Smells like exhaust in the car

So from this forum I read it could be taildraft.
I have a OXB-R header,AEM CAI, and Greedy Exhaust with the cat gutted. Could the header leaking fumes that the CAI sucks in? Could the Cat be leaking up into the car?
Any ideas? What can it be and how can I pinpoint the problem?

i have this same problem when ever i push the car really hard. for a while my stock header was leaking so i replaced it with aftermarket and the gasket and its not leaking anymore but i still smell it.

I dont really know hwo u can pinpoint it but i remember when i used Seafoam in my brakebooster letting it pour in slowly as it smokes up i can see leak from header and i was like wtf and so i look under car and saw smoke coming from cat area too so maybe u doing that help clean engine and have better idling yet pinpoint it? ITS just a thought/idea