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Exhaust Pressure Testing

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engineermike

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Will you retest your exhaust back pressure test after installing the Jones mid-muffler ?
No, being 3” straight through I’m betting it hasn’t changed.
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K4fxd

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Have you dyno tested or track tested the Jones muffler? I'm seriously thinking about sending mine back due to the crap internal construction and the wide open turbulence chamber. I don't think that spot weld will last over a year. I afraid it will start rattling and cause false knock

1698754887141.jpeg
 

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Have you dyno tested or track tested the Jones muffler? I'm seriously thinking about sending mine back due to the crap internal construction and the wide open turbulence chamber. I don't think that spot weld will last over a year. I afraid it will start rattling and cause false knock

1698754887141.jpeg
It's one data point but the fastest and quickest person I'm aware of with ESS' smallest blower (G2 with 100mm pulley running 9.4x @ 149.xx) runs this resonator and has been doing so for over a year.
@kevinvan6000
 

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It's one data point but the fastest and quickest person I'm aware of with ESS' smallest blower (G2 with 100mm pulley running 9.4x @ 149.xx) runs this resonator and has been doing so for over a year.
@kevinvan6000

Yeah I think even if it was a small restriction it would be so minimal it wouldn't be much of a concern. I understand being efficient and looking for every last hp but as I tested plus or minus another 5 or 10 hp or so at 800 hp you're not going to notice. The weight savings if any you'd probably notice more at the track.

Having your shift schedule optimized will provide much more gain then any different exhaust combo. Many times the shift schedule is not though. I'm just saying I think sometimes people can get too caught up in exhaust looking for just a few extra hp.
 

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28 pages in

Cliffnotes on the experiment??
 

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engineermike

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Wut he said

- Bigger is better. 2.5" really isn't big enough for a SC Coyote.
- Stock cats aren't that bad for restriction, but they are bad for longevity.
- There are few true dual straight through 3" resonators.
- StainlessBros, but the walls are paper thin and they fail.
- Jones has an H-pipe built-in but some earlier versions necked down to 2.5" internally.
- Oddly, I learned on the dyno that you actually can go too low on backpressure. Once my entire system was full 3" straight through, adding cats back in actually gained about 15 hp, to everyone's surprise. It is possible that some more work with lambda and cal timing could get it back but still.

@K4fxd tge jones is on my buddy’s car and it’s doing fine. I think I got a sb with thicker walls because mine is still hangin in there.
 

K4fxd

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Oddly, I learned on the dyno that you actually can go too low on backpressure. Once my entire system was full 3" straight through, adding cats back in actually gained about 15 hp, to everyone's surprise. It is possible that some more work with lambda and cal timing could get it back but still.
That is a bit of a surprise. I suppose more tuning would get the 15 plus more. If back pressure was needed every race car would have some.

I think there is a reflected wave from your cats causing a bit of ram tuning from the exhaust. Just my EWAG (Educated Wild Ass Guess)
 

K4fxd

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tge jones is on my buddy’s car and it’s doing fine.
Good to hear. I think I'll install the one I have, I'm ready to quiet the car down some.
 

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engineermike

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That is a bit of a surprise. I suppose more tuning would get the 15 plus more. If back pressure was needed every race car would have some.

I think there is a reflected wave from your cats causing a bit of ram tuning from the exhaust. Just my EWAG (Educated Wild Ass Guess)
Keep in mind we have a ton of valve skirt area which allows a lot of low lift flow, and the tivct means we’re running a lot more overlap at wot than a typical street street or sc cam would. Then add boost to the equation. The stock exhaust imposed 10-15 psi backpressure so blowthrough would be reduced a lot. The Roush stock cal even accounts for charge blowthrough to correct the o2 sensor reading, so we know some bypassing is happening. My guess is that significantly reducing overlap up top is what it would need if your backpressure is Uber-low. However, every aftermarket tune I’ve laid eyes on runs the same overlap regardless of exhaust. Roush runs a lot more.
 

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Keep in mind we have a ton of valve skirt area which allows a lot of low lift flow, and the tivct means we’re running a lot more overlap at wot than a typical street street or sc cam would. Then add boost to the equation. The stock exhaust imposed 10-15 psi backpressure so blowthrough would be reduced a lot. The Roush stock cal even accounts for charge blowthrough to correct the o2 sensor reading, so we know some bypassing is happening. My guess is that significantly reducing overlap up top is what it would need if your backpressure is Uber-low. However, every aftermarket tune I’ve laid eyes on runs the same overlap regardless of exhaust. Roush runs a lot more.
Just a thought, any possibility the catalytic monolith cores are contributing by creating a more laminar exhaust flow post catalytic vs systems with no catalytic.
 
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engineermike

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One of my favorite dyno days. All true 93 octane with no booster, meth, or eth.

Light blue is 3.875 pulley, no cats, and 20-21 deg timing. Some argued that on pump gas you be more knock limited so larger pulley and more timing would make more power. They were wrong.

Gray was 3.5 pulley and iirc 17-18 deg timing. No cats.

Then we installed cats while still on the dyno and made one last pull, the dark blue line.

image.png
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