1996 Toyota Corolla exhaust Manifold Cracking

Hello; Can someone tell me why my 96' toyota corolla which has had four exhaust manifolds replaced during 50,000 miles of operation continues to crack the exhaust manifold? The manifolds I have installed are all after market, made by different manufactures, supposedly made to higher standards than the original to aviod cracking problems. The new manifolds were all installed with all new gaskets and the manifold bolts were all torqued to toyota specs. I have heard that these corollas are known for having this type of problem, but this is absurd.The car has 160,000 miles and runs great except for this continuing problem. Any Suggestions?

Thank You

 

You could have a missing or failing engine mount
With the placement of the engine/manifold on these cars such a failure could lead to undue stress on the manifold

It's also doubtful the A/M manifolds are actually made to better standards then Toyota
I wouldn't say that about everything automotive, but in this specific case I have to say it's highly unlikely....more likely the "better quality" is a marketing depts. dream or an incorrect consumer assumption or rumor (myth)

I'd consider using a Toyota replacement part if you fix the (other) problem (causing the breakage)