Crossover vs Water Pump
11-28-2003, 08:04 PM
#1
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Posts: n/a
Crossover vs Water Pump
I recently read that Hardin Marine has come up with a crossover with an idler pulley mounted to it so that 454/502 Mercs with serpentine belts can eliminate the water circ pump for a CLAIMED increase of 15 - 20 hp. What does everybody think? Does the pump eat up that much power? Are there any disadvantages to swapping for a crossover?
11-29-2003, 07:11 AM
#2
Registered
Pro's....Maybe 5-10 hp.....You wont notice
Con's...Some people run into water pressure problems, Have to run dumps
Chance of steam pockets in back of heads
$$$...That could be spent on other inprovements
Con's...Some people run into water pressure problems, Have to run dumps
Chance of steam pockets in back of heads
$$$...That could be spent on other inprovements
11-29-2003, 08:45 AM
#3
VIP Member
VIP Member
birdog is right... waste of money...
I have spoken to a number of marine mechanics about the subject. Not one has suggested that eliminating the circ pump is a good idea...
I have spoken to a number of marine mechanics about the subject. Not one has suggested that eliminating the circ pump is a good idea...
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Patrick
Patrick
11-29-2003, 09:13 AM
#4
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hey birddog what causes the steam pockets in the back of heads i read somewhere that people are taping the rear of there heads and install a fitting to dump the water out the transom to relieve that problem. what have you heard
11-29-2003, 10:01 AM
#5
Charter Member
I tapped and installed steam lines on my last motor. Just tapped into rear of intake and connected to front water jackets. Don't know if it worked as I don't know if I had a problem before hand. Once of preventention.....
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Last edited by US1 Fountain; 12-02-2011 at 11:17 AM.
11-29-2003, 01:00 PM
#6
Registered
Good topic Ric232; it needs a good thrashing.
When the crossover kits first came on the market we were told that they allowed more water flow to the heads. This was supposed to be a good idea on supercharged engines. I think it may have had more to do with getting clearance for blowers and blower drives. Some people like the look.
The recirc pump is only necessary when operating in cold climates, because the T-stat may stay closed for a while. But not much volume of water is involved (think about the small size of the recirc hose under the T-stat that feeds the pump). Once the T-stat opens there is little or no recirculation. So if you don't operate in cold climates, you don't need it, and nothing bad is going to happen if you remove it. I don't know how much power it consumes. Did Hardin do a dyno test to get their number?
That leaves two other questions:
1) Does the crossover kit really increase water flow?
2) Does the crossover kit affect water distribution?
Distribution:
Water goes into the block through the two holes on either side of the timing cover and makes its way to the back of the block bleeding into the heads through various holes which make up parallel paths back to the T-stat. Since there is a lot of water in the block it acts as a reservoir or plenum which, when pressurized, should deliver flow to each water passage in the cylinder head equally. There is a limit to this pressure before water starts leaking past gaskets into cylinders and lifter valley.
That's the easy part. Now the water in the jackets around each combustion chamber has to get back to the front of the engine. Without a big plenum to balance this flow out, you would have to purposely make the front passages more restrictive than the back ones so that water flow would distribute itself equally across all cylinders. I can only assume that when GM designed this system they made sure the flowrate from the back of the cylinder head was the same as the front. Is it designed right? Is this something we should be messing with? Don't know.
So if we're talking about the distribution of water flow in the block and to the cylinder heads, I don't think it matters whether their is a recirc pump or crossover in front of the block. Once the water enters the block and the T-stat is open, distribution of water is set. If you're having a problem with the back cylinders then maybe GM didn't design well and flow is short-circuiting through the front water passages. Or the back cylinders are hot for another reason, maybe fuel distribution?
Flow:
The stock configuration has three water pumps in series; two belt driven plus the pumping effect of the water pickup at speed. The stock configuration also has pressure relief valves built in. If you add a crossover and remove Mercury's big T-stat/pressure relief block, you must also install a pressure relief valve. There are numerous threads on OSO on this subject.
Since the crossover eliminates one of the pumps, how could it increase flow? Because under certain conditions the recirc pump could actually be a restriction to flow. When the system curve (the combined resistance of the whole water pathway) does not intersect the combined curve of the pumps in series, the sea water pump and water pickup "pump" can flow more water with the recirc pump removed. All the recirc pump could maybe do is add more pressure, which you don't need anyway.
