That is correct, stock manifolds and cats but 3" dual all the way with a StainlessBros resonator and Magnaflow mufflers. I also fabbed an H pipe and a pair of Helmholtz resonators. I don't know exactly what the power gains were because this has been a long process and I made other changes along the way. I can say, though, that I'm certain I gained due to reduction in pumping losses and also added spark timing since lower exhaust pressure helps with knock margin. On my last log I was running 17 deg timing at 15 psi (3.375 pulley whipple) and stock 12/1 compression with zero knock detected. The added timing is probably worth more than the reduced pumping losses.
Unfortunately, it didn't turn out that way. Every 2.5" component was adding significant restriction. When supercharged, the entire 2.25/2.5" system needs to be upgraded. The sticking point that most miss is that most "3 inch" resonators are actually only 2.5" internally, so don't overlook this part.
LTH and deleting cats would leave you with the backpressure imposed by my cat back only, or about 2 psi. This would be under 1/2 psi if NA.
I agree. Lingenfelter (IIRC) published many years ago that under 5 psi should be the goal. Once you get there the returns dwindle down to nothing. I even checked this on a dyno some years ago and found it to be true.
The original goal here was to determine how bad the exhaust pressure was and determine the most effective ways to improve it. By measuring the pressure directly, I don't need density to determine velocity to determine pressure. Since I determined pressure at numerous points in the system, I was able to spend my time and money most effectively in addressing them. Since I'm now barely over 5 psi backpressure at 90 lb/min airflow, I am basically done. The only work left to do is to remove some baffle plates I installed earlier to see how much it changes noise and pressure. After that, I'll move my analog inputs on to a MAP sensor in the manifold so I can sharpen up the SD model or perhaps thermocouples in the cat converter to check the cat temp model and COT effectiveness.
Is there an "off the shelf" cat back system that you think would get close to your results with the custom system you've created?
Any cat-back that uses the “factory connect” isn’t going to cut it, since it’s only 2.25”. Also, every resonator I’ve seen doesn’t maintain 3” internally, so it would have to be one with just an H-pipe. Short answer is: no.
Lacking a direct measurement, in order to accurately calculate an ExhMAP, the PCM would need exhaust mass flow, exhaust temp, exhaust composition, barometric pressure, and some representation of the losses the exhaust system imposes. It is known that the PCM has access all of that data except the numerical representation of the system losses. This is really just a single constant, like an orifice coefficient or equivalent area like the TB model. However, I don't see that coefficient or area defined anywhere in my file. I do see where the Ecoboost strategies have the information needed to model the turbine and determine drive pressure, though, and where the GT500 has exhaust pressure limits set up.
Figuring out how much exhaust changes change the restriction was precisely the goal of this science project. Correcting the ExhMAP model would just be icing on the cake if possible.
If calculating exhaust pressure from known parameters, you would certainly need the temperature. But as you know, the calibration has all it needs to determine the exhaust temp already. However, I started out by directly measuring "the answer" that would result from this calculation, so there was really no need to take temperature into account. The whole point was to see how much physical changes to the exhaust system lowered or raised the collector pressure, not to determine mass flow rate or velocity.
I wasn't satisfied with the reference you provided for this correlation between exhaust pressure and timing advance. The paper cited said "Compared to other factors that influence knock, exhaust back pressure does not have as dramatic of an effect, but it is still worthwhile to consider"
The increase in power due to knock margin is a bonus of lowering backpressure, but far from the sole reason. It's tough to find the quality of data you are looking for to prove a side-benefit of the efforts, but I used what I had to get an idea. Anecdotally, you can see that the ecoboost engines run into knock at really low spark-timing in spite of low compression ratio and GDI. One might deduce this to be caused by the high exhaust pressure. Plus as I also said, and unfortunately I can't share much about this, I consult with an OEM engine calibrator who also told me that reduced backpressure increased knock margin in development engines. Whether it's 0 deg, 1/2 a deg, or 2 deg of margin really doesn't make the effort any less worth-while to me, so the exact effects on knock aren't really work arguing over.
It's a fairly common practice to measure pressures in a piping system to determine how much loss there is and where effort should be placed to address it. That's all I'm doing. I can't tell if you don't agree that lowering backpressure is beneficial or if measuring backpressure doesn't tell you the location of the restrictions. What I do know is that piping system losses reduce engine efficiency and I can't think of a better way to identify the losses than to measure the pressures.
I own an ecoboost and your above comment on excessive exhaust backpressure causing knock even at low timing numbers has me interested in your thoughts. I have a 3" aftermarket catted down pipe that I have yet to install since I have been told by tuners that installing it requires a tune to keep the engine calibration running at safe limits.
