Exhaust Pressure Testing

[engineermike]

Did it affect flow/ restriction?

I haven’t measure backpressure yet, but the h-pipe is supposed to help with backpressure since the flow pulses can even out. Even when I do measure backpressure it won’t be a good comparison because I raise the boost another 2 psi and in flowing 7% more air now.

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[engineermike]

And now a 36” helmholtz resonator…might be tough to fit two.

 

[n2ofusion]

@GregO I just welded in an H pipe a few inches upstream of the stainlessbros resonator/muffler. Man, what a difference in noise level, especially at heavier throttles. Thanks for the suggestion!

it got a lot quieter? How’s the burble and crackle type sounds? I’ve debated trying to add an X before my center resonator but not sure what to expect sound wise from the extra cross flow

 

[engineermike]

Much quieter. Seems like the burble and crackles are toned down a bit too. Honestly I liked the tone better without the H but it was just unbearably loud.

 

[n2ofusion]

Much quieter. Seems like the burble and crackles are toned down a bit too. Honestly I liked the tone better without the H but it was just unbearably loud.

Good to know. Thanks for the feedback as I’m looking at a very similar setup but worried about losing some of the more interesting characteristics of the exhaust note

 

[GregO]

And now a 36” helmholtz resonator…might be tough to fit two.

Speaking of Helmholtz, I'm intrigued by this tight clean layout and wondered about available real estate above the muffler case and trunk floor.

 

[engineermike]

GregO what brand are those? That’s a smart design.

The stock 2018 mufflers have a hump on top too, just not that big.

 

[GregO]

GregO what brand are those? That’s a smart design.

The stock 2018 mufflers have a hump on top too, just not that big.

https://longtubeheaders.com/product/ford-mustang-gt-18-20-scorpion-axle-back-exhaust-system/

A few 45's some blind caps and you're off and running.
I forgot about the 2018 non valved muffler humpback design.

 

[GregO]

So @engineermike are you rethinking your Helmholtz design and packaging after seeing the LTH mufflers ?

 

[engineermike]

So @engineermike are you rethinking your Helmholtz design and packaging after seeing the LTH mufflers ?

I considered making the bottle type resonator before making the branch pipe. The mechanism by which they function is totally different. Ultimately the branch pipe was easier to calculate and fabricate so that’s what I did. It cleared up a 60 hz resonance but I think I tuned it to too low of a frequency, resulting in a large peak around 200 hz. Since I have a band couple at about the 12” mark, I can easily make a shorter version and clamp it on. I’ll try 24” next vs my 36”. This makes me appreciate the factory reactive muffler designs more. I’ve also linked a great article that makes all this easier to understand.

https://www.enoisecontrol.com/wp-co...engine_exhaust_sound_control_barrier_wall.pdf

 

[engineermike]

It would appear that adding a side branch resonator with straight-through packed (absorptive) mufflers is the best combination of low and high frequency reduction and neither add any restriction.

https://www.enoisecontrol.com/wp-co...engine_exhaust_sound_control_barrier_wall.pdf

The stock muffler is reactive and could probably be made to appropriately have very low restriction but they’re quite a bit more complicated to design and build.

 

[Brad1810r80]

I have magnaflow competition catback with LTH catted long tubes. I added total flow 645 mini mufflers to replace the factory connect and kill some of the drone. They work perfect for it.

 

[mangosmoothie]

Not my car in the pic, but same thing. I've got 3" LTH necking down to the factory 2.25 then to a 2.5 catback.

what do you think it would do if I had cutouts installed where I circled so it's just a straight shot out after the collector when they're open? this seems like it would alleviate all the pressure and is still far ish enough away from the collector for some sort of scavenging.


Do we know if pipe size plays as much of role of we're running LTH? Could the whole system pressure just be lower so the gains aren't as amplified?

edit:

Found someone with boost cutouts did what I was thinking. Looks pretty cash money

 

[engineermike]

what do you think it would do if I had cutouts installed where I circled so it's just a straight shot out after the collector when they're open?

That would likely drop your backpressure down to near zero. Just a word of caution….Ford has something called “blowthrough logic” in the pcm and a patent on matter. The idea is that when intake manifold pressure is higher than exhaust manifold pressure then the air charge can pass through the cylinder during overlap and dilute the exhaust, causing a false lean signal at the o2 sensor. This causes the system to react by unnecessarily adding fuel and running rich even though the wide bands read where they should. The logic is disabled in the GT, GT500, and Whipple tunes. Even if it were enabled, it wouldn’t be calibrated correctly for open exhaust

Do we know if pipe size plays as much of role of we're running LTH? Could the whole system pressure just be lower so the gains aren't as amplified?

LTH wouldn’t affect the flow rate sent downstream to the rest of the exhaust, so pipe size and muffler choice is still just as important. LTH can’t possibly reduce the “whole system pressure” because they’re on the wrong end of the system to be able to do that.

 

[mangosmoothie]

Here's what you measured.

"I deleted the 2.25” factory connection and replaced it with 2.5”. That dropped the post-cat pressure from 6.5 down to about 4.5 psi. Upstream of the cat measured 9-10 now, down from 11 with just the cat-back upgraded."

So as said, you saw a 2 psi reduction from deleting the 2.25" section. Is that going to be a constant 2 psi regardless of how efficient the system is before and after it? Or is it a percentage?

then you said "So between a pair of 60 deg bends and the 2.25” factory connection I’m losing 4-5 psi, which is hard to believe"

So if I'm understanding correctly, doing dumps would give me ~4 psi of benefit (minimum) so I'd get the 10 hp from pumping efficiency from the 4 psi (+ more because I'm a centri car) + whatever added timing the ecu will allow which could be 1* which is potentially another 10 hp.

So there's potentially a 20+ hp gain on the table from having dumps there. I see no downside here. I keep my quiet 2.5" exhaust when I want, and actually get a measurable performance benefit with dumps open (unlike just noise with the factory AE)


Now onto the tuning thing....... I'm confused. Are you saying that if I were to open dumps.... boost would blow through on overlap and dilute the exhaust gases causing a false lean reading, and the car would try to correct it by adding more fuel?

And ford has logic to combat that, but it's turned off, and wouldn't work correctly for open dumps anyway?

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