Low RPM's prop to large?

[salTnuts]

First let me thank everyone for their time helping me out. I am new to the forum and look forward to contributing in the future.

I have a 1989 Chris Craft 245 Limited with a 454 freshly rebuilt with about 20 hrs on it. The motor has been bored .30 over with a performer intake and a little head work and mild cam. Stock hp on the engine is 335 and I am pretty sure that it hasn?t changed much with my mods. The boat weighs about 3300lbs dry. It has a Bravo one out drive. My problem is I am not getting over 3800 RPM WOT out of the engine. I have aligned the outdrive and motor so no binding. I suspect the prop is the problem. I still have the prop that came with the boat it is a Merc Mirage plus 15.5 x17 SS. Was told this is way to big for the outdrive/engine and will possibly damage both. I ran it last year 2 times and broke the clutch shaft and had to replace it. I am looking for your thoughts and input on my situation and any suggestions on a new prop.


Thanks

 

[QC]

Re: Low RPM's prop to large?

Can you get us your speed (GPS) and drive ratio? At first glance I think your tach is off, but I always say that . . . 17 inch pitch should not be an issue regardless of the 15.5 diameter. Also, dry weight on a 19 year old boat is pretty meaningless. She could be waterlogged.

Let's see if we can make sense out of your numbers first. I'm going to move this over to prop topics although I am not sure that is where you belong yet. Could be engine, could be hull, could be prop, could be bad data, could be all of the above at this point . . . Good luck, we'll be patient if you will, and hopefully get this nailed down.

Edit: Oh, oops, welcome aboard!!!

 

[FreeBeeTony]

Re: Low RPM's prop to large?

Not an expert but I certainly doubt that prop is too big for a BBC.

What is the ratio of the drive?

 

[dontask]

Re: Low RPM's prop to large?

Why don't you find out what prop design (pitch & diameter) it originally came with from the manufacture and work from there? Some manufactures will respond. If you bought the boat used, the prop that came with the deal could have been the wrong design too.

 

[crxess]

Re: Low RPM's prop to large?

No way your prop is causing the low rpm's

Double check you engine setup. I have found, more times than not. Crossing 2 plug wires will cause the motor to run flat(weak) while not causing a backfire. I have seen this more times than you would imagine.

My SeaRay 225 Express @ 5800lbs. Worn out 305 turned 5600 rpm. prop 14.5x17p