7.4L Mag MPI RPM / MPH - prop slip? 23p

[dcg9381]

I've got a 1998 Glastron CSX-23. New boat to me.
It's got a Bravo out drive. I don't know the ratio.
23.3 feet. I believe it's 3800 lbs.
It's got a 385hp 7.4L (454) Mag MPI motor, which seems to run great.
I believe this boat should hit 65-68, properly propped.
I bought it was another prop on it and the previous owner told me that the speedometer was off.
I swapped the "speed" prop - which I believe is original (not 100% sure) - 23pitch Mercury Mirage prop, stainless, 14-5/8"x23:

http://lakebox.dnsalias.com/photos/1998csx23/mercmarineprop.jpg


I'm hitting 5200 RPM, which I believe is the end of the operating range for this motor.
Speedo reads 50-52mph.
I double checked it with GPS and it's spot on.


Is a 14-5/8x23p prop correct for this application?
Any other suggestions?

 

[CharlieB]

Re: 7.4L Mag MPI RPM / MPH - prop slip? 23p

Are you bragging or complaining?

Unless a rev limiter is holding your RPM at that point then that's all you're going to get.

Try another prop with more blade area or more pitch and see what effect it has, more blade area should reduce prop slip and increase speed, more pitch should also, either should have the effect of reducing RPM tellilng you that the prop you have now is very close to ideal. If RPM remains the same then you need to increas prop even more as the rev limiter is kicking in.

 

[Tail_Gunner]

Re: 7.4L Mag MPI RPM / MPH - prop slip? 23p

I've got a 1998 Glastron CSX-23. New boat to me.
It's got a Bravo out drive. I don't know the ratio.
23.3 feet. I believe it's 3800 lbs.
It's got a 385hp 7.4L (454) Mag MPI motor, which seems to run great.
I believe this boat should hit 65-68, properly propped.
I bought it was another prop on it and the previous owner told me that the speedometer was off.
I swapped the "speed" prop - which I believe is original (not 100% sure) - 23pitch Mercury Mirage prop, stainless, 14-5/8"x23:

http://lakebox.dnsalias.com/photos/1998csx23/mercmarineprop.jpg


I'm hitting 5200 RPM, which I believe is the end of the operating range for this motor.
Speedo reads 50-52mph.
I double checked it with GPS and it's spot on.


Is a 14-5/8x23p prop correct for this application?
Any other suggestions?

Double post.......dont you like the direction your first post is heading...