86 sylvan 2.5 HO motor upgrade

by Dave dmesenbrink@nwrecc.org
(Thermopolis, WY)

I have my fathers last boat, an 1986 sylvan 22 ft. runabout with cuddy cabin that has a 2.5 ltr. straight 4- cylinder chevy motor to push it. It is in great shape, new paint, rebuilt Cobra I/O, rebuilt Rochester 2 bbl. and new GM 4 cyl. motor. In my manuals it mentions a 2.5 HO unit. Was a 4 bbl. carb added to increase HP output? I live at 5000+ altitude and power is noticeably less than 1100 ft. I would like to gain back most of the lost HP and am having some difficulty finding information and specs to do that. Motor runs on a cupful of gas while trolling,but difficult to go more than 30 mph on plane. RPM @4000- 4200 WOT , prop is now a 15 pitch to get on plane quickly and help RPM's. I am hoping this can be done for spring season.

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