No difference. Seems mainly down to RPMs and load after coming from both and removing load from the engine with clutch in, whether maintained or shifted to neutral and clutch released.

So are your problems fixed with the clutch change?

How much power are you putting down, how many miles on the clutch and what type of activity has the clutch seen (highway, street, track, mixed)?...just good reference info for anyone shopping for clutches.

Unless the leak is coming from the header itself, before the primary o2 sensor, no - it shouldn't affect how the car runs in any tangible way. It would just affect how the car sounds/smells.

If you have a leak before the primary o2, that can cause all kinds of problems - but that seems incredibly unlikely unless you have an aftermarket header and a weld has failed.

I have had cars develop cracks in their OEM manifold. It is usually at the weld like you mentioned. Usually manufactures will use mild steel for the welds, even on stainless steel headers, and I think our headers are mild steel, so they are rust buckets just waiting to crack with higher miles.

If his profile is right, he has the P-Tuning header. So all bets are off :D

Isn't the chances of cracking even higher with aftermarket headers? I feel like they use thinner gauge tubes, but Ptuning probably is better quality than most of the headers out in the world.

Edit: that and manufacturing tolerances can be much poorer.

If they're built right they won't crack. Aftermarket headers always crack in the welds if they do. It's usually due to one of the welds not being properly inspected and they miss a fisheye, from where a crack can grow. The base material is more than strong enough even with the thinner walls.

Sorry if I was being confusing by discussing thin gauge metal, maybe sounding like I was implying the cracks would happen mid pipe. I meant still at the weld. Thinner pipes mean weaker joints at the welds. Welds are just the weakest part of the system.

It's the heat affected zone surrounding a weld and poor fatigue detailing that usually cause problems. Bad welds can pass a visual inspection.

While that's true, on every header I've personally seen crack it originated from a fisheye in the middle of the weld.

I don't see the contradiction since that's ultimately a poor fatigue detail/bad weld passing inspection. A weld with a fish eye will last for a time. Also, my post was meant as an elaboration on "Thinner pipes mean weaker joints at the welds. Welds are just the weakest part of the system." Welds are generally not the weakest part of the system unless the welding is sub-standard, though I reckon that's a fair assumption in some segments of the automotive aftermarket.

The pipe to weld junction is the weakest part of the header. This really isn't saying anything that shouldn't be pretty obvious. The welds themselves are usually stronger/thicker than the pipe but much more brittle. The pipe is flexible and decently strong. The flanges are thick and strong. The unions of pipes to flanges, which are the welds, are obviously the weak link. Moreover, the thinner the gauge metal, the weaker this junction will be. Why?

Thinner metals of the same quality will deform more to heat, which will put stress on the header, most critically at the weakest link in the chain. Also, thinner metals are inherently weaker to vibrations and compression/tension forces. This can be problematic for headers that are poorly designed to deal with loads like the weight of a turbo or exhaust system, or for headers that lack support braces, or those that have quality control problems for fitment/alignment issues.

Fisheyed welds seem to exist in thinner gauges where the welder did a stream of spot welds with lift before saturating the surface, perhaps moving quickly to avoid blow through. That happens at the last weld too when lifting before saturation. These welds are at risk of failure along the weld like you said, but again, they would correlate higher with thinner gauged metal (I'm saying from an educated guess)

If you look up cracked headers, you will find all types of cracks, but a reoccurring crack will be a seam running parallel to the edge of a weld. This is likely due to the joint where a flexible pipe meets a stiff and brittle weld and/or junction. Just like how most muscle tears occur at the muscle tendon junction, this is the weak link where the weld is at its thinnest, where the pipe may have thinned during the welding process, and where the forces of flex meet an inflexible point along the header.

To answer questions:

PTuning Header
JDL Front/Overpipe (Vband clamp at front and over sections)

The exhaust sounds are definitely coming from the front passenger side of the car and I've already checked both the vbands for the header and the JDL F/O Pipe.

I still have my stock header, but I'm hesitant to put it on when my tune was optimized for e85 and the header. I used the Grimspeed mls gaskets for both the head to header and header to f/o pipe, but it wouldn't surprise me if somehow a weld failed or the header flange isn't sealing to the head.|

Edit: If the Header has failed, I guess the next question is what are our options? I can pass emissions in my current residence with the cat in the front pipe.

You mean you checked and you couldn’t find the leak? Use a feather or something light to find the air, or spray mist over the pipe, or spray soapy water on the pipe directly.

If it is the flange then try a different gasket. If it is a crack then get it welded.