Hopefully you guys can help me out here. I was wondering I have a 31' 1979 Excalibur t-454 400hp motors trs drives 23p mirage 3-blade. does anybody know what the RPM range should be for these motors? right now the most I can get out of them is about 4700rpm ??

If they are 400 MCM Cyclone engines then 4800-5200 was the recommended RPM

I would shoot for 5000 to 5200 as long as the engines are healthy. Primary concern being valvetrain.

Dave

these are the original engines in that were in the boat about 800hrs boat sat in a garage for about 10 years
comletely stock never rebuilt. still sound great.

Most likely the rpm is down due to weak valve springs, they will make a very effective rev limiter I`m sure the valves aren`t sealing too well either.


800 hrs, they have had a good life. Time for good old 'look see'

And weak valve springs spells disaster at elevated rpms. Valves won't get enough seat time to cool properly. A valve job with a checking of the springs is minimun to avoid disaster. Also will give a nice chance to service the exhaust system.

Dave