I have been doing research and I saw this brought up a few times. From what have gathered from research is that an idi will run like crap if you coat the inside of the precups but what if someone took the precups out and coated the head side of the precup? That would possibly keep the heat out of the cooling system and in the cylinder without sacrificing how it should run. This could also help make more power due to that fact since more of the heat is in the cylinder. But the biggest benefit would be keeping the heat out of the cooling system. What do you all think? Would there be any negative consequences to doing this?

 

Interesting thought. You'd have to make sure the seating ring for the precup was completely clean, but it may work.
Why exactly would the engine run poorly with a coated cup, though?

 

Cooler temps = less efficient atomization, perhaps delayed ignition?

Honestly, though, I'd be surprised if it made much difference at all, no matter where you put the coating. Remember, the fire starts inside the precup, then swirls out to the rest of the cylinder. So you'd be getting heat from inside it, at least.

My uneducated guess is that a simple coating is A, not required and B, not going to affect things, simply because of all of the metal around it which will allow heat to transfer back and forth.

 

I'm not exactly sure. I'm not sure if the smoother surface doesn't mix the fuel and air as well or what else it could be. Another thing I read is that the fuel doesn't atomize quite as well without the precup retaining heat like it would if it was metal. I def think that coating under the precup would help with that.

 

I have looked at a few different styles of combustion chambers for both IDI and DI diesels, and there seems to be a couple common themes- Generally, if the injector comes straight into the chamber, aligned with the exit, and there is nothing in the middle of the chamber to break up the flow, then the chamber works by atomization. If the injector comes in at an angle that does not line up with the exit of the chamber, then it works by sheet flow, where the fuel actually flows around the wall of the chamber in a sheet of fire. This style is less sensitive to spray pattern, and seems to actually put less heat into the surrounding metal. A ceramic coating still wouldn't hurt, but I don't know how much would be gained. Maybe a build like one of Justin's limit-reaching engines would benefit from this, but I don't know if a noticeable gain would be had in a regular truck. The money may be better spent coating the pistons. Coating the lower cups wouldn't have much if any effect as it sees heat on both sides.

As a side note, in looking this whole thing over the last couple days, these engines combustion chamber and piston design look amazingly similar to the Nissan SD33 that International used to use in the Scout. I have to wonder if International ripped this design off wholesale when they started building their own engines.

 

Harry Ricardo designed the most commonly used pre-combustion and swirl chambers, a design he dubbed the "Comet". I'd wager to guess 90+% of IDIs have this style since it worked so well for atomization and power. Mercedes, GM, IH, VW, and many others used this design.

 

He is mostly credited with creating the swirl chamber, but not really a specific style, and there are many different styles. Varying the throat size, angle, injector angle, glow plug angle, etc can make a difference in operation.
On some Mercedes diesels, there is a ball/pin in the middle of the combustion chamber that the fuel hits and is sprayed around to be vaporized. Other designs put the injector across from the chamber, shooting fuel across into it, then it burns back out into the main chamber.

 

Interesting comment, early Nissan diesels had a lot of similarities to some international engines

 

International used the SD33 in the Scout for a few years. I always found it odd that Ford sourced engines from a company that never put their own diesels into a pickup-