Originally Posted by
Fishermanjm
ok i finally got around to gettin the info on my drive,,, 1.65 ratio and a 25 mirage plus i seem to get 60mph on the water pick-up speedo and 4400 to maybe 4600 on the rpm's how does that sound? 6.2l engine
I don't know what speed you should expect with that boat/engine/drive/prop. But to your point about whether it is giving you the right performance, the first question is how fast is it really going now.
Of course if possible, I'd grab a handheld GPS to get a firmer number there. And because the GPS will save your highest speed without you having to watch it like a hawk, it will free you up to play with trim and get a more clear reading off the tach, to see your real peak RPM.
That said, maybe these numbers will act as a bit of a sanity check on the existing pitot speedo's 60 mph reading.
With 1.65 drive ratio, 25" pitch, 4500 RPM:
60.0 mph ---> 7% slip
59.4 mph ---> 8% slip
58.8 mph ---> 9% slip
58.1 mph ---> 10% slip
57.5 mph ---> 11% slip
56.8 mph ---> 12% slip
56.2 mph ---> 13% slip
55.5 mph ---> 14% slip
Not sure if 7% slip is likely to be accurate, but maybe. Seems like about the lowest slip numbers I've ever heard claimed for a "normalish" Classic were down in the 7-8% range, but I'm stretching my memory on that.
Steve (Osur866) and some others have probably measured this stuff very closely.
I don't know what speed your setup should make, and won't even guess. But maybe the slip #s will give some folks here an idea whether the speedo reading is accurate or not.
"I don't have time to get into it, but he went through a lot." -Pulp Fiction