So the question is, at the same level of "performance", meaning apples to apples comparisons with regards to the truck going down the road in similar conditions, ie: 55mph-65mph on the same stretch of road with the stock turbo and 3 inch down pipe, the stock turbo with the 38R with the 3 inch down pipe, a stock turbo with a 4inch down pipe and the 38R with the 4 inch down pipe, which would have the better flow or less disruption?

Then we add in the scenarios with a 3.5inch down pipe and those turbos. Then to muddy the waters a little more, we have the fact that I have 160cc/30% over sized single shot injectors and we have a whole different set of variable to add to the equation.

But I would imagine, given the same/similar set of circumstances, the truck would be moving same/similar amounts of air/exhaust through the down pipe so that venturi effects and turbulence effects and expanding gasses would be the same/similar, or am I missing something?

Rich, I am not sure if I really noticed anymore lag, but my transmission isn't shifting right/consistently and hasn't been for a long time now. That will sometimes make the truck feel like it's laggy because it doesn't drop down a gear at the right moment and the torque converter keeps unlocking at certain throttle positions vs. load.

I am in the process of loading the buckzooka for another rebuild or an HD4r100/ or BTS transmission round. I haven't decided which of the three is going to be my route. (I know my preference(BTS) I just don't know if I can justify it financially at this point.)

 

I need to post the video of the external sound, but the drone in the cab is more than I like. A resonator pretty much got rid of it, but that also pretty much killed the whistle out the pipe. I'll say this though - the EBPV is a ton quieter with the resonator.

 

A little OT.....We made our annual spring break pilgrimage to FL in our trusty 2005 QX 56. V8 powered, fuel mileage awful but hey its paid for. A few years back, right before its semi annual emissions test the CEL came on. Lo and behold both exhaust manifolds were cracked. Only parts available at the time were from Infiniti at about 1800 a side. I kid you not. Car had 88K and the emissions warranty had expired at 80K.


Researched online and found Stillen headers for 800 bucks. Our MPG went to almost 14 from 8. The stock stainless muffler was almost rotted through so I bought some cheap stuff off parts geek which was way too small and restrictive. I decided before the trip this year to change that so a week before departure I bought a Gibson cat back system from Summit.


Holy drone Batman!


2K rpm was unbearable! By this time it was Thursday and we were leaving Friday afternoon. I was in a world of caca. I called Gibson and spoke to their tech and came to the conclusion that the system was designed around all 4 cats not two. He suggested a resonator. Found a shop that installed a used Dodge resonator for 80 bucks and it sounded GREAT! It eliminated about 80% of the drone. Round trip to Florida and no complaining from the wife is a good thing. I even got over 19 MPG during the highway stretches!


My point is, I'm sold on the idea of a resonator.

 

Good question. Without having access to the Pinnacle models for for dynamic calculations, I honestly cannot say. For the real world sake of our truck utilization (non-race world), I'm honestly not sure if we could even recognize the differences. I'm sure that the differences are real and that thet can be calculated, but just not sure how much SOP difference there is, if any.


P x V = n x R x T

Pressure x Volume - number of moles of gas x Rankine's ideal gas constant x Temperature

Rankine's ideal gas constant does not change between the compared conditions

HOWEVER....
1) Increase fuel only and you can change Pressure, Volume, Temperature, and number of moles of gas
2) Use a larger turbo without changing fuel, and you might see a change in both Volume and Temperature
3) Change the geometry of the piping, and you could impact the system's back pressure due to increased or decreased flow turbulence, and in turn, that could also have an upstream impact on the combustion dynamics in terms of fuel efficiency, especially if the turbo has more trouble pushing the exhaust flow out of the system.
4) It all begins to run in circles with perpetuating "feedback" from whatever change is made (fuel, air flow, etc.)... delayed feedback due to lagging response on exhaust beginning to impact turbo fan velocity and amount of ingested fresh air, etc.


Now I'm getting dizzy from just thinking through how each change creates a result which then changes the dynamic conditions which the first change was based upon.

 

I did my flow calculations for the 7.3l (an easy to calculate variable) and for that flow at different PSI boost. The rough air flow calculation isn't too bad, it's when you factor in the environment (temperature and altitude) that things get weird. I also made some pretty detailed observations of the truck before and after all of my upgrades. Here are my observations on going from 3.5" to 4" turbo-back exhaust alone:

Doing a WOT run with the 3.5" exhaust, the boost would creep it's way up to 20 PSI and pretty much peak out with the red line mod and no tune. Once I installed the 4", the boost would snap to 22 PSI and park there with the same tuning and mod.

My calculations showed that the flow of the engine at 20 PSI boost is pretty much the rated capacity of a 3.5" pipe with all those bends. Getting in the head of a Ford engineer, it makes perfect sense that they would select an exhaust size that is rated at almost 15% above the anticipated flow of the stock configuration of 17-18 PSI boost at 3200 RPM.

 

The difference between your comments and mine, Rich,are that I was referring to a simple highway run at normal speeds... not WOT. Your WOT conditions will certainly allow you to measure and feel a difference in the exhaust comparisons.

 

When talking sane driving, that's where the drone kicks in... the other observation I made when going to a 4" exhaust.