Exhaust Pressure Testing

[engineermike]

This might be an option. It’s described as a turbo muffler but a jeep guy showed the 2.5” version and it’s straight through and maintains 2.5”.

https://www.jegs.com/i/JEGS/555/30345/10002/-1

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[GregO]

This might be an option.

Jegs doesn’t list the manufactures name. The 3.0” is probably the typical expanded connection 2.5” core.
I reached out to Stainless Bros. yesterday questioning the actual ID dimension of their dual/dual. Waiting on a response and then I’ll pass it along.

 

[GregO]

@engineermike PM sent.
Stainless Brothers responded.
3.00” OD through the body.
5.04” center to center.

 

[engineermike]

Folks, I decided to add another tap after the resonator just to ensure the true 3" part of the system (mid-pipes and mufflers) is sufficient. I relocated the passenger's side pre-cat pressure to just behind the resonator.

This is where it gets weird.

All taps are driver's side now:
Purple - just before the driver's side cat
Gray - just after the driver's side cat, but before the s-bend
Red - just before the resonator
Blue - just after the resonator

At first I thought it was a fluke or perhaps some wiring faulted, causing the signal to reverse. However, I repeated the measurement several times, and even moved the tap to verify it was still reading positive when it should. The readings are valid.

 

[engineermike]

I went back and applied a velocity head correction to all of my numbers, then summarized below with the backpressure added by each component:

Cat converters - 3.0 psi (average of 7 data points)
S-bend between cat and resonator (with 2.25" bottleneck removed) - 2.8 psi (average of 5 data points)
Magnaflow "3 inch" resonator - 6.0 psi (average of 4 data points)
Magnaflow 3" resonator-back piping + mufflers - <0.5 psi (3 data points)

Every 5 psi is about 15 hp loss just due to pumping, plus tech papers suggest you can add about 1 deg of timing for every 5 psi backpressure reduction.

 

[80FoxCoupe]

I went back and applied a velocity head correction to all of my numbers, then summarized below with the backpressure added by each component:

Cat converters - 3.0 psi (average of 7 data points)
S-bend between cat and resonator (with 2.25" bottleneck removed) - 2.8 psi (average of 5 data points)
Magnaflow "3 inch" resonator - 6.0 psi (average of 4 data points)
Magnaflow 3" resonator-back piping + mufflers - <0.5 psi (3 data points)

Every 5 psi is about 15 hp loss just due to pumping, plus tech papers suggest you can add about 1 deg of timing for every 5 psi backpressure reduction.

Great info, thank you!

 

[GregO]

Magnaflow "3 inch" resonator - 6.0 psi (average of 4 data points)

How is the MF resonator constructed internally ?
Looking as though the Stainless Bros. dual in/out is worth a try ?

 

[engineermike]

How is the MF resonator constructed internally ?
Looking as though the Stainless Bros. dual in/out is worth a try ?

It’s actually 2.5” inlets/outlets that comes with their 3” cat back system. It swages up to 3” just downstream of the resonator though. Inside, it’s 2.5” perforated core with an x-pipe. I am told that their 3” version actually turns to a single 3” pipe for some internal length, which might be worse.

The stainless bros looks like the best bet for an upgraded true 3” resonator. I’ll order one soon. The problem is where do you stop? Because the s-pipes are adding 3 psi so you might as well upsize them to 3” too.

 

[GregO]

The problem is where do you stop? Because the s-pipes are adding 3 psi so you might as well upsize them to 3” too.

Horsepower is where you find it, and you just found some.
Where do you stop, do the 3.0” upgrade from cats to MF axleback and then decide.
I couldn’t leave that power potential on the table knowing the MF resonator is killing it.
Personally, I have serious reservation with traditional style X-pipes in high HP applications. Now properly sized oval sweep X-Style is another discussion.
High Horsepower = Size on Size H-crossover or straight piped if you can tolerate the sound of true dual 90° crankshaft V8’s….. yuck !

Thanks for sharing your results. This is really good stuff.

 

[engineermike]

I tend to agree regarding the x-pipe. If you take a cross section right at the “waist” it looks pretty small and 100% of the gas has to pass through that choke point.

 

[GT 550]

The problem is where do you stop?

Indeed!

I guess it's just cost/benefit. Is the hp that could potentially be gained worth chasing given the car's intended usage?

It seems - based on 5hp/15psi - there's about 30ish hp and some timing that could be gained if all pressure could be eliminated but that's not possible. Maybe only a hub dyno run and/or tune will prove whether the numbers carry through into practice.

It might be worth, for academic purposes, replacing the resonator with straight through 3" sections and running it up to see what really happens. Maybe even before buying anything else.

Just my 2c.

 

[MKL_DS]

I tend to agree regarding the x-pipe. If you take a cross section right at the “waist” it looks pretty small and 100% of the gas has to pass through that choke point.

This looks better than most x pipes. More of a chamber with 4 in/outlets than a traditional X.

https://www.holley.com/products/exhaust/x_pipes_y_pipes_and_h_pipes/x-pipe/parts/11437HKR

 

[Brad1810r80]

How about this?? This is what I'm going to try.


MagnaFlow 12599 MagnaFlow Performance Mufflers | Summit Racing

 

[engineermike]

How about this?? This is what I'm going to try.


MagnaFlow 12599 MagnaFlow Performance Mufflers | Summit Racing

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.

 

[ramirj2]

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.

Interesting!

I'm running 1 3/4" LTH with a Corsa 3" double x necking down (2.25") to stock pipes with GT500's mufflers.
At 15 psi (3.25" on a gen 2), I'm not getting the results I expected.
Increasing boost will probably put me on the border line level to experience head lift (stock head bolts at the moment).

I'll put some head studs and CAMS while I'm there, when available.

Got a 3" axle back to install (no 2.25" bottlenecks anywhere) and now I'm wondering;

Would changing from 1 3/4 to 1 7/8 LTH have any benefit?

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