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View Full Version : Crossover theory, continued...



cutwater
07-02-2008, 03:08 PM
I have collected some good posts regarding crossovers from a thread I have bookmarked. This should help for future reference since the search feature is broken and only works for 2008 posts and posts from 2004 and prior. I found most of these things to be true in my recent adventure with installing the SM crossover - especially the part about expecting uneven water flow and having the bottom riser water dumps closed off when using the drive impeller. Just thought I'd share.

Joe - on running a crossover using only the Alpha's impeller...

Personally, I don't think an Alpha will pump enough water. I know that Budman had a sea water pump installed on the engine he just had made. Seems to me that every Alpha has steam coming from one side, which I would attribute to lack of cooling water, but I could be wrong. Gcarter has a crank mounted sea water pump, but I don't remember if he kept the circ pump or went with a cross over.


BigGrizz - on water pressure regulation - it's why I use a relief valve...

As for crossover causing problems is not BS. Anything over 35psi in the block is detrimental to head gaskets. It just happens to be more prone to the problem then circ systems, circ systems have it too just not so much due to application Race boats have relief valves for this reason. think about this the first place the cold water hits is the front of both heads than block then t-stat. if the state is open, takes a while to close, then the exhaust. Garry Grimes designed the one tat Mercury sells. If you look at some engines and you see rust from the head down the block this was probably the cause. This is especially true on blower and high compression engines. with a circ the impeller restricts the flow of warer. Now in most applications that the average 65-70 mph unit it is on the verge, especially with hull pickups and re entry. My Criterion would surge upto 32 psi at 78 untill i put on the closed system. I won't go into the temperature differential thing because have done this on the net before. Believe me it does exist.


Brownie - multiple:

The alpha pumps enough for a small block, probably not for a big block. If you have that combo, you may need to weld up some of the bottom holes on the riser dumps to force the cooling water to the top when idling (to keep your skin from sticking to it)

No matter what you do when you remove the circ pump, you must introduce the water into the same two holes that the circ. pump did.

If you run a thermostat on the crossover application (a must to me), you must drill 3 5/32" holes in the crown of the thermostat to allow water to bypass at all times. All thermostats are automotive based, and are expected to have the same (more or less) temperature on both sides of it. If you install a standard thermostat, the temperature will spike LIKE CRAZY.

The circ. pump belt is a fractional horsepower belt. How long do you think it would last on a 20HP Go-Kart?


BigGrizz - on why you should listen to Brownie :wink:

My suggestion is listen to Brownie. I have know him a long time and as of yet have never found him wrong. When he says I prefer, that means you should do it, when he says a must to me that means do it or pay the concquences.


Mario - GREAT POST!!! Where have you been?

Thermostats . . a few things seem to be getting missed here . .

They maintain a constant engine block temperature . . atleast they are supposed to

Holes are drilled in the top to maintain flow but most of all to bleed out air, as air pockets restrict water flow and a thermostat will not open unless it is submerged in water . .

As Brownie stated, an Alpha water pump is inadequete at idle to create enough water pressure or flow to push all the air through the bleed hole that should be in every thermostat . . and these need to be installed with the bleed hole at the top. Drilling a larger hole reduces the back pressure on the Alpha drive pump, allowing full water circualtion before the engine overheats. Restricting the risers ensures water is everywhere it needs to be.

Mercruiser 260 HP Alpha set ups come with a circulation pump . . for a reason. Service is easier with stock off the shelf components versus modified t-stats and welded risers . . .plus the pumps help to balance the flow to both sides of the V8. Cross over tubes, especially those where the inlet comes from one side, will not have a balanced flow.

In a marine application with fresh water cooling . .or sea water cooling a thermostat is still essential . . you do not want to inject 55 degree water into an engine at one end while it exits at 160- 180 some where else . .

