Prop selection for (39)89 2655 to reach correct rpm at WOT-gctid394019

[Guest]

Took my boat out today for the first successful trip. I've got about 4 hours into my new engine break in. (Michigan Motorz 5.7 260HP). The engine is topping out at 3200-3400 rpms. I have a Cobra Outdrive (not sure of the ratio) and a 15x15.5 prop. Can anyone tell me the proper prop to reach the specified WOT rpm? Do I need to give more info, if so, please let me know. Oh, my boat is an 89 2655.

Thanks,

Greg

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wefivehodges wrote:
Took my boat out today for the first successful trip. I've got about 4 hours into my new engine break in. (Michigan Motorz 5.7 260HP). The engine is topping out at 3200-3400 rpms. I have a Cobra Outdrive (not sure of the ratio) and a 15x15.5 prop. Can anyone tell me the proper prop to reach the specified WOT rpm? Do I need to give more info, if so, please let me know. Oh, my boat is an 89 2655.

Thanks,

Greg

Sounds about right. Time to check the outdrive ratio.

[Guest]

What speed are you going at that 3400 rpms? You should be able to get up to 4500 rpms. If it won't go above 3400 that would indicate severe "lugging" The 15" pitch prop sounds about right. Are you sure your automatic spark advance is working?

Don

[2850Bounty]

Greg, if those are your WOT RPM numbers, you are severely over-propped, or your engine is not tuned correctly!

If over-propped, DO NOT do your break-in propped liked this!

I don't mean to chew on you, but all of this should have been taken care of prior to any new engine break-in!

If anything, you'd want to be slightly under-propped!

Which ignition system do you have, and how have you set it up for TA?

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