Mustang GT Procharged Potential bad OEM Cat

Nighthawk · Jul 9, 2026

I have 2015 Mustang GT Procharged and have tracked it 8 times. I understand OEM cats can be a problem with Prochargers. I have tracked the car at only about a 6/7 (out of 10) and a few weeks ago finally ran a hot lap in 90 degree weather. The Cylinder Head Temp spiked to 250, I then ran a cool lap and pitted. The check engine light was on it showed some misfires and a P0358 but no P0420 or P0430 codes. My mechanic looked at the Cat and found a few hairline cracks in honeycomb but no melting and we could see through the Cat with a light. I also did a temperature check on the cats, upstream temp was 500 degrees and downstream was 590 degrees. Per AI and another muffler shop the downstream temps (outlet) should be hotter than upstream if the cats are still efficient. Not ready to add headers yet. Should I retire the car from the track or just daily with an occasional hard pull. Any thoughts are appreciated.

stevbd · Jul 11, 2026

I think the misfire is a bigger concern than 7/10ths driving with a supercharger. Misfires on track are really tough on the cats, ask me how I know. But of course, it can be hard to have the self control to stay at 7/10 and as you start to push harder you will have more issues with cooling no doubt.

Junkyard Dog · Jul 11, 2026

It's only money.

The cats can be replaced with cats meant for the kind of horsepower you are pushing. They are expensive. I am not talking about marketing "high flow" nonsense. Get cats rated for the actual horsepower. Your cats are rated for about 215 horsepower per side. <--- I mean, really, why would you expect them to live in your pro charged car?

Then you need to cool off the car on track with a procharger. The stock cooling system was designed to shed the heat from a 435 horsepower engine when driven to the grocery store. It was not even designed to cool that engine off on a racetrack. Once you added the prochargers, you have overtaxed the cooling system. Better oil cooler, better radiator, ducting, ventilate the hood . . . . but none of that will help the stock catalytic converters survive all the extra horsepower you are pushing through them.

Nighthawk · Jul 16, 2026

Hey Junkyard Dog thanks for the insights. Yeah I've been looking at some Stainless Works High Flow Cats with metallic substrate. Also to your point about the heat I was at track just yesterday, it was hot in Atlanta and a friend ran his GT350. He lasted 4 laps before heat became an issue, Cylinder Heat Temps were 250 degrees but oil timperature was 300 degrees.

Nighthawk · Jul 16, 2026

stevbd said:
I think the misfire is a bigger concern than 7/10ths driving with a supercharger. Misfires on track are really tough on the cats, ask me how I know. But of course, it can be hard to have the self control to stay at 7/10 and as you start to push harder you will have more issues with cooling no doubt.

Hey Boss,

Thanks for the insights. I did bring it to a couple mechanics and one said that's the firsty place to start diagnose the cause of misfires. I also got compression and cats checked and they are both good for now. Like others have mentioned oem cats and Prochargers aren't a good match. The issue occurred 2 weeks ago when I was tracking with Porsche Club America. I passed a few slower porsches but got tired of getting passed by the faster ones. I tried to catch some of the faster ones, didn't pass them but it was fun chasing them until the check engine light came on.

Junkyard Dog · Jul 16, 2026

Nighthawk said:
Hey Junkyard Dog thanks for the insights. Yeah I've been looking at some Stainless Works High Flow Cats with metallic substrate. Also to your point about the heat I was at track just yesterday, it was hot in Atlanta and a friend ran his GT350. He lasted 4 laps before heat became an issue, Cylinder Heat Temps were 250 degrees but oil timperature was 300 degrees.

Atlanta Motorsports Park or Road Atlanta?

Nighthawk · Jul 17, 2026

Junkyard Dog said:
Atlanta Motorsports Park or Road Atlanta?

Road Atlanta.

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Mustang GT Procharged Potential bad OEM Cat

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