How many convertor on 07 Chevy trailblazer?

It depends on what engine you have. I'm seeing one catalytic converter for the 4.2L V6 and one catalytic converter assembly, containing two converters, for both V8 engines. It's important to know if you have California Emissions. If the emissions decal under the hood says C.A.R.B. compliant, you have California Emissions. Hope that helps! Jim

I've seen 2 converters on a 4.2 liter trailblazer

Where's the second one, Jeff? It's not part of the exhaust manifold, I checked. Am I missing something? Jim

There's only 1 cat on the inline 6 4.2. Being it's an inline 6 and not a V6, the cat comes off the 1 the exhaust manifold on passenger side. There's only 1 there.