Factory Exhaust Manifold horsepower data

[tgonyaw]

I found an advertisement from Lingenfelter showing the 368 ci LT-5 at 530 hp. Is that number before the factory exhaust manifolds and cats are installed? The add has an EPA number for this configuration. How much horsepower do the stock exhaust manifolds with cats support?

Thanks for any opinions and insights.

http://lingenfelter.managecontent.co...hp-368-cid-lt5