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Discussion Starter #1 (Edited)
So, I went to day and updated my L61 Header and Downpipe to an LSJ. I've seen alot of posts about this being "a cheap upgrade mod". And it is. I got my Header and DP for $125, and with a little machining work to the studs, and all new Gaskets, I have $200 in a better exhaust.

There are some major differences between the L61 and LSJ Header.

DownPipe: Flange to Cat:
L61: 2-1/4"
LSJ: 2-3/4"

Downpipe: Cat to o2 Sensor:
L61: 1-7/8"
LSJ: 2-3/4"

Downpipe: After O2 Sensor:
L61: 2"
LSJ: 2-3/4"

Header to Downpipe Port opening
L61: 1.9" x 1.6" D shaped
LSJ: 2 1/4" Round

L61 Header:



LSJ Header:



Comparison:



LSJ to L61 Downpipe:



It sounds louder and lower exhaust note. This is hooked to a GMPP Cat back.

I will be dyno'ing the car Saturday, at which time I will be able to list whats gained, as my car was last ddyno'd in April, and this is the only performance mod since then.
 

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Holy crap - the differences are tremendous! Too bad the downpipe won't fit my auto car. :(

I'm pretty sure my stock downpipe is KILLING me.
 

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haha welcome to my world, i need the down pipe to complete my exhaust!
Yep - I've basically just planned on buying a header and according downpipe. Going to have to have whoever make it without a flange at the end so I can weld my 3-bolt to it.
 

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There are a couple 3 bolt flange header's on EBay for under $200...mad bad header or something. I was gonna buy one but I said nay and got a header/DP combo from a local and bought a catback too...just gotta take an afternoon to install it all.
 

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Just to clarify: The "D" shaped opening is on the 05 and 06 Cobalts with the non-SAI equipped 2.2s -- in 07 the exhaust manifold was changed and looks more like the LSJ/LE5 exhaust manifold (The O2 sensor is not in the exhaust manifold on the 07+ 2.2s). Also, the LE5 shares the same exhaust manifold with the LSJ -- so you can get one off a 2.4 if you can't find an LSJ.

The DP on a 2.4L is larger than the 2.2L DP...and the LSJ DP is larger than the 2.4L DP. But they are not interchangable between manual tranny and auto tranny without some alterations.
 
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