anyone know the flow rate of the Raw Water Pump on a '93 King Cobra pump

[jmz]

Hi All,

I am converting my Donzi 22 classic boat (new engine 502 with estimated 420HP) to closed cooling with the system below.


The instruction state the below with regards to raw water pressure:

300-500HP �� capable of flowing 28 GPM @ 5000 RPM
Heat Exchanger inlet pressure (raw water) = 20 psi Minimum @ 3000 RPM
500-1200HP �� capable of flowing 35 GPM @ 5000 RPM
Heat Exchanger inlet pressure (raw water) = 25 psi Minimum @ 30

I have two full rebuild kits for the raw water pump but have still considered changing to a crank mounted pump and perhaps a combination oil cooler/ p.s. cooler. ...partly because the OMC stuff from the transom plate through the coolers is all set up for 1" hose. The heat exchanger raw water inlet is 1 1/4" so I'll either have to step up to it or change everything to 1 1/4" Honestly, I'd like to run what I've got and save the money but again I'm unsure of how much water the original KC impeller/raw water pump flows and I can't seem to find the info in my manuals or anywhere else.

Anyone out here have this escoteric knowledge I'm looking for?

Thanks

Jay

 

[HT32BSX115]

Re: anyone know the flow rate of the Raw Water Pump on a '93 King Cobra pump

Hi All,

I am converting my Donzi 22 classic boat (new engine 502 with estimated 420HP) to closed cooling with the system below.



300-500HP ? capable of flowing 28 GPM @ 5000 RPM
Heat Exchanger inlet pressure (raw water) = 20 psi Minimum @ 3000 RPM
500-1200HP ? capable of flowing 35 GPM @ 5000 RPM
Heat Exchanger inlet pressure (raw water) = 25 psi Minimum @ 30

I have two full rebuild kits for the raw water pump but have still considered changing to a crank mounted pump and perhaps a combination oil cooler/ p.s. cooler. ...partly because the OMC stuff from the transom plate through the coolers is all set up for 1" hose. The heat exchanger raw water inlet is 1 1/4" so I'll either have to step up to it or change everything to 1 1/4" Honestly, I'd like to run what I've got and save the money but again I'm unsure of how much water the original KC impeller/raw water pump flows and I can't seem to find the info in my manuals or anywhere else.

Anyone out here have this escoteric knowledge I'm looking for?

Thanks

Jay

Howdy Jay, Welcome aboard!


Well, if it's not in an OMC service manual, I don't think you'll find much (or any) info on flow rates for any of the Cobra pumps.

They are more than adequate though considering the approximate size of the impellers. Flow rates will also be dependant on the discharge hose size as you noted. Theonly pumps I have heard having problems with closed systems are Mercruiser Alpha (drive-installed) pumps not having enough flow capability. This is a FULL system or just Block/heads?

All that said, I would still switch to the engine mounted (Volvo type) pump because the KC pump kits are basically no longer available....and to improve flow you could also add a thru-hull sea-water pickup.

Sell your pump kits to some other poor soul with an Interim BB Cone-Clutch King Kobra. You won't have any problem finding buyers.

I would also install separate oil and PS coolers in the raw water line too. If you're going to run in salt, you might consider a sea-strainer.


Cheers,


Rick

Let me also add, if you REALLY want to know the flow rate, get yourself a 5 gallon pail and a stop-watch.....but the only way you'll know if it's gonna work is to just hook it all up and try it. .... more than likely, it'll work just fine. ...... If the flow is not enough, you'll notice the temp slowly creeping UP during full throttle continuous running. If that happens, back off on the throttle.

 

[jmz]

Re: anyone know the flow rate of the Raw Water Pump on a '93 King Cobra pump

- Rick.


The system is just block and heads (half system). I think you are right about everything you said. My main concern really is the 1" hose coming from the transom and coolers and then feeding the heat exchanger. The impeller in these KC drives are pretty big.

One thing I'm not real clear on is if I change to a crank mounted pump should I use a transom type pick up or simply pick up from the drive unit. I know of another Donzi 22 running an HP500 EFi using the KC drive and a merc. sea pump and they plumbed off the drive unit. I guess one just pulls out the impeller and lets the shaft turn freely. I suspect a transom mount thru hull would flow better though.

Thanks again,

Jay

 

[HT32BSX115]

Re: anyone know the flow rate of the Raw Water Pump on a '93 King Cobra pump

Jay,

I think it has been tried both ways but you remove several possible places for a leak if you use a transom mounted or through-hull raw water pickup.

Any leak between the drive and the pump would suck air and you would either lose prime altogether or have aerated water in the heat exchanger which could cause over heats.

With the poor impeller availability you may have with the cone-clutch KC pump, I would probably lean towards an engine driven pump and either a transom or thru-hull pickup if I were doing it.

 

[Scott Danforth]

Re: anyone know the flow rate of the Raw Water Pump on a '93 King Cobra pump

I would guess about 15-20GPM for an in-leg pump with a max pressure output under 20PSI - make sure you add up the entire system restrictions. the block mounted pumps are about 25-35gpm depending on the pump impeller curve and the RPM its driven at, and deliver about 25psi. These are generalities based on past experience, and by no means constitute a proper pump curve for a specific pump.

 

[jerryjerry05]

Re: anyone know the flow rate of the Raw Water Pump on a '93 King Cobra pump

The original pump setup on your KC is way more than your gonna need.
Changing to a crank drive pump is a good option.Just remember to get rid of the old impeller.
I think the KC pump is bigger than the crank mounted one.

 

[bruceb58]

Re: anyone know the flow rate of the Raw Water Pump on a '93 King Cobra pump

Eventually, you are going to have to ditch the original water pump assembly once there are no more impellers to be bought. You can either switch now to a crank mounted water pump or do it later. I would be going to a thru hull water pick up with the front engine water pump.