As you said yourself, "Now if I was on 5, 7, and or 9 CaTCHER level I would definitely have head studs". That indicates, at the very least, you are aware that the HG has issues in certain conditions. Would feel the exact same way if it is was a 5.9? Probably not because the 5.9 did not exhibit that weakness until you went really big constant power, where the 6.7 has exhibited issues at considerably lower power levels. My son has head studs on his 5.9L is was using the Smarty on CaTCHER level 5. Now he is using EFILive. He has already rebuilt the engine with only 26,000 miles on the 2006 truck.
There is enough data to strongly suggest that deleting the EGR uncovers a weak spot in the engine design, predominantly with the stock turbo and the stock HG. Naturally instances of failure are more prevalent with high power and certain tuners, but, there have been instances of stock and lower power problems also. Not as many, hard to compare because driving styles are so different, but the specter is there. I agree but I also think everyone should have gauges installed to what your Boost Pressure and EGT's.
As to why you have ever had problems there is no concrete answer. Luck of the draw, driving style, tune design, etc., are all possible. Does not mean the NEXT guy will have the same results. I try to keep my Boost pressure under 30PSI at all times some times I have almost reached 35PSI when towing in the mountains. I also watch the EGT's very closely when towing staying under 1,000 F. Will manually shift from 6 to 5 or to 4 to keep the EGT's down and the Boost pressure under control.
As tot he why, that is in the design of the engine and the operation of the VE turbo. The 6.7 is built on the 5.9 block with a larger bore. That has considerably reduced the amount of material between the cylinders at the head juncture. The 6.7 is also a Siamesed cylinder design where the 5.9 is not. I am sure you have heard this and accepted it, but, have you really THOUGHT about what it means THEN factored in the over all fueling and EGR operation? YES I have also I am a retired engineer from Cat so I am very fimilar with diesel engines.
Typical fueling tables and engine design is slanted toward stoich rich, the EGR us designed to replace incoming oxygen to limit cylinder pressures and temps. When you remove the EGR effect by blocking it you now have an abundance of fuel AND air which will automatically increase the cylinder temps and pressures without doing anything else. You see this with increase efficiency and mpg as a result. A typical Smarty tune will enhance this effect with timing to increase efficiency and more fuel in the lower rpms putting the TQ peak about 2000 rpms where it is the most usable. Simply by blocking the EGR the whole design has changed to where the conditions for higher cylinder pressures and temps is enhanced, adding in Smarty just enhances it that much more. When I deleted the EGT'S fell off from a stock engine; I am normally lower by 200 to 400 degrees F depending on towing conditions. These temps are from my gauage but this was the same gauge set up for the first 12,,000 miles as stock. This was my baseline for comparison.
Remember, Smarty is NOT changing the base engine operational code, all it is doing is manipulating tables. The base code still THINKS it has all the installed pieces on the engine and is still operating it like an emissions engine. This is where things starting getting off track because there is not good way to manipulate the VE programming and operation, it still works like it did stock. The problem s the tendency of the turbo to shut the exhaust flow way down when lifting off the throttle, it essence is slamming the control down to very small sizes, the minimum on that turbo is 3 cm^3.
We already know the CR fueling system does not chop fuel as soon as the throttle is lifted, the FCA cannot back rail pressure off that fast, etc. So now you have the conditions where there is more air and fuel, EGR is absent for a control medium, and the turbo severely limits exhaust flow. So what happens when you throw a lot of air and fuel into a cylinder that has a restricted out flow? If nothing else we have learned the results of that operation in a diesel engine over the years, sometimes we just don't stop to think about it from that perspective.
Now we have conditions that we have been dealing with for years with few consequences, the 5.9 just does not have issues with this scenario unless it is aggravated to the extreme. The 6.7 is NOT the 5.9, worth saying again, the 6.7 is NOT the 5.9. The why is the block design itself, simaesed cylinders and larger bore on the same block. Larger bore means less material between cylinders for head gasket and more pressure on the head from larger bore. Now the crux of matter, what happens to expansion rates when only 2 sides of a cylinder are cooled? Short answer is they expand at different rates under heat and pressure. What happens to gaskets to a thin gasket when they constantly get pulled and stretched unevenly? What happens to clearances between head and block when the expansion is uneven due to differences in cooling?
The removal and deleting of the EGR has created a perfect storm of sequences that have been proven to cause failures, the big unknown in there is driving style. THAT in itself has some major contributions that simply cannot be quantified and applied to all circumstances. All I can tell you is the mechanics of the failures have been defined and most of the fixes found to counteract the source. I can tell you it is not a myth. I cannot tell you when and if a particular truck is going to have a failure, too many variables to predict it that close.
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