This was done by Jerry it has a lot of very good infirmation
Why the cooling system mod is imporant
First you need to know how the cooling system in the car works.
The water pump sucks water through the radiator. This water then goes through the water pump and is pushed into the engine block in the holes behind the water pump. Once the coolant is in the engine block it then passes through the restrictions in the head gaskets and into the cylinder heads. Ultimately the coolant wants to go back to the water cross over at the front of the intake manifold (or that large tube assembly on a 4V), through the thermostat and back into the radiator to get cooled and start all over.
There are however a few other things to note. Water wants to take the path of least resistance. Meaning, water doesn’t flow up hill, it wants to take the shortest path it can to where it wants to go (it’s one of the laws of physics things). So, if the water goes into the block at the front, and ultimately wants to end up about 8” above where it entered the block at (where the water cross over is), how do you get the water to the back of the motor?
Well first off there are holes in the head gasket that restrict how much water can go through the head gasket and into the cylinder head. In most cases these restriction holes are smaller at the front of the motor and get larger as you go toward the back of the motor. In theory this makes the “path resistance” close to being equal from the front of the head to the rear of the head.
Now, on a Mustang engine, on the passenger side cylinder head (if it’s a 4V) or in the back corner of the intake (if it’s a 2V), there is a hose that goes to the heater core. This hose brings hot coolant into the heater core. The tube that runs under the intake manifold brings the coolant out of the heater core and back to the water pump. From the water pump this coolant gets circulated back into the engine, meaning it does NOT get cooled via the radiator. This is what allows you to have heat from the heater core, slowing rising in temp, before the thermostat opens. This coolant is always circulating from the pump, to the passenger side block, to the passenger head, to the heater core, back to the pump and repeats. It’s always circulating.
Now, let’s step back and think about the cooling system and how it was designed. In theory all cylinders generate the same amount of heat, and this is a pretty good assumption based on what we are talking about here. So, you’d like the same heat rejection capability at all cylinders. By this I mean you’d like the same volume and flow rate of coolant around the combustion chambers, and you’d like the same coolant temperature around all the cylinders. Heat rejection is controlled by the temperature difference between two “bodies”, the surface area (basically the area inside the head around the chamber where is) and the same flow rate of coolant. If all these are the same then the heat rejection is the same at all cylinders. If the heat generation is the same at all the cylinders, and the heat rejection is the same at all the cylinders, we can basically say the combustion chamber temperature is the same at all the cylinders, and if that’s the case all the cylinders have the same timing requirements. Taking one step farther back from here to help explain this, there are basically four main things that control knock, or detonation, in an engine; Combustion chamber design, cylinder pressure, fuel octane and mixture temperature (there are others, but this is not a class in Internal Combustion Engine Theory, that’s down the hall). The first three are pretty much the same in any given engine at any given time. Meaning, from cylinder to cylinder how much of a difference is there in chamber design, none, how about fuel octane, none, how about cylinder pressure (we are going to say none for right now) but what about temperature?
Ok, before I get too far along this path, and we will come back to this, let’s go back to the cooling system. If coolant wants to take the path of least resistance the passenger side of the motor has coolant flow like this; From the water pump into the block, from the block into the cylinder head, some coolant at the front of the motor goes right to the water cross over, and the coolant at the back of the motor goes through the heater core. There is a flow path out of the front and back of the cylinder head. This is good. What about the drivers side cylinder head?
It goes in at the same place but on the driver’s side. But there is no flow path at the back of the cylinder head to promote coolant flow to the back cylinders. The only way coolant gets to the back of the drivers head is from staggering the size of holes in the head gasket. Now what happens even if this works? Remember a few paragraphs up talking about heat rejection and one of the main factors is the temperature difference between what you trying to cool (the cylinder head) and the coolant that is doing the cooling? Well, if you do get good circulation via this hole staggering all that hot coolant from the back of the cylinder head, has to travel through the head back to the water crossover up front. But this coolant is already hot. It can’t absorb very much heat if it’s already absorbed heat from the rear cylinders. Assuming that the coolant that went through the head gasket openings at the front of the head did its job, most likely this coolant is going to heat these combustion chambers up, rather than cool them down, since they were already cooled off once.
At this point you can see the need for a way to open up the back side of the drivers cylinder head for a coolant flow path, to allow coolant to flow out. This accomplishes two things; one is to open up a flow path to allow more coolant to the back of the drivers side cylinder head, and two, prevents any hot coolant from going back across the front cylinders on the drivers side, possibly putting heat back into the combustion chambers.
This is what the cooling system mod is all about. Adding in a flow path out of the back of the driver’s side cylinder head.
The next obvious question is what vehicles should have this done and why.
As a purist I think every engine should have this modification. It allows you to run more timing and/or leaner A/F ratio with cooler combustion chamber temperatures. In reality it’s not necessary on a naturally aspirated vehicle, unless you want to run pretty high compression ratio. Even though you could argue that this isn’t true, I’m going to at least put it out there; You have to assume that Ford designed the cooling system correctly for a stock vehicle. I think in most cases this is true. But, when you start making a lot more power, like a supercharger, nitrous, things like that, you are making more heat. The engine was NOT designed to handle this kind of heat rejection. How many power adder guys here have either melted a spark plug on the drivers’ side, or blew a ring land on a drivers’ side piston? I bet most of these failure are cylinders 7 & 8 as well. More power is more heat in the combustion chamber. (As a Band-Aid, our software can retard spark on individual cylinders to help some of this, but this is just masking the bigger problem).
Here are some things to think about for the tuners and the engine builders on this board. Knock, or detonation can be broken up into many different types, but I only want to split them into two for now. One is when there are all the cylinders knocking. This is a very loud, very clattery sound of detonation. For you older racers, this was what GM vehicles sounded like the late 70’s early 80’s. Then there is knock when you only hear a few knocks every now and then, or only one cylinder knocking, and it’s no where near as loud as the continuous knock. This is the sign only one or two cylinders are knocking. In this situation, probably 9 out of 10 times the cylinder is on the driver’s side. But, you can’t let the engine go out the door like this, so you have to take timing out. This change/modification will solve this knocking problem. In fact, it will solve it enough that you can most likely run more timing in the engine than you were before, which is be more power.
I want to add a few more comments; I know this is a lot of information to absorb. The current way people are doing this mod is to direct the coolant that is coming out the drivers’ side head, into the tube under the intake. This is done via some Y fitting. As a purist this is going back into the engine without being cooled. While this is still much, much better than the factory setup, I’d like to see this directed back to the water crossover for circulation into the radiator. I also realize this is not totally feasible in all cases.
Mercury Marauders get their coolant for the heater core from the water crossover. This means they have this problem on both cylinder heads, not just one.
The heat generation will vary some from cylinder to cylinder. The air flow and injector flow is not perfect in these engines. Some cylinders get more airflow and those will be more sensitive to knock.
This is the same concept that NASCAR vehicles use for their cooling systems.
Both 2V’s and 4V’s will benefit from this problem. 4V’s have more problems getting coolant around the two exhaust values and cooling them, so they benefit more. But, any 400+ RWHP 2V can and will benefit from this.
Why the cooling mod is important
Originally Posted by Dennis Reinhart
