I had a really bad streak of black smoke when trying to climb the rocky mts. And I had low boost. I was only getting like 5psi and was leaving a super thick dark trail of black smoke, and EGTs were flying up. This was when I was at a mile elevation and higher. Before that the low boost wasnt an issue and I wasnt flooring it at all anyway. So I had to down shift and slow to 40MPH to stop that, and I was running with just some junk in the bed, nothing heavy.
Before this the truck ran great and never had an issue hitting 17psi even with the GM4. So when I got where I was going I had ripped off the Banks 3.5" exhaust with Cat included and straight piped it. Truck came alive then, saw 12psi on acceleration now, but was extremely loud, so I put on a chambered 4" muffler and lost a couple psi boost, and it was still loud.
On the way back over the mts it was much better, but I still got more smoke on acceleration at a mile high, even on light acceleration, it just wasnt prolonged smoking. My barometer was reading correctly, and I would stop and start the engine and it didnt adjust enough I guess.
So the ATT requires much more exhaust flow to work well, compared to a GM4. However my backpressures were around 28psi when the GM4 was pushing 17psi and the ATT feel about same power around 15psi and there is only like 17psi backpressure. The ATT uses just like +2psi on the turbine pressure the whole time, compared the GM4 which was always like +5 to +12 psi over the boost pressure. So if the turbo generates all that heat to compress air just 10psi how much work and heat does the engine have to do to compress it to 20 or higher?
I tried my stock and Engh chip and both smoked the same amount up in the mountains.
I need to make a TM and put my GM4 back on with the more free flowing exhaust to make any real comparisons, because with that Cat restriction it must have been hindering the GM4 too, but the smaller turbine would spin up faster.
I still get smoke now when I put my foot into it, even with 5" muffler and 6" tip on the exhaust. Sometimes it fun, but I enjoyed no smoke from the GM4 before. Once I replaced the IP and injectors about a year ago my truck didnt put a bit of smoke out anymore, even with the power chip from Engh, and it gives a lot of power, much higher fuel rates.
