Exhaust Pressure Testing

[smokescreens]

Finally 3inch all the way back. Kooks 1-7/8" longtubes. 3inch elbows, 3inch H pipe with stainless resonators and Corsa sport active axle backs.

Is it spring yet?

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[engineermike]

@smokescreens I want to hear.

 

[smokescreens]

@smokescreens I want to hear.

Ok. Let me pull it off the lift

 

[Mike-S550]

Finally 3inch all the way back. Kooks 1-7/8" longtubes. 3inch elbows, 3inch H pipe with stainless resonators and Corsa sport active axle backs.

Is it spring yet?

very nice! Exactly what resonators are those, and can we get video of a cold start?

 

[smokescreens]

very nice! Exactly what resonators are those, and can we get video of a cold start?

Stainless bros, forget the model number but they are the longer version. I think they are 17" long.

Uploading a youtube video now.

 

[smokescreens]

Normal, quiet and track

 

[engineermike]

Man that’s awesome. Do you know how the internal passages in the muffler are? In quiet mode is it still 3” all the way through?

 

[smokescreens]

Man that’s awesome. Do you know how the internal passages in the muffler are? In quiet mode is it still 3” all the way through?

I asked Corsa if it was 3" everywhere or if i reduced down anywhere. The person i spoke to claimed 3in throughout. I dont have the stones to cut a muffler open to call their bluff.

 

[smokescreens]

Unless my active axleback is worthbsomething to someone i might cut open a stock active muffler to see how its contructed.

 

[WD Pro]

Unless my active axleback is worthbsomething to someone i might cut open a stock active muffler to see how its contructed.

I might save you having to do that

Our euro exhausts get delivered like this :

Which looks a bit shit if your one of those people that doesn't just look at the wheel, but you are tempted to look past the wheel :

So why it was off I took the opportunity to strip it and have it metallic ceramic coated - it should keep it looking good (especially compared to 'as supplied') and it should keep about 30% of the radiated heat away from the diff without having to wrap that area.

Anyhow, the descriptions on how the box works further up this thread are perfect, but I can add a bit more info when you reference these three photos.

Note the spot welds around the box :

They hold an internal baffle plate. splitting the box into two chambers.

I will call the first smaller chamber number 1 and the second larger chamber number 2.

Chamber 1 has a condensation drain.

Here is the non valve outer exhaust pipe internals :

That's the outer box wall you can see (remember our euros have a GPF so the internals are pretty mush as clean as the day they were made).

That pipe is perforated and runs through both chambers, pretty much up to the outer box wall.

Here is the valve inner / central exhaust pipe internals :

Note it was really hard to get a good photo down there as the valve took all the flash and the focus.

By naked eye, you can see straight down it, out of the back of the box and right to the first bend in the exhaust tubing.

Like the outer pipe it's perforated and as best as my eye can make out, I think the pipe has a small gap in it that vents into chamber 1 i.e. rather than one continuous pipe, it looks like two pipes perfectly in line, but slightly separated.

So ...

Valve open = Gas is straight though both chambers with some pipe perforations.

Valve closed = Gas backs up behind the valve. (depending on the box stuffing in chamber 2) a small proportion of the gas will pass through the perforations into chamber 2 and out of the perforations into the other tailpipe. Majority of the gas will pass through the pipe separation into chamber 1, head to the back of the box, to exit the other tailpipe passing some more perforations on the way.

Hope that helps - and saves @skinnyb from taking the sawzall to his exhaust ... lol

WD

WD

 

[engineermike]

It seems like you could see in there from the tip.

 

[engineermike]

Just more info….I bought some stock gt500 and gen2 pieces for various projects and found some interesting things. For one, the gt500 exhaust is all 2 3/4 but it actually necks down to 2 3/8 right at the inlet of the resonator bullets. I think I mentioned before that the flange at the head is a different bolt pattern and the cat is much lower cell count and square matrix (gen3 is hexagonal). The gen2 piping after the cat is smaller than Gen3 (2 1/4” vs gen3 2 1/2”) and Gen2 necks down to 2” at the expansion joint.

 

[GregO]

For one, the gt500 exhaust is all 2 3/4 but it actually necks down to 2 3/8

The gen2 piping after the cat is smaller than Gen3 (2 1/4” vs gen3 2 1/2”) and Gen2 necks down to 2”

I can’t wrap my head around why Ford is reducing sizes at these location. I can understand a size reduction way out back where exhaust gasses have drastically cooled but up front is mystifying.
The GT350 is also reduced as your GT500 description.

 

[engineermike]

@GregO its an interesting subject and it has to do with engineering and fabrication. Raw size isn’t as important as you’d think BUT it takes extra engineering and fabrication method to have low restriction at small sizes. Something like 3” is a good way to ensure you have minimal pressure drop over long distances without having to put much thought into the shape of the flow path. I’m betting that ford carefully engineered these bottle-necks in such a way that they don’t add significant pressure drop at the design flow rate.

In my industry we limit gas flow to 150 feet/s in piping over long distances with minimal engineering, but allow up to 0.9 mach in specific locations where tons of engineering, CFD, and specialty fabrication methods are used.

 

[GregO]

@GregO its an interesting subject and it has to do with engineering and fabrication. Raw size isn’t as important as you’d think BUT it takes extra engineering and fabrication method to have low restriction at small sizes. Something like 3” is a good way to ensure you have minimal pressure drop over long distances without having to put much thought into the shape of the flow path. I’m betting that ford carefully engineered these bottle-necks in such a way that they don’t add significant pressure drop at the design flow rate.

In my industry we limit gas flow to 150 feet/s in piping over long distances with minimal engineering, but allow up to 0.9 mach in specific locations where tons of engineering and specialty fabrication methods are used.

Thanks Mike,
I’ve been able to understand Elston’s header collector “choke” dynamics but don’t know if that applies to full length Catted exhaust systems.
At my friends shop I have seen freakishly small exhaust piping and high HP on newer Porsche turbo vehicles, changing exhaust sizes on those will make something else unhappy.

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