Cobra1

I have a 28' Cobra with 770 HP. I have a Max drive with 135 gears. I tested two props both 4 blades. The results are as follows. 28 pitch prop @ 4200 RPM (max RPM )ran 80 MPH I then Ran a 26 Pitch and only ran 76 MPH @ 4800 RPM (Max Rpm) This is mind boggling due to the fact i am running a Pro Charger and most of my boost is after 4200 RPM. In addition to all this I think i need moore lift. HELP!!!!!

hillbilly24

I'm sure Throttle up and Bblades will hop in in the morning with some more educated opinions then I but Your numbers don't sound right at all. 770HP in that boat should be able to spin atleast a 26" wheel to more than 4800RPM een with the 1.35 gears, Was the motor tuned on a dyno? I would check some mechanicls before I got too crazy.

Cobra1

Yes! The motor was run on a dyno and Lake testing to dial in the computer. I thought the numbers sounded way off. I am thinking that maybe i am having trouble reaching 5400 RPM due to my coil packs. Maybe thats whats throwing me off. The mystery is that on the dyno we ran 5400 RPM before the cam fell off. Why would that change in the boat? Even if i were running only 700 HP the numbers seem off. I think what i will do is try a really small prop like a 24 and see if I max out at 4700 RPM. Thanks for the reply.

PS: I knew that rebuilding a 496 would be tough, but not this tough.

bbladesprops

Good morning,

Your numbers are kind of goofy. The slips varies 10% between the props. Thats too much.

I suspect engine issues. Can't turn the r's under a load. This affects your performance numbers.

A small prop may or may not produce the issues you experienced with the 28. Dyno may be the next move. I'd look at your same thought........spark.

Good luck.

hillbilly24

Maveric Marine in VanNuys has a prop shaft dyno and can help you get this all figured out. I used to work over there and Eric the owner,and Dan the tech are both ontop of their stuff. Give him a call @818 989 4445 tell him Jake sent you

Cobra1

Thanks so much! Why i ever rebuilt a 496 is beyond me. If it works it will be nice. If any one has ever had luck with a 496 rebuild i would love to talk to them.

hillbilly24

get ahold of Ray with Raylar, I forget what his screen name is on here but he is the man to talk to when it comes to 496's.