Know that the block temperature at the inlet will barely rise above the inlet water temp, while the temp at the exit, or close to that will exceed 160, especially at the heads on top of the combustion chambers. This is not a good thermal equilibrium for the engine . . and can lead to headgasket failure . .especially with aluminum heads . . .


Gcarter, on your picture you show a crank driven pump. Please watch out for the front cover. The gasket is teflon or plastic, and when run at high rpms the pump will create enough pressure to push the gasket out. It is only clamped between two flat surfaces. I have the same pump, BTDT 2x and am now getting a cover made with an O-ring seal.

Mario


Brownie - on cooling systems...

The mission of the cooling system in a marine engine is is to keep the block at the CORRECT temperature. The word cool does not figure into the equation. The engine in your vehicle runs 200+ degrees at high output. They could make it run cold IF THEY WANTED TO. Clearances, evaporation and other factors make the engine want to be WARM. If you think that the mission is to run as cool as possible, you are waaaay off base. Some Gorilla motors have such a heat rejection problem (related to fuel consumption) that they keep all the obstructions out of the cooling path, and the BTU from burning 100 gallons per hour of gasoline keeps the motor warm. You must have seen the ads that claim that 75% of engine wear occurs at start up. When I worked for Tom Gentry on the "Gentry Eagle", We had to warm the 3600 HP MTU Diesels for 5 hours BEFORE WE COULD START THEM. Why do you think that was?

VetteLT193
07-02-2008, 03:27 PM
I'll find out soon about the Alpha / crossover combo. :eek!:

I have to ask my brother if he ran a crossover on his original engine, I am pretty sure he did, 454 / Alpha 1, and he had over 1000 hours on it.

I do not like the Alpha flow at idle, but it is fine at 1000 RPM. I don't run dead idle very often.

cutwater
07-02-2008, 04:47 PM
I'll find out soon about the Alpha / crossover combo. :eek!:

Well, I am just using the impeller in my Cobra outdrive, but I am using risers that have the bottom dumps welded closed. It seems to work pretty well. I would recommend it.

blackhawk
07-02-2008, 04:57 PM
I've seen a few crossover posts lately? Why are so many people running them?

VetteLT193
07-02-2008, 05:02 PM
I've seen a few crossover posts lately? Why are so many people running them?

My main reason is it is one less thing to go wrong. The extra couple HP (big whoop) and reduced weight are just bonuses.

cutwater
07-02-2008, 05:06 PM
I've seen a few crossover posts lately? Why are so many people running them?

The posts are mainly me :doh:. My circ pump quit, causing my exhaust hoses to burn up... I can change an impeller in 10 minutes on my drive, but the circ pump is a hassle... A crossover means one less thing for me to worry about.

VetteLT193
07-02-2008, 05:13 PM
Well, I am just using the impeller in my Cobra outdrive, but I am using risers that have the bottom dumps welded closed. It seems to work pretty well. I would recommend it.

A package came in from DonCig a couple days ago, think they will make a difference one way or the other? The dumps are way down at the tail end of the pipes and they look threaded like I can put a small plug in them.

BTW: If you ever buy something from doncig, he'll take his time packing but it's worth it. best packing job ever.

cutwater
07-02-2008, 05:19 PM
There you go, making me jealous again... I would say you'll be fine with those - I was running the old OMC log exhaust.

blackhawk
07-02-2008, 05:36 PM
The posts are mainly me :doh:. My circ pump quit, causing my exhaust hoses to burn up... I can change an impeller in 10 minutes on my drive, but the circ pump is a hassle... A crossover means one less thing for me to worry about.

