Raise your hand if you've blown up an N54!

[kayzrx82]

I think you may be confused. An insert will only prohibit heat transfer if the coolant passages in the insert cause any sort of restriction to coolant flow. Maybe there is a specific insert you are saying will do this, but I can assure you that there are N54 inserts that are port matched to the passages on the head to prevent this.

What I am referring to has very little to do with the coolant flow ports. If you have a deck insert that isn't matching the coolant ports, that's a whole different problem in itself related to coolant flow and I would not recommend using one that didn't match. Whats lowering the efficiency of the closed deck to transfer heat is that coolant is no longer in direct contact with that portion of the cylinder wall. The heat now has to go through the insert then transfer to the coolant .That top portion of the cylinder wall is the hottest part of the block that is in contact with coolant. When I was building my motor I looked into 3 company's to do the deck. I was familiar with a closed deck lowering cooling ability from a different motor I had closed . 2 of the companies said that it would lower cooling efficiency but upgrading the cooling system would help offset that. They recommended a larger radiator and lowering the coolant temps which will allow heat to transfer faster because of the greater Delta t. The third company claimed it wouldn't have an affect on cooling. When i asked him to explain why that company couldn't. There are deck inserts that are machined out so that it is not flush with the deck height to allow coolant to contact the top of the cylinder. They do not support the very top of the cylinder wall. That design is a compromise between strength and cooling as the top of the cylinder wall is where the highest pressure is and needs the most support, yet that's where the majority of the heat is rejected from the cylinder sleeve to the coolant.

 

[The Convert]

What I am referring to has very little to do with the coolant flow ports. If you have a deck insert that isn't matching the coolant ports that whole different problem in itself related to coolant flow and I would not recommend using one that didn't match. Whats lowering the efficiency of the closed deck to transfer heat is that coolant is no longer in direct contact with that portion of the cylinder wall. The heat now has to go thoughbthe insert then transfer to the coolant .That top portion of the cylinder wall is the hottest part of the block that is in contact with coolant. When I was building my motor I looked into 3 company's to do the deck. I was familiar with a closed deck lowering cooling ability from a different motor I had closed . 2 of the companies said that it would lower cooling efficiency but upgrading the cooling system would help offset that. They recommended a larger radiator and lowering the coolant temps which will allow heat to transfer faster because of the greater Delta t. The third company claimed it wouldn't have an affect on cooling. When i asked him to explain why that company couldn't. There are deck inserts that are machined out so that it is not flush with the deck height to allow coolant to contact the top of the cylinder. They do not support the very top of the cyclinder wall. That design is a compromise between strengh and cooling as the top of the cylinder wall is where the highest pressure is and needs the most support, yet that's where the majority of the heat is rejected from the cylinder sleeve to the coolant.

I'm going to have to disagree with your two engine builders. As you can see in the attached screenshot, aluminum has a FAR higher thermal conductivity than water. So, providing a "bridge" from the hottest part of the cylinders to the outside of the block and to the top of the water jackets should either have no effect, as the head is aluminum, or increase the cooling efficiency. The only thing I can see being "negative" is you would lose a cup or two in coolant volume due to the insert, but I cannot see that mattering.

If I am wrong, by all means, please prove it and tell me why.

 

[kayzrx82]

I'm going to have to disagree with your two engine builders. As you can see in the attached screenshot, aluminum has a FAR higher thermal conductivity than water. So, providing a "bridge" from the hottest part of the cylinders to the outside of the block and to the top of the water jackets should either have no effect, as the head is aluminum, or increase the cooling efficiency. The only thing I can see being "negative" is you would lose a cup or two in coolant volume due to the insert, but I cannot see that mattering.

If I am wrong, by all means, please prove it and tell me why.

View attachment 16164

If we were trying to transfer heat to a heat sink then you would be correct but the heat has to be transferred to the coolant. You have to use the thermal transfer coefficient not the thermal conductivity of the material. The thermal condutivity will tell you how well heat travels through a material. In the N54 there's a steel sleeve liner then an aluminium sleeve then the water jacket. Adding material between this path will slow heat transfer. Thermal coefficient is simply a formula to calculate how much watts when taking into account distance . The thicker the sleeves the slower that transfer occurs. The interface between the coolant and the solid surface is where the thermal transfer takes place to the coolant. You can't just look at a thermal conductivity chart and say that. If that we're the case a solid block of aluminium with fins attached to the block would have superior cooling transfer then a liquid cooled setup. This is not the case. The thinner the cylinder wall the better for cooling system efficiency. It's a balance between heat transfer and strength. As for the companies that agreed with the insert lowering cooling efficiency, I'm not going to name names and get into a he said she said. I've used both in the past for other projects and they are reputable with skilled shops. But the 2 that admitted it does affect coolong are 2 large players in building the N54 engines. There is alot of technical document online concerning open deck and closed deck cooling efficiency. I'm not saying a closed deck is bad. Its needed above certain cylinder pressure to keep the cylinders round . What I'm saying is if you have a closed deck, the cooling needs to be addressed with changes to the supporting hardware and operating points of the cooling system.