I'm just repeating this out of a book, I don't understand it either.
I just think of the sea water/pickup pump as the "Big" pump that can do a better job if the "little" pump would get the hell out of the way.
Do you need this extra flow? I don't know. If your block pressure is already at the limit with the stock setup, you can't flow anymore water into the cylinder head passages without increasing block pressure and risking leaks.
Is there another way? Can you increase flow through the heads by reducing resistance on the downstream side? Yes! I like the idea of allowing water to get out of the back of the heads, because I wonder if GM's design is good enough for 700 HP boat engines. Maybe the back cylinders do need help. But I wouldn't plumb that water back to the T-stat, I would run it overboard. However, I'm a little concerned about upsetting the distribution if GM has got it right.
Conclusion:
Block pressure limits the amount of flow into the heads. If the crossover increases block pressure over the stock configuration, it will increase flow, but pressure relief is still required.
Releasing water at the back intake manifold passage may increase flow through the back cylinders. The size of the fittings must be carefully chosen to avoid starving the front cylinders.
P.S. Nice looking blower setup US1 Fountain. What's it on?
When the crossover kits first came on the market we were told that they allowed more water flow to the heads. This was supposed to be a good idea on supercharged engines. I think it may have had more to do with getting clearance for blowers and blower drives. Some people like the look.
The recirc pump is only necessary when operating in cold climates, because the T-stat may stay closed for a while. But not much volume of water is involved (think about the small size of the recirc hose under the T-stat that feeds the pump). Once the T-stat opens there is little or no recirculation. So if you don't operate in cold climates, you don't need it, and nothing bad is going to happen if you remove it. I don't know how much power it consumes. Did Hardin do a dyno test to get their number?
That leaves two other questions:
1) Does the crossover kit really increase water flow?
2) Does the crossover kit affect water distribution?
Distribution:
Water goes into the block through the two holes on either side of the timing cover and makes its way to the back of the block bleeding into the heads through various holes which make up parallel paths back to the T-stat. Since there is a lot of water in the block it acts as a reservoir or plenum which, when pressurized, should deliver flow to each water passage in the cylinder head equally. There is a limit to this pressure before water starts leaking past gaskets into cylinders and lifter valley.
That's the easy part. Now the water in the jackets around each combustion chamber has to get back to the front of the engine. Without a big plenum to balance this flow out, you would have to purposely make the front passages more restrictive than the back ones so that water flow would distribute itself equally across all cylinders. I can only assume that when GM designed this system they made sure the flowrate from the back of the cylinder head was the same as the front. Is it designed right? Is this something we should be messing with? Don't know.
So if we're talking about the distribution of water flow in the block and to the cylinder heads, I don't think it matters whether their is a recirc pump or crossover in front of the block. Once the water enters the block and the T-stat is open, distribution of water is set. If you're having a problem with the back cylinders then maybe GM didn't design well and flow is short-circuiting through the front water passages. Or the back cylinders are hot for another reason, maybe fuel distribution?
Flow:
The stock configuration has three water pumps in series; two belt driven plus the pumping effect of the water pickup at speed. The stock configuration also has pressure relief valves built in. If you add a crossover and remove Mercury's big T-stat/pressure relief block, you must also install a pressure relief valve. There are numerous threads on OSO on this subject.
Since the crossover eliminates one of the pumps, how could it increase flow? Because under certain conditions the recirc pump could actually be a restriction to flow. When the system curve (the combined resistance of the whole water pathway) does not intersect the combined curve of the pumps in series, the sea water pump and water pickup "pump" can flow more water with the recirc pump removed. All the recirc pump could maybe do is add more pressure, which you don't need anyway.
I'm just repeating this out of a book, I don't understand it either.
I just think of the sea water/pickup pump as the "Big" pump that can do a better job if the "little" pump would get the hell out of the way.Do you need this extra flow? I don't know. If your block pressure is already at the limit with the stock setup, you can't flow anymore water into the cylinder head passages without increasing block pressure and risking leaks.
