Engine RPM/Prop pitch

[hybris1]

I recently installed a new carbureted vortec 350 on my 2700 SCR. It has a Bravo 2 outdrive. At 3400 RPM it runs at only about 18mph. Full throttle, it gets on a good plane at about 25-30 mph at 4200 RPM. According to the engine manual, max cruise rpm is 4000 and max rpm is 5000. I pulled my prop and am planning to have 2" of pitch removed that should give me about a 500 increase. My hope is that it will cruise in a better part of the power curve for the engine. I obviously don't want to cruise at WOT. I am hopping that it is just bogging down the engine too much since my new engine has a much higher RPM range. The prop shop said 2" is the most pitch they can remove. Any suggestions would be appreciated.

[seapuppy]

taking 2" out of the prop will increase your WOT and lower your cruise speed....you want to add 2" of pitch which will lower your wot and raise your cruise speed....

IF I read your post correctly...the main thing is that WOT should be about 5k rpm.....that should be just before the hi rpm cutout engages.....

so...run the boat wot and see where she settles down at..then go from there...your boat should max out at about 42mph...5k rpm....

SP

[hybris1]

My boat maxes out at about 4200 RPM and less than 30 mph wide open. I think the motor may be over loaded since it has a higher RPM range than the old 1998 350 (5.7L). The 350 may be a little small for my boat but I figured a 60 HP boost from the OEM engine would help. My new vortec 5.7L is rated at 300hp at 5k RPM. The OEM engine blew shortly after I purchased the boat. From what I remember of my sea trial, the cruise was close to 25 mph.

[seapuppy]

well..I'd then reduce pitch by a couple inches..or see if you can borrow some props...try them out...see how it works....some prop shops will let you try a few props for a credit card number and then when you decide what prop works...you get to buy it...then save the old one as a spare..


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