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So...Never used Cometic before but due to my setup thsee were the best ones I could find so this post isn't about trying to find alternative gaskets. My question is has anyone ever used these and it cover some of the water jacket? These had to be made to order so I'm not sure if something is wrong or not but it just didn't look right. What do you think?
Top view. See the offset
Side view of offset. Each arrow indicates where the hole is for the gasket and block
Fel Pro head gaskets cover some of the passage, too. This question comes up quite often and folks have posted that the passages in the heads and block are that large for casting purposes and the gaskets are supposed to block off a portion of the openings for proper coolant flow.
Fel Pro head gaskets cover some of the passage, too. This question comes up quite often and folks have posted that the passages in the heads and block are that large for casting purposes and the gaskets are supposed to block off a portion of the openings for proper coolant flow.
Fel Pro head gaskets cover some of the passage, too. This question comes up quite often and folks have posted that the passages in the heads and block are that large for casting purposes and the gaskets are supposed to block off a portion of the openings for proper coolant flow.
That was the conclusion I came up with after finding out that this wasn't the only type of gasket that partially covered it. But I agree, I believe it has to do with proper flow. Too much flow may not cool properly or at least that's my opinion. But either way the heads are on and they're torqued to specs so I'm rolling with it lol
I don't think it is less flow; it is flow in the proper direction. Restriction is some spots directs flow to other areas, maybe for uniform cooling? It would be interesting to see what happened if the gaskets were cut to fully expose the openings. I'm not gonna try it, though.
Allowing more flow in one spot likely decreases flow elsewhere. In that respect, more is not always better.
It makes sense that the factory would tweak the flow distribution by changing holes in the gaskets instead of changing the block casting. But do the Cometics match the factory gaskets in this respect?
Allowing more flow in one spot likely decreases flow elsewhere. In that respect, more is not always better.
It makes sense that the factory would tweak the flow distribution by changing holes in the gaskets instead of changing the block casting. But do the Cometics match the factory gaskets in this respect?
Good question. I've never compared them to factory gaskets. Mine weren't factory when I replaced them with these. Probably could Google some images and compare the two.
On felpro gaskets i have seen these holes break and allow more flow which didn't result in over heating or any other problem. That is why i am asking. Still confused why and has anyone ever opened them up? I brought this up with a engine builder he couldn't say why or why not other than that is the way the parts are made.
Those gaskets are normal, the design makes sure that there is enough coolant flow to the rear cylinders where it then goes up into the cylinder heads, where it then flows forward thru the heads and then past the thermostat into the radiator. if those partially blocked holes are opened, there possibly could not be enough flow to the rear of the cylinders and back of the heads.
The casting holes are shaped in part to make clearing the sand cores easier at the factory. The gaskets are fine. Cometic says to use very smooth surfaces and put them on "dry." Many users insist that they should be sprayed with K&W Coppercoat, etc. I waffled on that choice, and finally did spray them. They are working great, about 11:1 compression.
For the same reason that a thermostat or restrictor disk helps with cooling. Heat transfer from cast iron to coolant takes a finite amount of time. This is called heat transfer rate and is measured in BTUs/second/degree or similar units. The fewer the seconds the coolant is in contact with the metal, the fewer BTUs get transferred to the coolant. Obviously, there other considerations. If the flow rate is so slow that the coolant never gets to the radiator, that causes heating to go up. This is an engineering tradeoff between heat transfer surface area, flow rate, radiator size, etc.
For the same reason that a thermostat or restrictor disk helps with cooling. Heat transfer from cast iron to coolant takes a finite amount of time. This is called heat transfer rate and is measured in BTUs/second/degree or similar units. The fewer the seconds the coolant is in contact with the metal, the fewer BTUs get transferred to the coolant. Obviously, there other considerations. If the flow rate is so slow that the coolant never gets to the radiator, that causes heating to go up. This is an engineering tradeoff between heat transfer surface area, flow rate, radiator size, etc.
Joe if that was totally the case then the removal of a thermostat would do what.Run cooler.
Joe if that was totally the case then the removal of a thermostat would do what.Run cooler.
That's not what I said. The restriction from the t-stat (or a restrictor disk in it's place) usually is necessary to slow down coolant flow for optimum cooling. Of course, this is COMPLETELY dependent on the particular car, the particular engine, the particular radiator, etc, etc. There are too many variables to make a definitive statement.
Joe my way of thinking restricted water creates heat the the T stat opens and then the coolant flows at a steady rate. This maintains a steady temp. Now with a T stat removed it takes more time to heat up but will. Now it is still not clear what would happen if these holes were opened up. Why i think is no one has done it and accept that this is the way it has been done. Racers have removed T stat's several have told me. They say cooler temps. Now for engine runs of longer time not sure but in the winter time you will freeze your rear end off with a heater on and it doesn't defrost worth a damn.
Once the engine reaches operating temp, the t-stat is fully open and only acts as a restrictor. There are aftermarket washers that can replace the t-stat and simply act as a restrictor. These are available in different hole diameters to allow one to "tune" the flow rate in the cooling system. The experience of racers dealing with cooling a quarter mile at a time is really unrelated to how a cooling system works on the street over a much longer period of time, especially without knowing comparability of heat generation, radiator size, etc.
If you opened up the gasket holes, I think you would need to measure the temperature at multiple sites within the block and heads to see what the localized temperatures are. Measuring at the factory gauge location (one point at the front of the intake) would likely give an "averaged" reading and not represent what's happening at the various spots along the coolant pathway.
For the same reason that a thermostat or restrictor disk helps with cooling. Heat transfer from cast iron to coolant takes a finite amount of time. This is called heat transfer rate and is measured in BTUs/second/degree or similar units. The fewer the seconds the coolant is in contact with the metal, the fewer BTUs get transferred to the coolant. Obviously, there other considerations. If the flow rate is so slow that the coolant never gets to the radiator, that causes heating to go up. This is an engineering tradeoff between heat transfer surface area, flow rate, radiator size, etc.
As the coolant remains in contact with the metal, the instantaneous heat transfer rate will continually decrease because the difference in temperature between the two decreases. In addition, the heat transfer rate of the system slows down because the mass flow rate decreases (this is all basic q=m*c*dT stuff).
Localized pressure control (hydraulic design) with orifices is not there to "slow the coolant down". Nobody slows down flow in heat exchangers to improve the heat transfer rate. You want a turbulent boundary layer to also provide mixing, and the Nusselt numbers will show you that.
I hate seeing wrong information perpetrated, but I'm also sick of fighting over it. The EMP/Stewart website has excellent free technical articles on engine cooling for those that want to learn more.
December 8th, 2016, 10:24 AM
