That gives it a little more rpms to get the turbo (or turbos, does it have two?) online and takes a away some of the lag, though it's still there slightly.
Yes the 6.4 diesel engines are a twin turbo setup. The standard trans versions seem to have less lag in my experience with them.
The biggest issue with removing your cat for more power is that if you have the down stream O2 sensor (the one after the cat) you will constantly have a check engine light and most likely be forced into the base tune causing a reduction in power and efficiency.
Adding a turbo usually means you need a programable ECU and depending on the engine may need a larger injector. You also need to reduce or increase the spark output in some cases because you can get what is called "blow out".
Spark Blow Out:
A very common problem encountered with increased boost pressure is spark blowout. A bit of misnomer, spark blowout isn’t the spark being ‘blown out’, but rather the spark being unable to form. This causes a misfire, or more accurately, a lack of combustion due to a lack of spark. This missed combustion event is very noticeable and can be very unsettling to those unaccustomed to the problem. It can best be described as sounding like muffled machine gun fire, accompanied by a jerky, and quite apparent, loss of power. In the vast majority of cases, spark blowout is non-harmful, albeit very power robbing. Prolonged spark blowout can cause raw, unburned fuel, to wash down the cylinders and contaminate the oil, but usually the issue doesn’t occur frequently enough to be a significant problem. Spark blowout usually occurs at peak torque, when cylinder filling is at peak density. For TD04 frame turbos this usually occurs between 4200-5500RPM.
Blowout is named as such because of the way that a spark forms. When air becomes electrically charged beyond its point of electrical breakdown, charge will leak from the charging conductor into the air. This charge leakage will form a coronal cloud that will propagate from the spark plug’s electrode, until it reaches the spark plug’s ground strap. At this point, a conductive channel will be created and the spark will form. The lack of spark occurs when the coronal cloud is ‘blown out’ and can’t reach the ground strap.
The speed at which the coronal cloud moves is directly related to the power of the spark and the dielectric strength of the medium through which the cloud is traveling. In the case of an engine, the power is the voltage at the tip of the electrode and the dielectric medium is the air + gasoline mixture inside the cylinder. As boost pressure increases, the density of the air and gasoline mixture increases, increasing the dielectric strength and slowing down the propagation speed of the coronal cloud. When the in cylinder density increases past the point at which the spark voltage is sufficient to bridge the spark gap, the spark will not form and blowout will occur.
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