430 Surprising new exhaust note

What muffler mounts do you have installed? I would start by looking at those. Your stock manifolds would be the second item to look at. Even the newest iteration were prone to cracks.

 

I went with the Tubi headers. No CEL, sound slightly louder and deeper than stock, and have heat shielding as part of the design. Plus, they look good.
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I would still check the exhaust brackets and do a thorough check of your muffler section and exit tubes from underneath to see if you developed a split.

Long story short, I was using the wrong brackers with my aftermarket exhaust. One of them eventually failed and caused a healthy split on the underside of one of the tubes that sounds exactly like you describe, except for hearing a metal bang.

This year I'm going with Valvetronic Designs catless manifolds and whatever 360Trev recommends as the best way to flash out the CEL they will cause. As long as the manifolds are equal length (I have an inquiry in to verify). They are a 4-2-1 design which preserves the OEM-like exhaust pulses and engine note of the original manifolds.

 

I would read out the ECU. I would then check the entire exhaust system, including the catalytic converters. The inner monoliths can become loose here or can shaking inside. Manifolds crack in every generation, but you can't see this from the outside. You can usually smell it and hear it if you stick your head into the engine compartment near the manifold. You can be absolutely sure after removal.

I think you have the Capristo Racing, which is designed for the high sound. The Capristo manifolds are the best for performance. If you want an even higher sound and a manifold that is on a par with the Scuderia or Challenge manifolds in terms of performance, then I recommend the Kline. These are the only 4 in 1 manifolds that the car can handle and do not lose power without a tune and they have a high pitch.

What I wouldn't completely rule out would be both or a crankshaft position sensor. If the valve overlaps no longer fit 100%, then it sounds much deeper, but also no longer has full power. I've already had this with two vehicles. Everything else was fine and I couldn't explain why it suddenly sounded so deep, even though a Kline was installed. I was then able to turn the car off and on again and the high-pitched sound was back. Only when an error was also in the ECU (but without an engine control light) did it no longer help to switch the car off or on again. Then we had to replace the sensor and everything was fine again.

What somehow still doesn't fit 100% is the bang as if from a door, at most a violent stress crack of a part. But it's very difficult to judge this in front of the laptop and not on the car.

 

I bet it’s your headers. I’d be swapping for aftermarket. I’m pleased with my Capristo set up.

 

How much were these and what year is your car??

 

Michael, I paid around $5400 delivered. My car is a very late 08 model. The original manifolds were replaced at about 10K miles for cracks, although I smoke checked the stock manifolds when I replaced them and they had no cracks. I installed the Capristo exhaust brackets shortly after taking delivery, which I think helps, although I acknowledge you can remove the lower brackets and achieve the same result.

 

I have the Challenge headers and they are a bit louder than stock because they lack the pre-catalytic converters. I got them when they were much cheaper, they are about double now and if I had to pay what they cost today, I would buy the Tubi.

 

Thanks for posting what the problem was. As for the challenge headers, there are many here running those and are very happy with them. They use to be much cheaper so it was the preferred "fix" for the header issue. As they've gone up in price, the aftermarket options start to play in.

I'm wondering if the sound you heard was the seal breaking between the exhaust manifold and the head itself. Perhaps the bolts had worked loose but the seal was holding until that last initial start broke it free.