Exhaust restriction since supercharging

[acemastr]

Hi all,

I recently added a roush phase 2 kit to my 2019.
I had issues with misfires and it falling on its face at high rpm which goes away if I open my exhaust valves completely.

Bit of background; my car didn't come with the active exhaust, I bought the mufflers and added a dial polarity switch to be able to open and close at will. This worked great on e85 but if the valve isn't completely open it causes back pressure issues with the supercharger.

My issue is that this thing is so loud now, even with stock cats and an H pipe is unbearable with the valves open.

Can anyone recommend a mild'ish axle back/catback that won't restrict the supercharger? That is confirmed to work with the blower?

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[engineermike]

Are you using oem mufflers or the ones from varex?

 

[acemastr]

Are you using oem mufflers or the ones from varex?

Oem active

 

[engineermike]

I’m still suspicious of your cats. It is possible they’ve disintegrated and are now clogging your mufflers. Your Roush setup shouldn’t misfire due to exhaust. I was running the same basic setup through a single 2.5” exhaust and it still pulled clean. I failed cats and then it started misfiring.

 

[acemastr]

I have spent 35k miles on e85.

That's frustrating. Obviously catless is the best way, but it would make it undrivable for me, so....

Without spending $3000 on kooks catted, do we have a preference?

Appreciate your reply!

 

[engineermike]

The only thing I’ve come up with after years of testing and research is gt500 or hellcat cats. There are 5 sets of gt500 cats on eBay right now but they don’t bolt in.

But before spending more money, log the rear o2 data as previously described to diagnose.

 

[SBR70.3]

I have spent 35k miles on e85.

That's frustrating. Obviously catless is the best way, but it would make it undrivable for me, so....

Without spending $3000 on kooks catted, do we have a preference?

Appreciate your reply!

Texas Speed catted headers.
https://www.texas-speed.com/p-10490-tsp-2015-mustang-50l-gt-headers-and-catted-connection-pipes.aspx

 

[Dsand300]

I’m still suspicious of your cats. It is possible they’ve disintegrated and are now clogging your mufflers. Your Roush setup shouldn’t misfire due to exhaust. I was running the same basic setup through a single 2.5” exhaust and it still pulled clean. I failed cats and then it started misfiring.

I just had the passenger side catalytic convertor replaced (11-19-2024) on my 2018 Mustang GT Premium (with a Dealer installed Roush R2650 supercharger in 2018) with factory active exhaust and a Borla Catback exhaust under the Ford emissions warranty. The vehicle had only 17017 miles. The car started throwing code P0420 at 8500 miles intermitantly after I purchased Mustang used from a Ford dealership in South Dakota in April of 2024.
The code P0420 started coming back on after being cleared every drive cycle at 16000 miles. Eventually the bad catalytic convertor started throwing the dreaded wrench dash icon and would misfire occasionally, going into limp mode. Consulted with my local Ford service shop who recommended a catalytic converter replacment. All good so far. I have read on this forum, that the stock cats don't hold up to the R2650 boost very well!

 

[engineermike]

I’d say the stock cats don’t hold up to any kind of boost very well.

 

[Dsand300]

I’d say the stock cats don’t hold up to any kind of boost very well.

You are correct, engineermike. I haven'y yet had issues with the driver's side catalyst. I have seen in posts, the drivers side usually fails first. The service history of my Mustang GT hasn't indicated the driver'e side catalyst has been replaced under factory emissions warranty.

 

[acemastr]

Pulled the o2 sensor and took a look as best I could. It's intact at least, but is that a blockage in the center?

*Edit* looks like a crack?

 

[engineermike]

Front or rear o2 sensor?

 

[acemastr]

Front or rear o2 sensor?

Front - between manifold and cat

 

[engineermike]

Looks ok for now, what about the other side?

 

[acemastr]

Looks ok for now, what about the other side?

That was drivers side, I had to wait on amazon to deliver my O2 socket. What an absolute nightmare it is under there to do anything.

I'm going to swap the stock non-active mufflers on and see if it helps. Perhaps 'quiet' mode on the active is too restrictive

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