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2-1/2" Downpipe for 1g Fwd?

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91Bomb

15+ Year Contributor
909
7
Jul 15, 2003
US, New_Jersey
Just got a DP today but looks like it won't bolt up since outlet is 3" and my test pipe is 2-1/2". Checked ebay (and other places) and don't see any DP's with 2-1/2" inlets + outlets. I can't change test pipe either because it's bolted up to stock exhaust and don't want to mess with that. I don't even see 2.25" dp's. All I found are stock 2" alluminized or 3" stainless. Anybody have thoughts on that?
 
A reducing flange might be good but I can't find 3" to 2.5" 2-bolt like the one in your pic. (I'm also concerned about the extra length causing problems).

Checked out VRS but their alluminized 2.5" is $55 more than 3" Megan stainless I just bought and their 2.5" stainless is $125 more.


PS: Is 3" DP on my mildly free-modded car a detriment in any way? Because I'm only running a couple lbs over stock with no plans on going much higher (if at all). When I went from stock 2" to current 2.5" it seemed like a good move but worried 3" might not be. Mainly asking because if I do keep it I'll probably have to get muffler shop mate it to my 2.5" tp and then I'd be stuck with it.
 
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To answer your question:
No, a larger diameter down pipe will not hurt performance. The less back pressure, the better.

It would be better to have the test pipe Modified by a shop that can weld to mate the down pipe to the rest of your exhaust if you do not like either of the other options given. This way, if you decide to finish the rest of the exhaust, you won't have more custom work later.
 
I might just return it and get a 2-1/2". Looking for a good used one or might get VRS alluminized one. There's no good cheap options for 1g fwd 2-1/2" I'm aware of.
 
One last question, is it better to keep the 3" stainless DP but have it mated (via reducer) to 2.5" TP (rest of exhaust will be 2.5" too) or get the 2.5" alluminized DP so whole exhaust will be the same diameter.

Mainly wondering if keeping an exhaust system a uniform diameter is more desirable plus car will never see more than 275 hp for sure. (15 lbs boost is the most with this motor or perhaps 17 lbs if motor ever gets rebuilt).
 
Anyone know if I should be able to get o2 to downpipe studs at local auto store? Don't really want to pay $8.95 plus shipping from dsm vendor.

I believe stud size is 12x1.25x28mm but is there a certain grade of metal to get? Should I use thread locker so stud doesn't come out when loosening nut or just use anti-seize on nut side?
 
Returned 3" stainless and got VRS custom made 2.5" mandrel bent Downpipe ($205 shipped).

Length is good but flange didn't line up with TP and that may be my fault from previous work but not sure. Wound up cutting flange on pipe just after TP so I could rotate + reattach it so everything bolts up.

It didn't come with front or middle hangers like stock DP's but fit seems good and doesn't seem like it will be an issue maybe because flex section is shorter idk but on car it appears solid.

Not sure about the looks of these welds or is that possibly just a rust inhibitor coating making them look that way?

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One last question, is it better to keep the 3" stainless DP but have it mated (via reducer) to 2.5" TP (rest of exhaust will be 2.5" too) or get the 2.5" alluminized DP so whole exhaust will be the same diameter.

Mainly wondering if keeping an exhaust system a uniform diameter is more desirable plus car will never see more than 275 hp for sure. (15 lbs boost is the most with this motor or perhaps 17 lbs if motor ever gets rebuilt).
Why so little? High miles? I've seen tired 6 bolts push 19-20psi for years with no issues. They didn't constantly beat on the car tho.
 
Why so little? High miles? I've seen tired 6 bolts push 19-20psi for years with no issues. They didn't constantly beat on the car tho.

I'm on a budget and sticking with free/cheap mods now plus doesn't take a whole lot to get 1g Fwd's moving down the road.

Anyhow, anyone want to comment on my new 2.5" Downpipe (2 posts ago)?
 
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I'm on a budget and sticking with free/cheap mods now plus doesn't take a whole lot to get 1g Fwd's moving down the road.

Anyhow, anyone want to comment on my new 2.5" Downpipe (2 posts ago)?
the welds are kinda shoddy butlook like they'll seal. Explain your situation to the vendor and have them send you a new one if you don't like it. Most are happy to oblige if it's their fault
 
Yeah I was thinking about sending it back but it's on car now so guess I'll live with it.

Btw is there a vendor review section here so I can give a write up on it?
 
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