Rebuilt 6bta 5.9 engines

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I had two rebuilt 6bta 5.9 300 HP engines put into my 380 aft cabin searay last season. I have not been able to reach 2800 rpm’s under load. The engines have been checked without load and are at 3100 rpms. All other components seem to be working okay but I’m at a loss as to why I’m not reaching 2800 under load.
The bottom is clean and I was able to reach 2800 with the engines I replaced. I have four blade props which have not been changed or adjusted since I installed the rebuilts.
The starboard engine is at 2600 under load and the port is 2575.
I’ve checked the throttles to make sure they are reaching the stop wide open and they are.

It seems like a common problem for both but can it be that the props need to be adjusted for these engines even through the engines I took out were exactly the same.?

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[Tony Athens]

If tachs are accurate, then you need to loose a full 3″ of pitch.. 2950 in the number you want to get the field performance” these engine can deliver..

Remember, your boat is not a test cell and the minimum rated 2800 RPM was derived inside a test cell on a dyno…………………My suggestion is to just do it and not question –You’ll thank me later…

Tony

[Bob Neill]

Verify that your tach gauges are correct. For example, my gauges read 2200 rpm and when checked with a laser tachometer they both are running
at 2060 rpms that’s a big difference and that’s across the entire rpm scale! Until you know that the gauges are correct your guessing.

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