Is there another way? Can you increase flow through the heads by reducing resistance on the downstream side? Yes! I like the idea of allowing water to get out of the back of the heads, because I wonder if GM's design is good enough for 700 HP boat engines. Maybe the back cylinders do need help. But I wouldn't plumb that water back to the T-stat, I would run it overboard. However, I'm a little concerned about upsetting the distribution if GM has got it right.
Conclusion:
Block pressure limits the amount of flow into the heads. If the crossover increases block pressure over the stock configuration, it will increase flow, but pressure relief is still required.
Releasing water at the back intake manifold passage may increase flow through the back cylinders. The size of the fittings must be carefully chosen to avoid starving the front cylinders.
P.S. Nice looking blower setup US1 Fountain. What's it on?
Last edited by tomcat; 11-29-2003 at 01:08 PM.
11-29-2003, 02:15 PM
#7
A friend of my owens a dyno shop called Dyno Tech in Memphis and his 572 14/71 blower motors that made 1122hp. No innercooler,On this motor they added the pluming from the rear to the front it picked up 15 hp . these were the big chief style heads . They figured it had some hot spots in the back of the heads.
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The Only Time You Have To Much Ammo Is When Your Swimming Or On Fire.
11-29-2003, 02:54 PM
#8
tomcat, thanks. It was on an HP465. I have since sold it to member Baddog. I don't know if he has retained the steam lines or not. Tim?????????
As far as equal block water circulation with a crossover, I know of one member that has a Troy Dennis blower motor and his front water passages are blocked off. Instead, he uses the center freeze plug holes on both sides as the inlets.
Theory is that cold water always enters at front 2 cylinders under normal stock setup, and will make for uneven cylinder temps. Front cold> center warm> rear hot. (exaggerated) The center inlet setup gives a more balanced effect.
You need enough water pressure to keep the block and heads filled, and enough flow to keep cool. But too much or too little of either is undesirable, let alone time bomb. Alot of people will play with the pressure relief and flow control aspect and get the gauge reading just fine, and 99% this will be fine. Be interesting to take a infra ray temp gun on each cylinder and read the difference individually, vs as an average, which is what the dash gauges are showing. Water pressure should be pretty consistant thru out within a couple #'s.
This stuff is to indepth. Makes my head hurt.
Some times too many gauges causes more worry than needed.
As far as equal block water circulation with a crossover, I know of one member that has a Troy Dennis blower motor and his front water passages are blocked off. Instead, he uses the center freeze plug holes on both sides as the inlets.
Theory is that cold water always enters at front 2 cylinders under normal stock setup, and will make for uneven cylinder temps. Front cold> center warm> rear hot. (exaggerated) The center inlet setup gives a more balanced effect.
You need enough water pressure to keep the block and heads filled, and enough flow to keep cool. But too much or too little of either is undesirable, let alone time bomb. Alot of people will play with the pressure relief and flow control aspect and get the gauge reading just fine, and 99% this will be fine. Be interesting to take a infra ray temp gun on each cylinder and read the difference individually, vs as an average, which is what the dash gauges are showing. Water pressure should be pretty consistant thru out within a couple #'s.
This stuff is to indepth. Makes my head hurt.
Some times too many gauges causes more worry than needed.
__________________
Some people are like Slinkies - Not really good for anything, but they
bring a smile to your face when pushed down the stairs.
Some people are like Slinkies - Not really good for anything, but they
bring a smile to your face when pushed down the stairs.
11-29-2003, 02:57 PM
#9
Registered
$.02
A circ pump has no suction, so it does not help you if a raw water pump goes bad. However, if a circ pump goes bad, your raw water pump cannot pump past it,so again it does you no good.. Get rid of it..
Scott B
A circ pump has no suction, so it does not help you if a raw water pump goes bad. However, if a circ pump goes bad, your raw water pump cannot pump past it,so again it does you no good.. Get rid of it..
Scott B
11-29-2003, 03:03 PM
#10
Originally posted by Scott B
$.02
However, if a circ pump goes bad, your raw water pump cannot pump past it,so again it does you no good..
Scott B
$.02
However, if a circ pump goes bad, your raw water pump cannot pump past it,so again it does you no good..
Scott B
The impellor in the circ pump is not 'sealed' like in your raw water pump.
