Omc Cobra 5.7 prop question
 

Hi all, Im new to this forum and have a question that has obviously been beat to dead but my situations a little different. I haven't graduated to the big boy boats like most of you yet. Im running a 21.5 reinell cuddy. It has a 1:41:1 cobra drive. I just put a set of vortec heads on it with the edelbroc vortec intake and thru hull exhaust. I currently have a 19 prop on it and im curious as to any of your thoughts on if if can handle a 21? Im turning about 5300 or so at wot going about 41 to 45 so it tells me... My guess is the motor is running an honest 280 to 290 horse or so realisticly. Anyways any thoughts or advice would be great. Oh as for what im looking for is a better top speed like to do 50 55 or so and still come out of the hull decent. Right now it launches out of the hole like a v drive with those new mods.

Something seems off. Theoretical speed with that prop/ratio/rpm is 67.6mph. If you are seeing 45, that is 33% slip which is really high. Is your tach accurate? Is the gps speed in MPH or Knots? I had a cobra drive in a stingray turning around 5400-5500 with a 19 pitch stainless prop running low 60s.

If the motor is stock cammed, sounds like it, 4800-5000 would be better, so yeh, it will hndle a 21.

Is your 19" an aluminum or a who know what prop ? As mentioned above, your slip sounds brutal.

Solas Props works pretty well for these apps. Solas makes props for the OEM Volvo SX drives in which years ago OMC Cobra and Volvo were the same drive 1994 thru 1998.

My prop is a ss 19 but im thinking im going to check my speedo when I say it reads 45 mph it is the original speedometer in the boat. and judging by the sound of it at 5300 it does sound like there is slipping happening a bit and not a lot of load on it. I will also check my tach as well and make sure it is accurate. im running the msd marine box and autometer tach run off its tach output and not the negative side of the coil as one would normally do. Oh and the it isn't stock cammed I put a comp cam marine cam in it and I don't remember the lift or duration off hand its been a while. Putting this cam in I regret as idling down low at the docks is a bit difficult 950 is as low as it will stay running