Exhaust Pressure Testing

[andrewtac]

I am told by those I trust that this muffler actually turns to a single 3” internally. It’s more of a >-< than an X.

I will be ordering the stainless bros one soon.

In for this, I like the quiet setup I have but want to go 3" for the last little bit of power, while keeping it quiet.

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[engineermike]

StainlessBros resonator came in today. This thing is beautiful and absolutely true dual 3” all the way through. The ends are even enlarged to 3” ID for easy installation.

 

[engineermike]

Length is the same as the Magnaflow 2.5”, at 14”. Inlet and outlet center/center is 5”. Magnaflow is 4.5”.

 

[Andy13186]

Can you show any pics of the inside of this muffler? Did you get this installed yet? Ive been looking for a quiet mid muffler. I tried the magnaflow 12599 which was too big to fit where the OEM resonator goes. Interested to see how it works for you. I was also recently looking at the jegs turbo.

 

[GregO]

StainlessBros resonator came in today. This thing is beautiful and absolutely true dual 3” all the way through. The ends are even enlarged to 3” ID for easy installation.

I like your paper concentric (edit; Ecc.) reducer idea.
SB has their A game on.

 

[engineermike]

Can you show any pics of the inside of this muffler?

I can but post #45 shows it. Not much to see beyond that…it’s two 3” straight through perforated cores. Looks like fiberglass packing.

Did you get this installed yet? Ive been looking for a quiet mid muffler. I tried the magnaflow 12599 which was too big to fit where the OEM resonator goes. Interested to see how it works for you. I was also recently looking at the jegs turbo.

This one is almost exactly the same size as the 2.5” resonator that comes with the magnaflow street series cat back.

I haven't installed it yet because this will be a project making it 100% dual 3”. I need to order a welder….

 

[engineermike]

I like your paper concentric reducer idea.
SB has their A game on. Their Ti exhaust stuff is all the rage.

The paper reducer was to check fitment of the following 4x3 eccentric reducer. Btw making an eccentric cone from paper is harder than it sounds. I suspect the convergent reducer on the cat is causing restriction.

 

[GregO]

The paper reducer was to check fitment of the following 4x3 eccentric reducer. Btw making an eccentric cone from paper is harder than it sounds. I suspect the convergent reducer on the cat is causing restriction.

Nice, you're on the right track.
I've spent a lot of time fitting sanitary butt weld & BPE fittings over the years. I like your style.

 

[engineermike]

This is the resonator that is supplied with the magnaflow “3 inch” street series cat back. It is 2.5” inlet and outlet with an Internal X. It’s next to the stainless bros 3” muffler that is true 3” straight through on both sides. After cutting off the magnaflow and clocking one of the mid-pipe about 90 deg, the STB tucked up quite nicely. Now on to the hard part….

 

[engineermike]

One more…

 

[engineermike]

It was a job, but I got rid of 100% of the 2.5" piping. I cut the convergent cone off the stock cats and installed 4x3 eccentric reducers, followed by a 3" 45 deg dog-leg going into the *true* 3" straight-through dual in/out StainlessBros resonator/muffler, then to the Magnaflow 3" mid-pipes and 3"/2-2.5" mufflers. The sound is beautiful but surprisingly loud considering the car has 2 cats and 3 mufflers.

As far as results go, it looks like it chopped about 5 psi off of both sides. There was a 1 psi baseline offset difference vs the earlier test, so the attached graph shows them normalized to the same zero. The peak on the higher side is just under 7 psi now, vs 12.5 psi before.

 

[Torinate]

That’s a big difference. Interesting that the sound become louder with same cats, albeit flowing better with the modifications you’ve made.
Well done!!

 

[Torinate]

I wonder what this pressure drop would equate to in real world terms as we’ll wheel horsepower. Any thoughts?

 

[80FoxCoupe]

More flow = more volume

 

[engineermike]

I wonder what this pressure drop would equate to in real world terms as we’ll wheel horsepower. Any thoughts?

You gain power from reduced backpressure through 3 mechanisms.

1. Reduced pumping losses. This is the effort it takes to push exhaust out on the exhaust stroke. It can easily be calculated and turns out to be a 3/1 ratio for us: 3 hp for every 1 psi. This is the minimum you can gain.

2. Increased airflow. You wind up with less exhaust pressure in the chamber during overlap so fresh charge can start entering the cylinder sooner. However, this effect depends largely on the induction system. On a high performance NA combo with lots of overlap, the effect can be massive. With a PD blower, the flow is governed by the blower size, speed, and inlet pressure so exhaust will have zero effect on flow.

3. Knock margin. Research papers suggest that every 5 psi allows about 1 deg more timing without knock. For one reason or another I haven’t been able to take advance of this aspect as of yet. The humidity has dropped here which reduces knock margin and can counter-act this effect.

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