2008XBlimited

i was looking over my engine bay this weekend and noticed the stock exhaust seems to be a 4-1 header setup. honestly, was shocked to see this on a stock setup.

question, whats with it?

06tcdude

It is a 4-1. 1 big a$$ catalytic converter. Followed by another catalytic converter, then a resonator.

FromTheOld

It's a 4-1 header made of 409 stainless steel that has some crush bends in it that leads into a primary catalytic converter. What else is there to say about it?

buickid

Its made of metal.
/thread

TrevorS

iTrader: (1)

I understand it's referred to as a pre-cat. Purpose being to get an early start on emissions control while the main cat heats up to the point where it starts to do its job (cold catalyst doesn't accomplish much). The small pre-cat at the manifold heats much more quickly than the big main cat that comes later.

However, I don't think the pre-cat makes much difference after the system achieves normal operating temperatures, and so I'm curious to learn what emissions inspections in states-that-care come up with when the pre-cat is absent.

streetxdreamer

Im not really sure what you question is asking. Are you reffering to 4-1 as in you thought that aftermarket was the only way to get 4-1 Headers?

FromTheOld

Eh, I worded it differently but its the same thing. I consider it the primary cat cause:

#1. It's first.
#2. There is a sensor that senses if it is gone or not, which may or may not say something about it's importance.

Pre-cat, primary cat, either way, it's a catalytic converter.

Zsanz

anybody gutted the cat on the header?

CIONIDE

iTrader: (1)

They will fail you on your smog test in Cali, which means no renewal of your vehicle registration. It doesn't matter if your exhaust emissions would have been in the passing range, they do the visual inspection first, and it's an automatic fail if you don't have the correct number of factory specified cats.

Also, if Johnny Law spots it, you can receive a citation for modified exhaust system. This usually only happens when there is a crack-down at a meet that is disturbing the peace, or the individual is being obnoxious to Johnny.

TrevorS

iTrader: (1)

I wasn't meaning to correct you, just to clarify. The pre-cat has a perhaps important purpose, but in terms of overall impact on emissions, the center cat would generally be thought of as being the "primary" contributer. Just don't want people to get the wrong idea !

Yikes! OK, so, as usual, CA is very hard nosed about it. I wonder what the story is in other states-that-care. Do they all count the cats, or do some (or most) just go by the emissions numbers? I know my state, DE, does an under car visual for the main cat and also checks the numbers. I've no idea if it also checks for pre-cats.

ScionFred

iTrader: (1)

IMO doing so would lose power. The pre-cat is a pretty high flowing metallic substrate cat so it isn't terribly restrictive. The problem with gutting it is the large diameter of the empty canister and the effect it would have on exhaust gas velocity and scavenging. I've seen comparisons between gutted cats vs test pipes and IIRC the test pipe made more power every time.

IMHO the biggest restriction in our exhaust system is the tiny 1.8" ID pipe between the scuba and the axle-back. I was shocked when I measured it and discovered how small it really is. 2.25" ID should work very well for a N/A XB with the typical IHE mods.

FromTheOld

Most catalytic converters aren't a huge restriction, ESPECIALLY in N/A cars. It's mainly the tubing diameter, and the type of bends involved (crush bends are bad. turbulent and restrictive). Baffled mufflers are pretty restrictive too, but sometimes they're required to keep a nice sound that won't annoy people

LtBradleykins

So here is probably a stupid question, but I take it that N/A means non Aspirated? As in Fuel injected not carbs? (not the bready kind either ;) )

CIONIDE

iTrader: (1)

Actually it stands for Naturally-Aspirated, as in not force-fed (Forced Induction) by a turbocharger or supercharger.

LtBradleykins

Ahh... I see! Well thank you! Still learning all the acronyms to things. lol

CIONIDE

iTrader: (1)

No problem, that's one of the reasons these forums are here.

You don't learn if you don't ask questions.

TrevorS

iTrader: (1)

The one that tends to get me is F/I. It stands for Forced Induction, but my off-the-cuff interpretation tends to be Fuel Injection ! I often have to catch myself on that one.