yes there is always unburnt stuff in the exhaust, but everything that is in the exhaust, everything that got past the valves and the rings, has already seen the combustion chamber. of the exhaust itself, the most you are getting is carbon, the same carbon thats been building up in engines since henry ford put his first together. I understand what you are saying about it all being re-introduced, but I still say that more of that "gunk" is going to come from parts wearing out that would be there regardless. what about all the stuff that the pcv valve lets into an engine? (and If you do some searching on here, I can't remember the last time someone mentioned replacing a pcv valve when doing a tuneup.)


its correct that egr's sole purpose is to reduce NOx emissions, and there are engines out there that don't need them to pass emissions, just like how smog pumps are now a thing of the past. however in GM's first W/O EGR, the LT4, had some extra overlap at the end of the combustion cycle, essentially a built in egr system.

and urea is completely different, it is introduced into the exhaust and reacts with the exhaust there. the engine itself never see's it.

and i'm sorry but one part that you are dead wrong about is about higher compression. NOx is formed because of high heat and pressure. the inert exhaust of EGR cools and slows combustion. higher compression raises NOx emission.

BTW, i'm not trying to sound like I am trying to argue just to argue or anything, but vehicles are engineered to work as a system. and if you change part of that system, you change how everything works together, good or bad. just like how big-tire-bob needed to swap gears after installing a set of 44's. its built to work together. and if you take care of it, it will work for a long time. not to mention all of our trucks are ~20 years old with more than 100k, a bit longer than they were designed to last...considering they were designed by a group of people that had to meet XYZ requirements as cheaply as possible.

 

i think this is evidence that we agree, even if its only to an extent, that the egr is harmful to engines. i already said gunk buildup occurs from normal use, and excessive wear. as a motor ages, the normal blowby of valves and rings worsens and accelerates the rate at which the rest of the motor becomes caked. and as the gunk builds up on valves and rings it becomes harder and harder for them to keep the compression where its supposed to be (in the combustion chamber), and the gunk from going where its supposed to go (out the exhaust). the largest point i was/am making is that the egr intentionally circulates the gunk into the intake tract that would otherwise take an engine's lifetime to occur naturally (non-egr). gasoline AND oil has come a long way since the days of even our fathers. the natural "gunking" of a motor to the extent that it in and of itself becomes a hindrance on performance and a threat to longevity takes much longer today than it did even 20-30 years ago.

in a nutshell, the gunk itself can cause blowby past the rings, and especially valves. this, in turn, allows more gunk to blowby the valves etc etc etc. valve blowby ruins valves/valve seats not only by the abrasive effects of the carbon itself, but the heat/pressure being blasted past them wears them away and burns them up.


while i wasnt specific to gm's factory lt4, i did indicate that cam's with increased overlap and duration cause egr cycle's of their own. it cant be denied that you have a plethora of knowledge on the topic.


its injected to reduce NOx in place of a damaging egr cycle. yes, im aware that its called "diesel exhaust fluid" and reacts with it post-motor. my point had nothing to do with where it was introduced, but that it's being used because the egr cycles were too damaging to a motor that should otherwise outlast the truck. so, it says a lot that engine/truck manufacturers added an additional "fuel tank" that requires special filling stations or stores for refills (not exactly convenient) just to reduce/eliminate egr systems.

higher compression reduces hydrocarbons, CO, and IIRC CO2. not only does high compression inherently reduce the formerly quoted emissions, higher octane fuel contains less of the contaminants that cause the emissions than lower octane fuels. ive always found NOx to be comparable between a properly tuned high compression motor vs a properly tuned low compression motor, but i wasnt specifically suggesting that high compression automatically reduces NOx, but that high compression helps motors pass emissions that otherwise wouldnt pass or would have a hard time passing. it was a side-note to passing emissions with performance vehicles. it has been, however, argued by many that NOx is reduced per gallon burned by high compression motors. high compression motors have a higher thermal efficiency rating, yielding better mileage. it could be quite possible that a high compression motor, while emitting more NOx by volume, emits less NOx in a vehicles life vs a low compression motor that releases less by volume but burns more fuel.

im not trying to argue either. besides maybe a sentence or two, i havent sensed that you have been argumentative at all. yes, the engineered systems are designed to work a certain way, but you also have to examine why. just because theyre factory doesnt mean they are automatically designed to be the best. in fact, its always the contrary (especially as of late). cost of production/manufacture is huge in this equation, and so are government regulations (emissions requirements). manufacturers find a compromise between cost, meeting EPA standards, and performance that is acceptable to them. could they make them better? damn right! . . . and basically everything can be "redesigned" to work better with competence and the right tools. just like modifying the tires on big-bob's truck made it run horrible, a simple gear swap made it "best of all worlds" according to big-tire-bobby. something as simple as head porting and polishing of combustion chambers help reduce emissions but you'd never see manufacturers doing this. i'd also never suggest that egr equipped vehicles couldnt last a long time. just like smokers dont automatically die young. . .but the performance and longevity is definitely effected by egr.