Okay that makes sense. I thought people were taking off perfectly good water pumps to gain 2 hp! :D

BigGrizzly
07-02-2008, 05:59 PM
BH funny when I built the 502 for the Criterion I added the circ pump and took the crossover out of the parts and threw it in pile of scrap. In 1970s General Motors released a graph showing the engine wear in relation to cooling water temps it went along with all the findings we found at Honda. Remember heat is horsepower. If an engine doesn't generate heat it doesn't go, unless it is a liquid nitrogen engine. I am glade you found these posts they are worth reviewing.
One thing more on the plus side of circ pumps. Once my son's impeller broke on his stock motor but the circ pump kept a small amount of water flowing and saved his engine. when we took off the raw water pump the fins were in the oil cooler. Lucky day for the kid. I mentioned this to a tech and he said he has seen it before. I never though that would happen.

gcarter
07-02-2008, 06:38 PM
When I bought the San Juan cooling system, I called them up and asked a bunch of questions.
One of the things the engineer I was speaking with told me was the stock Alpha drive mounted pump was really inadequate in warmer water (80*-95*). He told me the impellor was too short and the vanes too long. In fact, at some certain temperature, the vanes stop following the wall of the pump housing and virtually not pump. He went on to say a closed system in such circumstances would run hot.
I was already going w/the crank driven pump, but it was good to know I'd made the right decision.

VetteLT193
07-02-2008, 06:55 PM
When I bought the San Juan cooling system, I called them up and asked a bunch of questions.
One of the things the engineer I was speaking with told me was the stock Alpha drive mounted pump was really inadequate in warmer water (80*-95*). He told me the impellor was too short and the vanes too long. In fact, at some certain temperature, the vanes stop following the wall of the pump housing and virtually not pump. He went on to say a closed system in such circumstances would run hot.
I was already going w/the crank driven pump, but it was good to know I'd made the right decision.

I think I saw MOP selling a belt driven raw water pump on another forum (boat freaks?) I may go that route too. I have the new alpha in the garage so I could pull the pump now while I'm fairing in the nose cone.


There you go, making me jealous again... I would say you'll be fine with those - I was running the old OMC log exhaust.

Don't be jealous, I bought the exhaust before my trailer broke. A nice exhaust won't get your boat to the water. :hangum:

MOP
07-03-2008, 07:52 PM
Well, I am just using the impeller in my Cobra outdrive, but I am using risers that have the bottom dumps welded closed. It seems to work pretty well. I would recommend it.

The Cobra pump is larger and pushes a lot more water then the Alpha fear not, the Alpha pump is nothing more then an outboard setup.

MOP
07-03-2008, 08:10 PM
Stirring the pot!
I do not feel that adding a cross over has any effect what so ever on pressure within the system. What does effect the system pressure is the type of water pickup and speed! I feel every raw cooled engine whether or not you have $$ in it or not should have a way to relieve excess pressure to protect it. A completely stock I/O setup will run in the 30+psi at much more moderate speeds then we run. 30psi sooner or later make the head gaskets weep. System pressure should be limited 20 psi, water flow and not pressure is what is important. The exhausts ability to dump water is important, what it cannot dump must be relieved in some other way. You can check pressure any where within the system, block, manifolds etc. it will be constant throughout the system that is simple physics! As mentioned in the post clips above the Tstat needs to be modified, other then that I would say go for it!

donzi2287
07-03-2008, 09:28 PM
I think I saw MOP selling a belt driven raw water pump on another forum (boat freaks?) I may go that route too. I have the new alpha in the garage so I could pull the pump now while I'm fairing in the nose cone.
Don't be jealous, I bought the exhaust before my trailer broke. A nice exhaust won't get your boat to the water. :hangum:yes, but it sounds good

Lenny
07-06-2008, 11:04 AM
Does the crossover "kit" from Stainless Marine require the T-stat (included) to be drilled? I have a Jabsco high volume crank driven water pump (sucker).
Water dumps into SSM manifolds too.

MOP
07-06-2008, 11:19 AM
JMO It cannot hurt to at least enlarge the venting hole in the Tstat, Allan Brown recommended 3 5/32" holes, I think that is a little over kill but I feel the added flow is needed. Worst scenario it will take a few minutes longer to warm up!

BigGrizzly
07-06-2008, 05:44 PM
I believe the Stainless Marine comes with 3 5/32 already drilled.