30' cat single hp500 WOT 3500 no more? Need help
 

I have a 30' cobra terminator cat I had just bought it has a hp500 500-540hp it has a bravo 1 1.36 ratio and a 26p bravo prop, at WOT I'm getting between 3500-3800 rpm max @ 55-58mph I'm not sure if I have a timing issue fuel issue or if it needs a 1.50 ratio drive it planes out strong then falls on it's face at 3k rpm

Looking for some help

I am going to swap the 1.36 drive out with a 1.50 this weekend to see what happens

Any help would be appreciated

Wouldn't it be easier to change the prop?

I would certainly check the timing before swapping drives.

With proper slip% and a 1.36 ratio drive and 26" prop it should run about 80mph at 5000rpms.
I don't think your issue is 1.36 ratio. You could drop down in prop pitch. It will have the same effect as swapping to a 1.50.

You don't have enough HP or Torque to spin that prop to 5000 RPM. I have a 26 ( actually 27 ft ) Daytona with 650 HP ( 509 CUBES ) and the 1:34 ratio drive and a labbed 30 Bravo at 5400 RPM.

But saying that - I think there is something wrong with your engine. The fact that it comes out of the hole well and then falls flat tells me something is holding the RPM's down. How far below the lowest point on the bottom of the hull is your prop shaft. If your prop shaft is real deep you are going to have to trim way up to get the boat to fly. If your prop shaft is more than 2 inches below the hull and you still want to change the drive I would try a -2 shorty if you can get your hands on one.

I'm not sure the boat will do 80 being a single 30 with HP500. 24 pitch is easier than changing drive

Dang . If your holeshot is good on a 30 cat with a 1.36 ,26 prop and what should be a combo that has more of a top end powerband flavor my vote goes to the fuel pressure gauge .or your tach is way off

My prop shaft if level with the bottom of the sponsons, I do have a -1 imco that will go on it shortly it's a 1.50 ratio, it's had a 750hp blower engine before but not sure what he was running for a prop

I have two 1.50 drives available to swap no problem and not many props that's why I was going to swap a drive

Checked the tack to a timing light and it's within a 100rpm of each other

Hows fuel ? Secondaries opening on the new motor (if carb) sounds like your familiar with boat and wouid know if its a dog out of the hole ,pulling highway gears . If your leaning out its not good for the motor long term

The secondary's are opening, and it get up on plane quick until 3k then falls on its face, fuel is good I put in 100 in each side of 91 non ethanol

We did pump accelerator pump by hand and it did pick up some so I am told the carb is an 850 but I have doubts of that I'm thinking it may have too small of a carb but not sure till I try another

Even with a 750 it shouldnt throw in the towell at 3k sure both bowls have gas in em ?
Better be hanging on when when you throw some enrichment on this at 55mph the speed jumpnmight tangle you in the drive belts or have ya grabbing a handful of distributor cap at wot.
think your onto something though . If you can still see the float levels your on easy street. Hope the engine hatch has been pulled for your convenience ..

We pulled the hatch off and my buddy pumped the accelerator pump and it picked up so I think the carb has something to do with the problem and I do think the prop and drive is a little too tall for the setup in the boat, just need some re assurance and I hope I'm on the right path lol

What is total timing set at though???

I believe he said it was 32*

If your standing on the throttle as its trying to get past 3500rpm you shouldnt be able to pump anything . Might be time for a known good carb swap , you can take a peek at the throttle plate stampings while old one is off.
sounds like someone may of slapped something together to get you in thier old boat
this is a holley double pumper with a r list number true?

Any chance the fuel pump or filter is causing the problem.

Nor short term.

Many people that sell a boat with a different motor than what they had in it, don't tune it.

Furthermore, how many boats get sold that the owner takes off their fvorite prop and throws ome other on it? A ton.

Even if running good, which it isn't, I'd be verifying carb list # and pulling it apart to see what jetting and etc is in it.

Obviously, checking timing and all other ignition parts too.

Trusting someone or assuming someone left you something correct, is a quick way down misery lane.

[QUOTE=tdpb2008;4326494]I have a 30' cobra terminator cat I had just bought it has a hp500 500-540hp it has a bravo 1 1.36 ratio and a 26p bravo prop, at WOT I'm getting between 3500-3800 rpm max @ 55-58mph I'm not sure if I have a timing issue fuel issue or if it needs a 1.50 ratio drive it planes out strong then falls on it's face at 3k rpm

Looking for some help

I don't think the 1.50 will fix your engine but I would bet it will be a better all around gear for that application.

I'm going to try a known good carb and later on I am probably going to switch to my imco 1.50 drive

IF it was running lean enough to cause the problems he is having he would get a lean POP at full throttle. IF the secondary float bowl didn't have enough fuel - same results. Either the carb is way too small or something is limiting the RPM. The fact that it comes up on plane and then falls flat tells me it is probably ignition related. If it was related to prop or gear ratio of the drive it would be a dog getting on plane or wouldn't even get on plane. It takes a lot of torque to get on plane. Either there is a rev limiter kicking in or something is holding it back.