King Cobra

[springs]

I posted earlier this summer about the 22 classic I had bought w/460 twin turbos-King Cobra. Since that post I have had many many problems all stemming from the turbo set-up and the lack of knowledge on my part. I won't get into great detail but the turbos had no wastegates and I could never get the fuel to air ratio right. Well to make a long story short I burnt three pistons. I finally came the point where the turbos had to go. After $2000 for a set of cast iron Cobra Jet heads(used but really worked), new cam, lifters, pushrods, pistons, and Dominator carb I'm about a week away from going back in with the 460 (now 477) straight horspower motor. I don't think I'll spend the time and money to have it dynoed but I feel pretty confindent that I've broke to 500 horse mark. Now I guess I'll get to the point. I have done numerous searches on the registry trying to find discussions of prop selection for King Cobras in high horsepower set-ups and haven't had much luck. I'm not really in a locale to have an abundance of test props to try since light tunnel boats w/ 300HP outboards seems to be the rave around these parts (I may never be as fast but I sound so much better). So without further ado is anyone on the board kickin' 500horse w/ King Cobra.

[Ranman]

Springs,

Before you install this "new" motor and move forward, you may want to post the specs of the components you are running. Is this motor a true marine motor or is it essentially a built car engine? Do you know the cam specs, compression ratio, valve size and type? What exhaust setup are you planning to run? 500HP is not out of the question for a BB, but it certainly has to have the right components to work properly. It's much easier to build a 500HP car motor than it is to build a 500HP marine motor.

The point I'm trying to make is that I've learned that you really need to have the motor built for the marine environment. For example if you run a radical cam, you stand the chance of experiencing reversion. This is when the exhaust valve is still open when the piston is on the down stroke causing the engine to suck water in from the exhaust. This is detrimental to the engine and occurs frequestly with big cams. There are some basic limitations of the cams you can use without causing reversion. If you do go with a bigger cam, you need the water to enter the exhause stream further down the line. Other experts here can tell you what you can and cannot get away with.

Lastly, once you are sure your motor is suitable for marine use, spend the cheese and have it dyno tuned. This will give you and exact HP output figure, allow you to optimally tune the motor and will ensure that what you have done is correct. In my honest opinion, if you don't do this, it will most likely cost you more in the long run because you will have that motor in and out of your boat over and over constantly chasing problems. Do it right the first time and enjoy your boat. Good luck with your project.

[RickSE]

What prop do you have now? I'd run it with the prop you have to get a baseline then figure out what you need from there.

[BUIZILLA]

Hi, in my opinion, I would NOT use the Dominator carb, unless it was the 750cfm edition. If it's a 9375-1050 or 9377-1150, it'll run like crap. No, actually, it will run worse than that... I know my way inside and out on Dominators like no tomorrow, I have several on the shelf, including 2 for alchohol wink ..

You'll be MUCH happier with a NEW HP series 850 vacuum or 930 vacuum secondary model, with the adjustable secondary pod, for tip-in acceleration, and 4 corner idle control. I just happen to have a HP930 sitting here.. great carbs, usually right outa da box.

You didn't say what intake manifold your using though... does it have *both* carb base bolt patterns?? single or dual plane??

J

[springs]

Ranman
This is the same marine 460 that came out of the boat. Just different heads and cam. Same forged crank and connecting rods. Valves are 2.25 intake 1.88 exhaust. 1.625 240lb Valve Springs Comp Cams 280 duration .530/.530(mean but not nasty). JE flat tops. Jesel belt drive and Mallory unilte dist. Also added hi-performance oil pump and windage tray.
This motor should run strong and be reliable.

Buizilla
I'm still looking for a Victor Intake but for the time being I'll be using a cast iron Super Cobra Jet using a 4150 to dominator adapter plate. As far as the carb its a 1050 Dominator. We just bought a King Demon for the grudge car so I was planning jetting down the Dominator and using it.

[BUIZILLA]

What's the list number of the carb you intend to use?? If it's a 9375... fergit it. If it's an 8896, you may be okay... I still think it's WAY toooo big a carb for your application, unless of course your turning it WAYYY past 6000 rpm :D

J

[springs]

It probably is a bit to big. An 850 would probably do a good job. I'm gonna see how it works with what I already have before I spend any more money. I've still got the 790 that came on the motor but I'll need to get a new base plate for it.

[springs]

Sorry Rick. Missed your post. I have a 21 pitch omc prop that came with the boat that is in terrible shape and they day I burnt the pistons I was trying out a 21 Laser off my formula. Not really tring it out but knew It would have to work better than the OMC.

[RedDog]

For what its worth, I am running around 400 HP through a King Cobra mounted on an 18 Classic. I am using a 22" OMC Raker and on the days I can stay in the throttle it will spin it a little over 5000.

[Greg K]

You didn't mention what head gaskets you're using either and the type of valves you installed in those heads. What type of exhaust will you have too?
As for a basleine on the prop, if you really feel you have or going to end up with 500 HP, you'll need at least a 26" prop.
I recently dropped a new 502 (my setup estimate 450 hp) into my 22, King Cobra drive and have been playing with a 25" Turbo 1 prop. So far I've turned my motor 4800 max so far only for a few seconds. FWIW

[springs]

Greg
Gaskets are FelPro marine and stainles ferrea valves. What kinds of speeds are you gitting at 4800 RPM.