor is broken in if y'all are interested.

[RSWORDS]

We swapped a proXS 115 in place of a 115 opti on a job boat a couple years ago. Forget the exact numbers but it performed alot better. It liked the enertia prop.

[kah68]

Ok so I just ordered the standard 115 CT. Going to pick it up on Saturday and get it installed next week. This will be interesting to compare the 115 opti currently on the boat being replaced with the 115 4 stroke. I can share the results once the motor is broken in if y'all are interested.

I'm interested Doug, I was thinking it would be an upgrade to the 90 Yam on my deck boat lol

[V-bottom]

Ok so I just ordered the standard 115 CT. Going to pick it up on Saturday and get it installed next week. This will be interesting to compare the 115 opti currently on the boat being replaced with the 115 4 stroke. I can share the results once the motor is broken in if y'all are interested.

Got the pontoon in the water yesterday. put the same prop (4 blade trophy 17P) on the 4 stroke that was on the opti and the top speed was way less as there was too much slip on the prop. As a fair comparison the 115 opti gear ratio is 2.07 vs 115 CT at 2.38. This should of made a top speed difference of 4 mph using the same 5800 rpm wot. but the wot speed was much less with the 4S. The slip ratio went from 22% to 44%. You could feel the prop slipping. The first thing that came to mind was Wildman's post testing on the new 300R...that they needed way more prop.
So we lowered the motor 2 holes (1.5") to see if that would allow the prop to bite a bit more and I put on a 19 pitch ski prop and the slip numbers improved but still 4 mph slower than the opti.

I really hoped I wouldn't have to go through all the prop testing all over again and just can't understand how or why the same 115 hp motors could run so different on the exact same boat with the exact same prop.
In short, I love how quiet the motor is but it is definitely using way more gas than the opti. I was shocked that we burned at least 30% more gas than the opti doing the same run around the lake. I hope this is just because of the break in period? But more likely from the higher slip numbers. I have to cruise at 3000 rpm with the 4 stroke where I used to cruise at 2000 rpm with the opti. I have been carrying an extra 5 gallon gas as backup so I don't run out. I guess I have to find the right prop to get my slip numbers down and hopefully improve the fuel consumption. I will try to get my hands on the Enertia prop to try as RSWORDS mentioned worked for him.

I will update once I get some more prop testing done... And no I am not buying any 5 blade cnc props for it.

[Tcatrett]

They like big diameter props with no vents. Most pontoons we done like the mirage style 15-19p.

[Tcatrett]

Any prop venting will slow these motors down alot. I seen them loose the plastic hub spacer between prop and housing and slow down 3-4 mph..

[V-bottom]

Ok so I have been doing some more prop testing.
I tried adding the plastic hub spacer on the trophy and it made no difference in the slip. It was only doing 9-10 mph @ 3000 rpm and 15 mph @ 4000 rpm.
I tried a 19 pitch 3 blade apollo stainless prop and a spitfire 19 pitch 4 blade aluminum. They both worked well. 16-17 mph @ 3000, 23 mph @ 4000, 29 @ 5000 and 33-34 @ 5400.
In summary, the motor is exactly the same top speed as the opti, the gas mileage is getting better and it seems to have more punch at any rpm. The most noticeable thing is the 1600-1800 rpm vibration the opti had is gone. The whole damn boat used to vibrate and resonate before. The 4S is definitely quieter and smoother.
I would tend to say it has a better top speed with 4-6 adults but I never did any back to back speed tests before in this scenario.