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View Full Version : Help! Need More Speed!



scottyp
07-22-2009, 01:27 PM
I recently acquired a 1980 18' Classic. The boat has a 2003, 350 small block, 330 HP, Chevy Vortec engine maximized by Indmar, stock thru the hull exhaust. Also a 2003 Alpha one outdrive with a 1:47 gear ratio, with a 14 3/4 x 21' Solas 3-blade prop. Last Saturday I GPS the speed at just under 58 MPH. I feel the boat should run faster. What direction should I go with the prop to increase speed. Running right around 4800 RPM's right now. Thinking about dropping a set of headers on her over the winter and increaseing the exhaust diamater if I think it will help with the top end.

BlownCrewCab
07-22-2009, 01:52 PM
Good exhaust will help some, I don't think your going to turn much more prop (although I think you should spin a 23" prop 4800 with your setup) The right prop can get you several mph, keep trying.

mrfixxall
07-22-2009, 02:06 PM
I recently acquired a 1980 18' Classic. The boat has a 2003, 350 small block, 330 HP, Chevy Vortec engine maximized by Indmar, stock thru the hull exhaust. Also a 2003 Alpha one outdrive with a 1:47 gear ratio, with a 14 3/4 x 21' Solas 3-blade prop. Last Saturday I GPS the speed at just under 58 MPH. I feel the boat should run faster. What direction should I go with the prop to increase speed. Running right around 4800 RPM's right now. Thinking about dropping a set of headers on her over the winter and increaseing the exhaust diamater if I think it will help with the top end.


With 330 hp and a 21 p prop that boat should be bouncing off the rev limiter:)
make sure your timing is rite and its fireing on all 8 cylinders..

BTW welcome aboard!

smbarcelow
07-22-2009, 02:27 PM
...make sure your timing is rite and its fireing on all 8 cylinders..

Ditto. When I brought my boat home, timing was 4 degrees retarded and I reset it to 12 degrees advanced at baseline. After doing that, I would top out at 4,900 RPM's with the trim in the middle setting. At the end of last season, I finally figured out what was causing a misfire I had been chasing. The alternator bracket was interfering with the cylinder 1 spark plug wire and preventing it from snapping onto the plug. Spark jumping to the head had burned a whole through the boot. Once I made enough clearance for the (new) wire to snap on, the difference was night and day. The engine will spin well past 6,000 if I let it. I knew I had a misfire but it sure didn't feel like a dead cylinder.

MOP
07-22-2009, 04:05 PM
Ditto a well setup 300 will do 65 maybe a tad more in the right hands, that 330HP make sticker HP and not real HP.