Hey all, i'm going to have this dillemma coming up soon. I'm gonna score a set of big outlet manifolds to replace the TBI manifolds my 92 LB9 A4 has. I'm gonna hog them out as best i can .
The question then becomes, what shall i run from there. I may be getting a stock y pipe w/ 3" cat with 'em, but stock Y-pipes are pretty ugly more like a T. I'd really rather run an aftermarket Y, i'm assuming they have actually thought it out and made the junction smooth like header y-pipes. Thing is, all the aftermarket Ys i have seen are 2.5" which seems like overkill for my 305.
Then i was thinking, a dual cat set-up would be more 'correct' on my car anyway. I'm assuming i could still get the head pipes i need form the dealer, add my own high flow cats and an aftermarket cat back with a nice Y.
Cost isn't a huge factor, obviously, the dual cat option would cost the most as i would have to buy 2 high flow cats as well as the head pipes. I can't help but think that the dual 2.25" head pipes would be a better set-up than 2.5" pipes though for overall performance.
I need to decide all of this before i put any of it on since i will need a different cat back depending on if i go 3" single or dual cat. If i decided to stay 3" single i could actually even hold off on the aftermarket y for now, which would be a big help in getting this on ASAP.

...so, what would you do (or have you done?)
...ed

 

bttt, c'mon somebody must have an opinion, or is the exhaust board just about pointless debates like which high flow cat is worth an extra half HP, and 'dude, my fromaster sounds great'
...ed

 

Well High school geometry can answer this question.two 2 1/2" cats will flow roughly the same as one 4". Since a 4" cat is quite a pretty penny i would stick with two High flow 2 1/2"s Walker/dynomax makes them for about $40-$50 a peice.

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1991 Z28 500hp383 TCI 700R4

 

And grade school reading comprehension would tell you that i asked about the suitability of the dual 2.25" cats as came stock on later f-bodies w/N10 that have a nice smooth Y after the cats vs. an aftermarket 2.5" Y-pipe that feeds a single 3" cat.
The latter is the cheaper set-up, but for a car that i'm working on as a sleeper that is only destined to perhaps make 300hp, dual 2.5" primaries on the Y seem like flow killing overkill. I was looking for experiences of people running the 2.5" aftermarket Ys to see if they performed well on relatively stock cars.
And if you wish to respond that how could a 2.5" y-pipe not flow better than the 2.25" dual cat set-up, i will refer you to high school physics, the chapters on fluid dynamics.
...ed

 

Ed, don't have any experience with the aftermarket 2.5" Y setup but can offer some data on N10 that might be helpful. From the dealer, this assembly includes the head pipes, both cats, and cat exit pipe(s) that hook up to the cat back. So if you want to run aftermarket cats, you'd have to cut the stock ones out and reweld your new ones. It's also an expensive piece. I had my N10 setup replaced under warranty and the list price was $975. If it still runs that much it'd be tough to justify based on cost. Think it'd work well with your setup though.

 

**** you then retard, figure it out on your own

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1991 Z28 500hp383 TCI 700R4

 

HOLY ****!!!! $975...yeah, i think i'll pass on the N10 then unless i can score a used one cheap in the meantime. Else i'll just use the stock 3" single cat Y until i really need a bigger Y.
...ed

 

there's a duel cat setup on e-bay right now ~$104.00

Item #565006121

I've never tried the embedded HTML and im not gonna try now but here you go:

http://cgi.ebay.com/ebaymotors/aw-cg...006121&r=0&t=0


James