Difference between 2014 Yamaha F8 and F9.9

[oldiron52]

My apologies if this is an old subject, couldn’t figure how to search 1500 pages of posts on the subject. Anyway, what makes the 9.9 1.9 HP greater than the 8.0? I know the displacement, pistons, and rods are all identical. Is it in the lower unit gearing; or prop used? Is it a governor of some sort? Is it in the CDI unit? Maybe the tweaking of the carburetor? Please tell me if my F8 is the same thing as a F9.9, or not…Thanks.

 

[raczekp1]

1. cam on camshaft( in cylinder head) is higher. so valves are opening wither and fuel + air is going into cylinder much more. engin can reach more rpm,
2. 9.9 -main jet has bigger hole to deliver more fuel and carb throat is little wither to get more air

 

[boscoe99]

Are you trying to compare an F8SMHA with an F9.9SMHB? Just saying F8 versus F9.9 is no longer enough. These are the two models that were manufactured in 2014.

Open the Yamaha parts catalog for the F8SMHA. Open the Yamaha parts catalog for the F9.9SMHB.

Then open the same illustration for each model. Compare the part numbers for similar items. Crank shaft to crank shaft. Block to block. Cylinder head to cylinder head. Carburetor to carburetor. Cam shaft to cam shaft.

I am not seeing that the rods and the pistons are the same. As are most of the other parts.

 

[oldiron52]

Thank you for your posts, I now clearly understand the differences in camshafts is what makes the HP difference and the proper parts illustration shows these parts are different from each other.

How about my propeller? Currently it’s an 8.5D x 7.5P which is banged up enough to go ahead and replace it. 8.5D is standard and Pitch is option of 7.0, 7.5, 8.0, and 9.0. I run the short shaft on a 14-foot aluminum boat weighing about 250 lbs. Myself and gear would be an additional 300 lbs. Would a smaller or larger diameter prop of 7.5” get me through the water any quicker?

Any other tweaks I can do on this F8CMSH (2020 not 2014 as first reported) to get a little more RPM out of ur?

Thanks…Scott

 

[Sea Rider]

Before playing with prop pitches need to know the min-max wot rpm range factory stated for that 8 HP motor, install an induction tach, go for a wot run as usually loaded and report max wot rpm achieved. Test it with current prop, will know how much less pitch will need to go for the motor to rev higher, better hole shot and gain bit more top end speed.

If counting already with a 7.5 pitch the only option would be going for the 7.0 one. Diameter is what the prop manufacturer wants to play with and it's relative, pitch is all....

Happy Boating​

 

[boscoe99]

Any other tweaks I can do on this F8CMSH (2020 not 2014 as first reported) to get a little more RPM out of ur?

Thanks…Scott

In what country are you located? Reason why I ask is because here in the US the F8CMSH was last offered in 2010/2011. Long time before 2020.

 

[boscoe99]

My apologies if this is an old subject, couldn’t figure how to search 1500 pages of posts on the subject. Anyway, what makes the 9.9 1.9 HP greater than the 8.0? I know the displacement, pistons, and rods are all identical. Is it in the lower unit gearing; or prop used? Is it a governor of some sort? Is it in the CDI unit? Maybe the tweaking of the carburetor? Please tell me if my F8 is the same thing as a F9.9, or not…Thanks.

From where are you getting your information? A 2010 F8CMSH is very different from a 2010 F9.9FMSH.

 

[boscoe99]

The best that you can do is to prop the motor so that with the boat loaded and the throttle wide open it will run at or near 6000 RPM. Maybe play with the engine mounting height and the trim angle.

 

[oldiron52]

In what country are you located? Reason why I ask is because here in the US the F8CMSH was last offered in 2010/2011. Long time before 2020.

Typo on my part, meant 2010.

 

[oldiron52]

From where are you getting your information? A 2010 F8CMSH is very different from a 2010 F9.9FMSH.

Thanks for the specs! Clearly I was reading the old school stuff. Lesson learned, always start in this forum if you need questions answered correctly.
Again, thanks for all your help and replies.