3 inch Downpipe Tied Into Stock System?

[LegacyT]

Hi there,

If I say, purchase an HKS 3 inch WRX downpipe, could I tie it into the rest of the stock exhaust system? I hear the stock downpipe is the single largest restriction in the whole system. The reason is that I want some performance gains without spending a whole load of cash on the car.

Thanks,
Mark

[DLC]

Any exhaust shop should be able to remove your stock DP, install the HKS one and weld on a proper sized flange to the stock midsection, if needed. It might take a little work, but it will work, though going 3" -> 2.25" (or whatever stock midsection is) might not be the best idea.

Dave

[billc]

I agree with Dave about going from 3" to 2.25".Think about a water main feeding into a garden hose.However, the stock downpipe seems oddly bent and it has a cat con built into it. It is also very heavy. I noticed a nice difference when I replaced the stock downpipe with a gently bent straight through downpipe. Even with stock midpipe and cat con the power increase was noticeable. You could then increase exhaust flow as cash flow increases. That is what I did. Replacing the muffler also made a difference.So in my opinion, that would be next.When I made a midpipe without a cat I noticed almost no difference, so I would do that last. I actually put the stock one back on because of eco-guilt.I guess I should mention that my downpipe is 2.25dia, just much lighter and free flowing than stock,as was the midpipe I made.A 3" midpipe might make more of a difference,especially with that 3" downpipe.Anyways,just relating my experience with the exhaust on the turbo Legacy. Hope it helps. BillC

[-K-]

I don't think it could hurt, getting rid of the stock DP-cat is going to be great. Then work back as the cash is there. How much is it? I could get a DP and full system made for less than $500. If you look around and find a good muff shop they can make a real nice system much cheaper than getting a "bolt on exhaust"

[IggDawg]

I'd just like to mention a lot of people around here have been passing emissions without any cats at all. They can't dyno our cars, so they just rev to 3000 which puts NO LOAD on teh engine. Also, many people run straight pipes both here and in the WRX community with no problem. I personally know a couple guys who have been without a backbox for the better part of a year now without a problem. I'm definitely going to go for a 3" catless downpipe soon (and keep the stock one just in case), and then a 3" dtraight pipe and midsection. I'm pretty sure a nice simple catless 3" system won't cost too much fromthe local Minake.

[GizMo22t]

I orderd a 3in high flow cat and a 3in muffler on friday the 28th.I hope to see them on monday. I will have pic's here when I get the pipeing done and let you all know how well and how much I spent. So far the Highflow cat was $120 and the Muffler was $169. I don't expect the pipeing will be any more than $200. But you never know.

[-K-]

What brand, kind of muffler. I hope it is straight through.

[GizMo22t]

It is a Magnaflow straght through design. I had one on my last car that was turbo'd it worked greaght.

[eastbaysubaru]

Eventually I'll be doing basically the same thing. I'm going to get a Magnaflow muffler and some sort of WRX downpipe and tie them all together with custom made piping, including a resonator. My friend in Newport Beach has TONS of connections down there, one of which is Magnaflow. I'm fairly sure I will be able to get any Magnaflow stuff at cost. Too bad I have absolutely no money right now.

-Brian(looking toward the future)

[lgyee4]

Absolutely a great way to go! you may have difficulty in finding reducers from 3" to what ever the stock size is and have it fit in before the first catalitic converter. A thought may be to go 3" trom the turbo to a 2 1/2 inlet cat. then after the cat, reduce the rest of the way to the stock pipe diameter.

[eastbaysubaru]

I think I'll be doing a 3" d/p and 2.5" for the rest of it.

-Brian

[-K-]

Yeah thats what I'm thinking. 3in DP get a nice long header reducer to 2.5in in to what cat??? I'm actualy thinking about running a dydomax bullet where the cat would be, keep it low key untill I'm on it hard.

[subiekid]

all the guys that i have talked to said it would be best to go from a 2.5 dp then go into a 3 inch system so it gains velocity as it goes. I was thinking you would have some backpressure right at the section of 3 to 2.5. I am gona go with a full 3 inch turbo back. I heard that the hks dp is not very good, but it woudl be better then stock, i want to get the perrin or stromung. then have a custom mid pipe made and tie it all off with a dual tip stromung muffler with 3 inch pipe. I want to have 3 inch pipe for the mid and run one high flow cat. all on my 95. right now i have the stock with a borla muffler.

[Legacy777]

subiekid I think you got something mixed up.

If you go with a 2.5" to a 3" exhaust velocity will decrease

Velocity is inversely proportional to volume.

Personally....I'd go with a 3" down pipe and the remainder piping somewhere between 2.5"-3" Depending on turbo size and boost running.