Water flow difference - Close-cooled 600's?
 

Hypothetically, if you had a pair of 600 hp normally-aspirated 540's with closed-cooling, and, at 5200 rpm, the raw water flow in one was 31.4 gallons per minute while the other one was 37.7 gallons per minute, and the manufacturer told you that this 20% variation between "identical" engines was fine, what would your reaction be? (This, of course, considering the fact that the first engine had melted five exhaust manifolds...)

Damn, you have been thru 5 manifolds on the one engine, and not a problem on the other. I hope this isnt common on these. I purchased new to avoid the headaches.

I still havent gotten my mill in, cant make up my mind on what I am doing.

Hypothetically, if it has melted 5 manifolds and nothing is done to fix the problem, it's just going to melt another 5 manifolds. It must have either a bad pump. a restriction some where, or a hose routed wrong. But if it's left alone you have worse problems around the corner ( like blownup motor ). What does the temp on this motor look like compared to the other?

Hypothetically, I only melted one manifold on the other engine. (Same side of the engine, though...) Let's say that there is a significant difference in the plumbing arrangements to the manifolds side-to-side, and for some reason the manufacturer did not want to change that setup.

Let's pretend that the low-flow engine had been rebuilt once (and unrelated problem), and has had a valve job due to warped valves once. Fresh water (block) temps run pretty much the same, but apparently (or obviously) the manifold temps might not....

Key question: Is 20% an acceptable tolerance, and/or is 31.7 gal.min enough?

Do you have a water pressure gauge? Maybe the engine/manifolds don't get enough water at higher speeds with the drive trimmed.

Let's say if I had water pressure gauges and they read 30 psi on one engine (31.4 gal/min) and 45 on the other (37.7 gal/min), what would you think? I would think that the 30 psi / 31.4 gal/min engine had some sort of restiction on the inlet side. Assuming the water flow numbers came off of a dyno test, it would seem that the boat/installation would not be the problem.

Mercruzer - Don't worry. These are hypothetical engines for the sake of an engineering discussion.

Remember - The questions here are:
1) Would 31.7 gal/min be enough to cool the exhausts on a 600 hp engine?
2) Would a 20% difference in water flow between the two engines worth worrying about?

Have you checked the inlets on the drives or pickups for small debris or a difference in opening size?

”Required flow in direct cooling systems is typically 10 GPM per 100 HP at maximum load and RPM for diesel engines. 11 GPM per 100 HP is the typical requirement for gasoline engines.
With closed cooling the heat exchanger should be capable of handling approximately 10% more that the maximum engine heat rejection rate and should include or be fitted separately with an expansion/header tank.
The recirculating pump should be located at the coldest part of the primary circuit and be able to maintain a water temperature differential of 45° F across the cylinder block at full load. A marine thermostat regulates the engine temperature to about 185° F (on most engines).
Required flow in heat exchanger cooling systems is approximately 15 GPM for every 100 HP at maximum load and RPM for diesel and gasoline engines. If an exhaust manifold is fitted in the raw water or fresh water circuit, the required flow should be increased by 10-15%. Any additional coolers, such as oil or charge air coolers, must be fitted after the pump and require 10-13 PSI of water at maximum engine RPM.”

1) If this applies to your application you are @ < 6 GPM per 100 HP
2) Both engines would be well below spec, one marginal and one at failure.
3) It would seem that low pressure/low volume would be an inlet side restriction and high press/ low volume would be a downstream restriction
I can verify this information as per your particular setup
Bob

RMBuilder (Bob) - Now THAT'S the kind of answer I'm talking about! :) Now, let's say the flow was arranged in this fashion:

Drive/transom -> sea strainer -> raw water pump -> fuel cooler -> oil cooler (water pressure reading taken at inlet side) -> power steering cooler -> engine heat exchanger -> exhaust manifolds (via 2 separate outlets from the H/E).

I'm assuming that the pressure reading would rise as the square of the flow rate, so that an increase of 20% in flow (from 31.4 to 37.7 gal/min) would yield an increase of 44% in pressure (from 30 psi to 44 psi), which is almost exactly the gauge numbers I quoted. Am I right?

zahndock - The hypothetical water flow numbers in gallons per hour would be from a dyno, thereby eliminating the boat as a source of restriction.

Chuck, have you ever taken a pressure reading at the strainers running? Is it a step bottom? For what its worth, I ran 620 hp/502's (naturals) with alum heads and the relatively inexpensive closed system out of Long Island with std merc pumps, same exhaust as you, thru Mayfair strainers, pickups at bottom of transom, 1 1/4" marine hose from transom to strainer to Merc seawater pump, no thermostats and never had any heat problems. I thought this was taken care of? Are you back at Tomes this year?

Bob: I'm fine. This is a theoretical discussion for a friend. We're still at Tomes.

Flow readings would be from the dyno, indicating that the boat's not the issue. Strainers would be Gils.

Flow numbers aside, my gut reaction is that:

* if the block temps (at the thermostat, assuming that water flow is in the normal "in at the circ pump and out at the stat housing" direction) are within spec (less than 190)...

* and you are introducing exit water from the H/E to the BOTTOM of the manifolds...

then you should not be damaging manifolds unless one side is getting all the flow, leaving the other side dry.

I'm all into specs and math, but you are telling us that the setup (both setups actually) is containing block temps well and is not showing heat saturation. The exit water from the H/E is not going to be any warmer than the exit coolant from the block. Can't be. Defies physical laws.

If you're feeding manifolds with 190 degree water at half of 30gpm (which it won't be that hot cause it cannot exceed or even match the block coolant temp) then even if it boils in the exhaust mans, the heat energy required to trigger the phase change will be removed from the manifold and should keep it "safe". Where there is a problem, though, is that I don't honestly think you CAN flow 15 GPM from the bottom of most manifolds. I don't think it will flow that much volume. You can dump a pretty healthy chunk into the tailpipes, but I don't think you can get that much thru the bottom of a manifold. Enough pressure, though, and you can do about anything. 30psi is a pretty good amount of pressure.

NOW, I've seen applications that integrate the bottom half of the manifolds into the closed (antifreeze) loop which dumps the heat back into the H/E. This requires more of the H/E, but ensures that you CAN't have a heat failure of the manifold without seeing it coming from a long way out via the temp gauge.

Keep us posted. This is interesting.

That's one part of the equation that makes a whole lot of sense. Say the right side has a sharp (forged) 1" hose barb x 3/4"NPT 90 degree fitting leading into it while the left manifold has a straight fitting (same sizes). As the water flow rate goes up, the effective restriction of the 90 degree fitting would just get worse and worse, wouldn't it? In other words, at idle (say 15 gallons/minute), the flow rate out of the two tailpipes might not be much different, but at higher rpm, the right manifold might not see nearly as much water flow, would it?

Chuck,
The resistance @ the 90* would increase as both flow and pressure increased not to mention the interference due to the return pressure pulse of the coolant striking the outside radius at that angle.
The pressure/velocity differences in the inner/outer radii could aerate the coolant thereby reducing its thermal conductivity from that point.
Bob

Ok - That pretty much explains my theoretical issues. RMBuilder - What was your source for the quotes in post #8.

Thanks!