Kreb (Forum Supporter) said:
My general take on the guy is f--k him. Coal Rollers are dillweeds and anyone who aids and abets them are double-so.
But I have a question - do those retunes really produce huge mileage gains like his supporters say? I'd think that rolling coal and efficiency are two very different things.
First, we have to clarify some things (diesel enthusiast myself). The answer is yes and no. A retune for logical use like towing or efficiency is highly effective. A tune to make black clouds is a purposely-invented way to simply make black clouds. It's like a Carlolina Squat or a plywood spoiler on a K-car. It's just for show. Those tunes don't care about MPG, they care about announcing your tiny hootus.
There are many things you can do to a diesel engine for performance. Some of them make some black smoke, some make more power, some make more MPG. Others make huge clouds of black smoke. The thing about a diesel is that it's just air and fuel.
Dad's 04 Dmax has been tuned to make frightening torque... like nearly 1000 at the wheels. In the fifth position on the rotary switch, it does make some black smoke. It's a trade-off of getting enough fuel early to add mass and get the turbo spinning sooner. As soon as there is boost, the black smoke goes away, so it's more like a faint puff instead of an opaque wall of soot. On the #3 setting, it still makes 850 tq at the wheels and there is no black smoke. It also easily puts down 24mpg (up from a factory tune that usually nets 19mpg). So in dad's truck, it has been taken pretty much to the max before coal-rolling and it makes more torque than a saint and gets 20-25% better MPG than stock while doing it. That is a significant fuel consumption difference.
The way you do that is by introducing more fuel and doing it earlier. Factory tunes use conservative injection timing for two reasons: 1) NOx emissions, and 2) noise. Advancing injection timing has pretty impressive effects on MPG because you're making more of your peak cylinder pressures in the critical 12-27 degree ATDC ranges where pressure on the rod has the most torsion on the crank. Factory timing leaves torque and MPG on the table as a trade-off for NOx compliance. Doing nothing but adding a few degrees injection advance can get you significant torque and MPG alone. You can keep going with more advance until you reach a point where the flame front meets the piston before TDC, which not only starts robbing power, but it also tends to make things explode.
The short version is... factory tunes are limited on when they can inject fuel due to NOx, which means your pulsewidth and volume of fuel injected is limited before you cause HC emissions to spike. Advancing the timing lets you inject more fuel since it has a longer time to burn it before the exhaust valve opens.
The other factor at play with MPG is driving style (just like any vehicle). Since most of your driving is "normal," advancing injection timing means you are using more of the BTUs in the fuel you inject (fewer HC out the tailpipe) which means for regular daily driving you're using less right foot to achieve the same motivation. More of the fuel is releasing its BTUs at peak leverage on the crank, so you need less fuel for the same driving style.
Diesel tuners that don't roll coal will carefully advance timing and add fuel to maximize power, MPG, or both. Their point is to NOT roll coal because that is both wasted power and MPG. Dad's 5-position chip is 1) stock tune, 2) towing which adds a small amount of fuel and a couple degrees more advance, 3) economy which adds a bit more advance but no additional fuel, 4) stage 1 race which maxes safe advance and adds more fuel, and 5) stage 2 race which keeps max safe advance and adds as much fuel as it can without spiking EGTs. Coal rollers' tune might be 1) stock, 2) add fuel, 3) add more fuel, 4) add even more fuel, 5) just dump raw diesel in the intake. That's an exaggeration, but their tunes are specifically designed to make clouds.
I mostly explained that because you asked, but also because I am VERY tired of diesel myths and misconceptions. Diesel tuning is one thing. Yokels rolling coal are douchebag E36 M3sticks and deserve all the jail time they can get. I do feel the need to delineate between diesel tuning vs coalies. Coal rollers have tuned their diesels to compensate for their tiny, white-trash hootus. Responsible diesel tuners have optimized their vehicle for power, MPG, or torque for a logical purpose. If you pulled up between a bone stock duramax and dad's hopped-up duramax, you wouldn't know the difference. Its just that people only SEE coal rollers and assume they are the only tuner diesels out there. Dad's is tuned pretty insane and you would mistake it for a stocker so you wouldn't even think it has a tune. People see a coal roller and know it's tuned, so they assume all tuners are coalies.
But if anyone conflates all diesel tuners with coal rollers and brodozers, I tend to get a little defensive. That slippery slope you're all talking about? Responsible diesel tuners like me and dad are the first thing to get scrutinized. Your gasoline motorsport will be the very last thing to get discussed by the EPA, so a little education in the quest for solidarity might be an ounce of prevention.