Exhaust Pressure Testing

[engineermike]

Nice work @engineermike ! Any plans to change hardware based on data?

Man I’ve been contemplating that myself. The problem is the pressure drop is fairly evenly split between the cats, 2.5” piping, and resonator. There’s no single bottleneck that will address most of the backpressure. (I suppose I do need to verify the 3” resonator-back imposes nearly 0.) I hate it that no one seems to offer a true dual 3” resonator.

This data seems to indicate that a supercharged coyote really needs dual 3” all the way to the cats. I think backpressure can be reduced to the 5-7 psi range if done that way.

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[80FoxCoupe]

Man I’ve been contemplating that myself. The problem is the pressure drop is fairly evenly split between the cats, 2.5” piping, and resonator. There’s no single bottleneck that will address most of the backpressure. (I suppose I do need to verify the 3” resonator-back imposes nearly 0.) I hate it that no one seems to offer a true dual 3” resonator.

This data seems to indicate that a supercharged coyote really needs dual 3” all the way to the cats. I think backpressure can be reduced to the 5-7 psi range if done that way.

When you say 3in for supercharged coyote, must elaborate a bot more. 700hp or 1200hp? The requirements would of course be different.

 

[engineermike]

When you say 3in for supercharged coyote, must elaborate a bot more. 700hp or 1200hp? The requirements would of course be different.

Well I’m just running a stage 2 Whipple on a 3.625 pulley and the 2.5” sections are adding what I would call excessive backpressure. All the PD kits out there are set up to push more air than the Whipple so I’d say theyare roughly equivalent to mine in airflow. Not sure about the centrifugals…

 

[80FoxCoupe]

Well I’m just running a stage 2 Whipple on a 3.625 pulley and the 2.5” sections are adding what I would call excessive backpressure. All the PD kits out there are set up to push more air than the Whipple so I’d say theyare roughly equivalent to mine in airflow. Not sure about the centrifugals…

Well I’m just running a stage 2 Whipple on a 3.625 pulley and the 2.5” sections are adding what I would call excessive backpressure. All the PD kits out there are set up to push more air than the Whipple so I’d say theyare roughly equivalent to mine in airflow. Not sure about the centrifugals…

I can see there being pressure differences across the rev range with different types of forced induction at the same peak power range. But in theory at peak power the back pressure would be the same across the kits for a given horsepower. It would be interesting to see how a PD kit and centri kit would stack up both at 700 wheel horsepower.

 

[kevinvan6000]

Man I’ve been contemplating that myself. The problem is the pressure drop is fairly evenly split between the cats, 2.5” piping, and resonator. There’s no single bottleneck that will address most of the backpressure. (I suppose I do need to verify the 3” resonator-back imposes nearly 0.) I hate it that no one seems to offer a true dual 3” resonator.

This data seems to indicate that a supercharged coyote really needs dual 3” all the way to the cats. I think backpressure can be reduced to the 5-7 psi range if done that way.

Would something like this work for you? Its 3" with an internal x-pipe but it maintains the 3" diameter all the way through. I run one on my car.

https://www.summitracing.com/parts/jex-mf2469/overview - note the pic Summit uses is a generic picture, it actually looks like this:

https://www.summitracing.com/parts/jex-mf2468?rrec=true

 

[Andrew@Lethal]

I recently did some exhaust pressure testing and thought I would share my results for anyone interested. I've done exhaust pressure testing before and found power by relieving it. For reference, Lingenfelter IIRC once wrote that exhaust pressure should be kept under about 5 psi, but turbo setups can run over 50 psi.

The setup is a Stage 2 Whipple 2018 Mustang A10, running 93 octane, the XDI HPFP, and the 3.625" pulley for about 13 psi boost. The exhaust pressure rises with rpm, so the below numbers were recorded at peak pressure at the shift point, or about 7400 rpm.

Full stock exhaust measured 15 psi ahead of both cats. One cat is fairly new with about 5k miles, while the other is original with about 33k miles, but they both measured the same. My assumption was that most of the pressure was being imposed by the cats so I moved downstream of the cats and, to my surprise, measured 13 psi.

Next, I swapped to a Magnaflow Street series cat-back (model 19370). I measured 11 psi ahead of the cats, for a reduction of about 4 psi. Downstream of the cats measured about 6 psi, so the cat-back successfully knocked 7 psi off of the after-cat number.

