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2.5" vs. 3" cat or Y back exhaust?

20263 Views 30 Replies 11 Participants Last post by  Strategy9
In a previous post I asked about quiet performance mufflers and pretty much narrowed it down to Dynomax super turbo or Walker quiet flowSS in a large size can, single outlet. My exhaust guy says he'll do either 3" or 2.5" tailpipe w/muffler for $170 but if I want him to wack off the end of the Y and put on a better 2" to 3" collector then do 3" all the way it'd run about $250. Both sound pretty reasonable to me, here's the question for an '04 4.7L 4x4 DAk QC:

With only mods planned being a set of HO cams and moddified TB plumbing to modded air filter box lid(larger) & an sct tune is there really anything to be gained or lost by going to 3" ex. pipe all the way with my few mods? Bottom to midrange is what I would hope to increase. My impression from searching is the general concensus is that the 4.7L engine likes 3" plumbing, is this in all cases, regardless of mods or lack of? Thanks, Mark
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More info on a 2.5 to 3" y pipe. Our trucks only have 2" before the Y. A Y pipe from a Ram will fit our trucks? What year Ram? What about the cats?
People use the step ups to make it work on our stock Y pipe. I think I might end up doing this for my truck, I just bought exhaust for my car that came with a 3" cutout welded in that I'm taking out (Borla adjustable, it has a spot for the cutout on it already not sure why they welded one in) and putting on my truck. I figure I already have the cutout, all I need to do is buy the 2.5-3" Y and cut a chunk of pipe out before the 3rd cat (or cut it out completely, but that would make the cutout all but pointless as I have a CB Extreme muffler). For the whole size thing, I would say go for 3" as it isn't going to be mandrel bend 3".
I would just replace it with the 2x 2.5 to 3" y-pipe(just the Y, not the whole manifold to Y). Everyone says that is the worst part of the exhaust, making a wider opening after that isn't going to help a whole hell of a lot and they are only like $30 for the y-pipe, say $60 total to get two adaptors welded on so it will work with the stock y-pipe
Anyone have a picture of the stock Dakota Y for him? I just cut out my 3rd cat this weekend and couldn't believe how small the holes were, like little 1 1/2" pipes being merged it looked like. I didn't get a chance to take a picture, but jesus does that thing have to restrict a lot of flow.
For sure, the openings in the stock one are EXTREMELY small! Made me pretty mad that I didn't have one when I was cutting out my 3rd cat, but I'm pretty sure that was clogged up and needed to be done right away. I think the best thing to do if you want to keep it cheap is by doing what I have planned: Get the 2.5-3" Y-pipe, and put a 3" cutout right after it so you have the power of full 3" whenever you want it. I already have a 3" cutout sitting here, but I wanted to get that cat out because I think it's be setting off the CEL (time will tell if it fixed it or not).
Not sure, I think the stock Y is 2.25 into 2.5 so IDK how much it would be helping as it's still stepping it down. It would help some I'm sure as the stock is garbage, but I think even if you keep the 2.5" exhaust the 2.5 to 3 would be better. And if you plan on doing full 3" in the future you would only have to do this once. I know I'm sure getting sick of changing shit on my exhaust because I didn't go with what I wanted from the start.

I'm about an hour north of Eau Claire, GLD is a ways away for me. Rock Falls is just a little ways out of Eau Claire so that's where I would go, but not with the truck haha.
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