dyno...i don't understand...your running 23's @5100@ 75mph...that's making water out the other side...even with 1.36's that's a very respectable loss of <10%....

GO4 if your prop was not labed for YOUR boat i see how that could happen...my guess is that metal was removed incorrectly for the weight, X-dem, and D-rise of your boat...resulting in unwanted blade flex for your application....thus what you made up in thinner more hydrodynamicly correct blade design you lost due to the real world conditions you put it in.

Dyno, I don;t get your numbers either. Unless you are running 1.36 gears..but even then that means only about 10% slip as Audacity said.

I have 98 31 ss with 454 mag mpi's, 26p. I calculate my slip at 13%. My top end is 68 at 4800 rpm's.

Dont know what to tell you guys I just put the hammer down and read the tach and the GPS.....

forward progress can only come if you have good data!

Dyno,

I have a 1990 with a pair of 640s running low to mid 90's on a perfect day. 85+ consistantly. It takes some choppy water to get her moving! When the boat leaves the water at high speeds you can feel it lunge forward. So lots of trim and 2-3' chop and she screams.

I am also confused. I don't know how you can see 74-75mph with 23 props.

Audacity- you're probably right, it was supposedly done for my boat, but it was cheap so I don't complain. At least they look good!
Dyno, see if you can try to get you hands on some 25 mirages and see what that does. Those 23's seem awfully small, have they been tweaked?

Goforbroke not as far as I know......they came on the boat...
Ken thanks for the info thats more the infomation I was looking for......guess I should learn to read a tach and a GPS......

dyno, if you happy with what you got then cool...but if you want more?,,, then you need to base line and take good data that is repeatable...i will be more than happy to set ya up on the right track...feel free to email or phone! take care...

Dyno, sounds like we need to take my Snap On timing light w/ built in digital tach and verify your tachs next spring. Mine was off by 600 rpm when I bought my boat and 300 off this summer again. What kind of gauges do you have? I don't know anything about slip or that stuff so if your gps is reading 75 sounds like either your tachs are off or your props have been changed from their stamping. Marysville in Grandville can measure your props for you.