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Pre Cups

My drunken rant... PSN guys and their blah blah blah......I've read too much of their bs and how "junk 6.5's" are .. this and that.... Pffffffft
 
The thread has some good points.

Interesting point on ceramic coating the cups.. Me thinks it would not be the right thing to do as well.

I can't help but think there is some additional turbulence happening as the piston approaches TDC, like some 'reversion' in and out of the cup opening. A whoosh of super heated air.
 
I also read the entire post, I don't agree with the thought about not ceramic coating the cups, I think it would he;p move the heat and or flame while helping prevent as much heat soak into the head..... I just coated my heads and coated the entire precup area...
 
This coating I used will reflect heat and slow down the transfer of heat to the head, I hope I don't need to remove the heads for a long time... it is the same coating I use on piston & combustion chambers in turbo, high comp motors, diesel & gas & fuels.. I have seen it stand up to blown nitro motors that are doing a lot more than mine will......

Here is a pick of the cup..

attachment.php
 
been doing some reading on precups/swirl chambers and it seems one of the main functions of the throat of the precup is to absorb heat and retain it to aid in atomazation/combustion as the mixture leaves the swirl chamber. they even talked about it being red hot
 
Best way to find out if it works or not is to test it. I was thinking of having that done but decided to hold off for now.
 
I would think that coating the piston top, face of the head (inside the head gasket opening), the valves, and exhaust bowl and runner would be the areas that would likely be beneficial. Aside from the above mentioned pre cup. Just thinking out loud here, but wouldn't that keep the majority of the heat out of the iron and out to the turbo where it would doing the most good?
 
sshewins said:
I would think that coating the piston top, face of the head (inside the head gasket opening), the valves, and exhaust bowl and runner would be the areas that would likely be beneficial. Aside from the above mentioned pre cup. Just thinking out loud here, but wouldn't that keep the majority of the heat out of the iron and out to the turbo where it would doing the most good?
Click to expand...

That is what I did, (see my build thread with the pics) and that is what I was thinking ....
 
Last edited by a moderator:
interesting I just read an article that stated that the optimiser engines had a redesigned precup/swirl chamber anyone got one to compare?
 
I know for sure going too small on precups will limit what you can do. Can't forget these engines were designed 30 years ago. Like 1970's oil embargo. MPG was the #1 goal. Warranties were 36K at first and to help the reputation extended to 100K.

Many precups are for specific emmision, power, and MPG goals. Then there are the precups that emissions were not a concern for. Lax as emissions were the 1995 valve cover sticker gives a NOx limit rating that the snap test doesn't measure.

I wouldn't pretend that any engineer 30+ years ago knew 100% of what was going on. Ceramic coating wasn't available. Even now the engineers can miss the boat and land in the water. Just look at the restrictive 6.5 turbo or the LLY turbo restrictions/running hot. The 6.5 had to be redesigned to fix the cracking issues GM/Detroit Diesel couldn't figure out. Technology has come a long way since the 6.2 was designed and built.

Then the bean counters get involved and substitute a cheaper crankshaft than the original design. So even if the engineers could do better - cost could have stopped them.

If you get through that a production tooling error clipping the block caused cracks... 99 Dodge diesels suffered cracking from a core shift in casting...

Reworking them for power requires new out of the box thinking. The 6.5 TD design missed the boat for both MPG and power. It isn't till you correct some serious design compromises that you overcome them.

The good news is the 6.5 is still a production engine for the military. Advances/experimental success made can have a market for the military...
 
You know what would be really interesting and perhaps educational? Taking a pre cup from each phase (square, diamond, etc...) and cutting it in half, much like 6.2 did with the pistons. That would give us a cross section of each's opening and how much of a role they play in figuring CR, swirl paternal, etc...

To be honest, I'd like to do that to a 6.2 and a few 6.5 heads. That way we'd know just how far we can push opening up the runners. For those of us wanting to get the most out of porting and polishing.
 
sshewins said:
You know what would be really interesting and perhaps educational? Taking a pre cup from each phase (square, diamond, etc...) and cutting it in half, much like 6.2 did with the pistons. That would give us a cross section of each's opening and how much of a role they play in figuring CR, swirl paternal, etc...

To be honest, I'd like to do that to a 6.2 and a few 6.5 heads. That way we'd know just how far we can push opening up the runners. For those of us wanting to get the most out of porting and polishing.
Click to expand...

you'd need to cut the heads because the precup is only 1/2 of the system the swirl chamber is cast into the head.
 
so after doing a bunch of reading this is the theory I came up with. enlarging the hole will help as long as the boost pressures are higher otherwise you lose the turbulence it needs to atomize the fuel . I think you could get to the point that you would lose your bottom end and only have top because of the lack of boost. so if a guy really wanted to push things and still be streetable it would have to be supercharged or a supercharger/turbo combo
 
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