Draconian 5.9 CR Tune :-)

OK let me give a little explanation of what this tune does and why there's a tiny bit of lag.
The vgt on our 4th gen trucks is a very amazing piece of equipment. It has the ability to control the exhaust flow through the turbine side of the turbo. It uses a variable orifice that can change the flow of the exhaust entering the turbo. By altering the exhaust flow two useful things can happen. First by closing the orifice just a little, the velocity of the exhaust flow is increased through the turbine which in turn spools the turbo up extremely fast. Now if the control orifice shut completely, then the exhaust flow is restricted so much that the resulting back pressure will add resistance to the running engine which in turn will try to slow it down which in turn tries to slow your truck down...and walla, you have an exhaust brake.
Those are the good and intended purposes of a normally functioning vgt. Here are the downsides to this...The control orifice is usually run in a position that's no where near completely open position with most vgt mapping except during wot and it may be completely open even then. Two negative things occur from this, both based on the restriction on the exhaust flow. By the control orifice "clamping down" it really muffles the exhaust note coming from the engine and secondly it raises drive pressure or exhaust back pressure during acceleration.
The whole point of this tuning was to setup the vgt so it would function in a fixed open position that would give us maximum exhaust sound and lower our drive pressures just a bit. It does just that! However there is a downside to this as well. The vgt has a really heavy rotating assembly and is slow to spool up without the control orifice speeding exhaust velocity. The results is a very very laggy turbo. However with some tuning magic, we are able to run the vgt set up like this and have it to spool up at a decent rate. It still doesn't spool up instantly like with regular tuning but its certainly livable on a daily driver. The only time I notice the lag on my truck is when lugging the engine in 6th gear. Otherwise it feels completely normal. Wot performance is still the same with this tuning.
Like I mentioned before the sound is much improved! It kinda reminds me of the sound the non vgt 5.9 common rail trucks had hence the name of the tune. Now I will say you will need a full turbo back exhaust to appreciate what this tune does to the sound. Those of you running without a muffler will hear the biggest difference.
And finally the other good thing I have noticed with this tuning are the slightly lower drive pressures. I used to see dp/bp ratios as high as 1.4:1 with regular tuning and now they are anywhere from 1:1 to 1.2:1 with this tune.
Almost forgot...the exhaust brake still functions normally with the 5.9CR tune.
Personally I love this tune for its sound. I was willing to trade a little turbo lag for the sound. Now I do realize that some people won't and that's OK. It's certainly our customer's choice whether they want this.

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