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These numbers are true but don't add up. I have a 454-EFI Bravo 1 which I think is a 1.5 ratio but I'm not sure. The Prop is a 25-P Mirage Plus to Accelerator conversion from Houston Prop. I'm getting 73.5 at 4500 RPM. As I plug in the numbers to an online prop calculator the results don't make sense to what this boat is running.

Thanks
Roby

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Maybe the drive ratio is really 1.36:1?
-Steve

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You probably have a 1.36, however your tach seems low even for that. Your numbers equal 6 percent slip. Check your tach against a diagnostic tach.

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I also guess a 1.36 ratio. Are you sure your tach is accurate? The other variable is your reworked prop may not be performing like a stock 25P Mirage. If you are at 4500 RPM and the speed is 73.5 MPH, then your Mirage is working more like a 26P ( 10% slip).

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The prop works awesome and has cured all of the blow-out problems I had with the stock Mirage plus. The speedo runs dead on with the GPS until I trim up, then the speedo loses a couple of points on the GPS. I will double check the tach. When I plugged in the numbers in a different order I came up with a 1.33 ratio. Now I really suspect that it is the 1.36 you mention. I'm an engine guy not a drive guy... Yet. I will figure out these drives though.

Roby

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Roby, What numbers did you get with a stock prop? Did the numbers made sense for a 1.5 ratio Bravo before the change to the modified Mirage? Doug

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I bought the 25-p prop and took it straight to Houston Prop for modification. I was running a 21-p mirage plus that was a little rough around the edges. It would get about 60 at 4800 RPMs but that was speedo indicated. I didn't have a GPS then.'

Roby

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Actually now that I think about it the RPMs were a little closer to 5K maybe 4900. with the 21-p but the speedo did show 60. but even still it doesn't add up w/o a HUGE margin of error for a 1.5 Thing it though why would someone put a new 1.36 drive in a single engined 22' Scarab? That is the part that REALLY doesn't make sense.

Roby