Maxum 2400scr prop size cooling system?

[Hmaninvan]

Hello All,

1. whats the best size prop for top speed? i'm doing 29 now at 4000rpm

2. has anyone been successful in a full loop cooling system? i just replaced the manifolds, wondering if i can modify to loop in the cooling system? salt water is killing me!!

ty,

Harris

[mmwjr]

First what engine and drive do you have, also what is the prop size you are currently running with?

Do you currently have closed cooling on the engine? Half system, engine only?

If so the HE is not sized to switch to full closed cooling.

If the system is open you can buy a full closed cooling system to protect the engine and manifolds.

[Calguy]

Depends on drive. Is it Alpha or Bravo ? Bravo drives allow for much larger props. I have a 2400 SCR running a B 2 and getting 38 mph at 4K RPM.

I would be careful changing to a closed cooling system after years of salt water use. Pressures within the closed system are higher and could cause problems with head gaskets, etc. I suggest a Perko Flush Pro if it is a Bravo drive as the engine can be flushed even while the boat is in the water.

[Hmaninvan]

Thanks,will get prop size and leg

[shrew]

It's like you hijacked your own thread with two unrelated topics. Now, I don't care, but replies are going to start splitting focus between the two topics.

As for Propping, First, I would take the boat out on some relatively calm water. Get the boat up on plane and the drive trimmed out properly (Preferably with as little tab as possible). Then get to the Wide Open Throttle (WOT).

Now determine whether the Max RPM's are within the Max RPM range for the engine.

If you are below the Max range, then you are overpropped and probably want to go down in Pitch. If you are over the Max range, then you may want to increase pitch.

3 blade vs. 4 blade and SS vs. Aluminum will also have some impact.

It would help to get the following info.

Engine displacement
engine HP
Carb or fuel injected
Drive type
drive gearing
boat length, beam, draft, weight

[mdtraveler11]

Good topic, I will be following this one. Both the Prop info and cooling. I'd like to know how many people rinse with fresh after running salt each time.

[mmwjr]

Originally Posted by mdtraveler11

Good topic, I will be following this one. Both the Prop info and cooling. I'd like to know how many people rinse with fresh after running salt each time.

When you say rinse with fresh water are you referring to flushing the engine or wash the boat off?

[mdtraveler11]

Flushing the engine with fresh water after running in salt. Do people generally try to do it every time or just periodically or just seasonal.

[mmwjr]

Generally you will find all. I think a driver come down to is the boat kept in the water or not. Even if kept in the water there are flushing kits but with drives that have the impeller in them it makes it more difficult. Lift or trailer kept is must easier.

If I were to do so I would use a product like salt away as just flushing will leave salt behind.

With that said I have had 3 boats and have used them nearly weekly so I only flush when I winterize.

[Hmaninvan]

I have some info. Prop size, 3 blade stainless 14x25 RH

[Hmaninvan]

Originally Posted by Hmaninvan

I have some info. Prop size, 3 blade stainless 14x25 RH

5.7 merc alpha 1leg second generation.

[mmwjr]

That's a lot of pitch in that prop.

Mercruiser has a prop calculator on their WEB page that I recommend trying.

I would think something more like 13.5 x 19

[Hmaninvan]

Got some info. Took the boat out last night. Wide open at 4000 rpm no more left 29 miles an hour.

5.7 Alpha 1 2nd generation. I posted prop pitch eairler.

Am I over propped?

[mmwjr]

Originally Posted by Hmaninvan

Got some info. Took the boat out last night. Wide open at 4000 rpm no more left 29 miles an hour.

5.7 Alpha 1 2nd generation. I posted prop pitch eairler.

Am I over propped?

A WOT of 4000 is overproped as the WOT should be 4600 - 4800. Dropping pitch by one size will gain about 200 rpm.

Either a 21 or 19 inch pitch sounds a better choice.

[shrew]

I agree. Technically the max rpm range is 4400-4800, however I agree with mmwjr, the target for 'prop tuning' should be more like 4600-4800. The closer you are to the max of 4800 the better. You definitely DO NOT want to be out of the range on either end.

[shrew]

Mercruiser Prop Selector:

https://www.mercurymarine.com/en/us/...tor/#/step-one

You should be somewhere in the 18-20 (19-20) pitch range. Run through the propr calculator and see what you come up with.