On one hand, the Magnaflow reduced the after-cat pressure quite a bit from 13 psi to 6. On the other hand, I honestly expected it to be lower with the dual 3" system with straight-through mufflers.

Another oddity you might notice is that the cat dP went from 2 psi to 5 psi. The cats, of course, didn't suddenly become more restrictive. What likely happened was that the cat-back reduced the pressure at the cats, which in turn increased the volumetric flow rate of the exhaust and, thus, the velocity through the cats. With higher velocity comes higher pressure drop.

Next, I am wondering how much the 2.25" factory-connection is hurting it. It's 2.5" upstream and downstream of this connection and it's obviously the smallest diameter in the system.

On a final note, with a knock-limited supercharged Coyote, spark timing is the key to making power. The reduction in exhaust pressure of 4 psi should allow about 1 deg of additional spark timing according to the link below and professional contacts, which in turn would make about 20 more hp due to timing alone.

https://etd.ohiolink.edu/apexprod/r...ssion=dayton1375262182&disposition=attachment

Awesome work!

 

[engineermike]

@kevinvan6000 i looked at that one and it appears to neck down internally:

 

[engineermike]

Awesome work!

Thanks! The Whipple and magnaflow both came from Lethal.

 

[Andrew@Lethal]

Thanks! The Whipple and magnaflow both came from Lethal.

We appreciate your business! #Teamlethal

 

[engineermike]

…It would be interesting to see how a PD kit and centri kit would stack up both at 700 wheel horsepower.

Since power and mass air flow are very closely related, my guess is the numbers would be very close. E85 cars running 23 deg timing and less boost to achieve the same number would probably have less, as would turbo cars (after the snail). I bet the centrif cars have less backpressure in the midrange though.

 

[GT 550]

Great work on the data!

Is this the section that was 2.25", now 2.5"? Curious about why it's necked down in the middle noting that even going from 2.25" to 2.5" made a difference?

 

[GregO]

I hate it that no one seems to offer a true dual 3” resonator.

https://www.stainlessbros.com/3-dualdual-ss304-thin-oval-muffler-17-oal--polished.html

Might not exactly match the S550 110mm exh. Center to Center dimension but at this point any Fab guy worth their salt can make this new Stainless Bros. dual in/out fit.

 

[engineermike]

Is this the section that was 2.25", now 2.5"?

Yes

Curious about why it's necked down in the middle noting that even going from 2.25" to 2.5" made a difference?

Stock, the pipes from the cats to the stock band-clamps are 2.5". For reasons only Ford knows, it necks down to 2.25" where the band clamps are and stays 2.25" through the stock resonator, then necks back up to 2.5" just after it and stays that way to the mufflers. Nearly all the aftermarket cat backs neck down to 2.25" to connect with the factory band-clamp for ease of installation, and I'm sure it works just fine at 500 hp. I'm learning that dual 2.5" isn't big enough for the 800+ hp range.

That said, it's quite clear Ford put a lot of effort into engineering a sound for the Mustang. It's really hard to beat the sound tone of a stock gen3. It reminds me very much of a fox body 5.0 with 3-chamber Flowmasters back in the day.

 

[engineermike]

https://www.stainlessbros.com/3-dualdual-ss304-thin-oval-muffler-17-oal--polished.html

Might not exactly match the S550 110mm exh. Center to Center dimension but at this point any Fab guy worth their salt can make this new Stainless Bros. dual in/out fit.

Are you certain it's 3" all the way through? Every one I've seen so far necks down either just inside or just outside of the casing, including FlowMonster, Borla, and Magnaflow.

As far as fitment goes, if I do anything with this, it's going to involve going 3" all the way to the cats which will require quite a bit of fitting anyway, so the center-center won't matter much.

 

[GregO]

Are you certain it's 3" all the way through? Every one I've seen so far necks down either just inside or just outside of the casing,

I think Stainless Bros. recently added this dual in/out to their product line.
Knowing Stainless Bros. I’ll wager it’s 2.875” ID (3.0” OD) perforated tube.
These guys build and supply top notch parts.

Here’s their 3.0” bottle resonator end connection. I’d don’t see why they wouldn’t use the same connection style on the dual in/out.

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