I was going to delete the primary cats and make a new front section of the exhaust but hard-to-find flanges and effort to weld the bungs, bends and mounts is making me have second thoughts.
What do you guys thing the leanest safe AFR at redline is that's safe not to damage the stock primary cats that are very close to the exhaust manifolds?
I would normally run it at about 0.87 lambda or 12.8:1 if only the secondary cats are in place but this is probably a bit hot for the primary cats.