MustGoFastR said:
Interesting. Can you post pics here? The '35 has four cats as well, but they are incorporated into the down tube that goes between the exhaust manifold and the Y-pipe; we can just replace that section with any of the single, high flow aftermarket offerings.
It has been determined that our engines are very nearly clean enough to run with no cats whatsoever, so going to a single high flow unit is not a problem as far as emissions testing is concerned. I'd wager the 4.5 is in the same boat, so perhaps you could just swap the pipe the lower pipe/cat out with a straight pipe? You'd retain the upper cats and eliminate the lower ones; should help some. The other alternative is to have high flow cat replacements for the lower pipe/cats and gut the upper cats (don't ave to worry about ever replacing them, then.). This would give maximum results.
I swear when I changed the oil last time, this was how the cat setup for my 45 was, too. Dual cats on the downpipe; I didn't see any pre-cats on the manifold itself.
I remember reading about the stock cats burning up (melting, actually) on some of the other cars that share the Fm paltform. (350z, G series). Does anyone know which cat burned up? The front ones, or the rear ones?
I know the Sentra Se and SE-R models were having melting cat issues due to their close proximity to the exhaust ports.
When I was under the car, I remember noting how close in proximity each bank's cat-cons were to each other. Seemed like a poor design to me. First you have the pre-cat so close to the exhaust ports (I know it's 'needed' due to EPA), then not even a foot downstream, the other cat is right there.
Since the exhaust gets hotter after the first cat-con, the temps have to be ridiculous for the 2nd cat-con. My guess is that this one could melt.
Most of the newer cars w/ the cat-cons located so close to the engine have to run really rich under WOT, so not to burn the cat-con. Kinda sucks for performance.
I can't remember where the last O2 sensor is plumbed in, but if it's after the last cat-con, I may just cut out the pre-cat, slap on a SAFC-II and lean out the WOT settings to pick up some HP.