2.5" DP and Magnaflow--RESULTS UPDATE - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 08-07-2007, 10:33 PM   #1
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Default 2.5" DP and Magnaflow--RESULTS UPDATE

Bought a 2.5" DP (with welded-on H-Body flange) and Magnaflow cat from a BC member:
http://www.bonnevilleclub.com/forum/...ic.php?t=80900



Also bought 3 AccuSeal Clamps on EBAY, and rented a chain-type tailpipe cutter from Autozone. Also got some sealant in case of leaks. My new buddy at the muffler shop gave me a 14" length of 16-gauge 2.5" OD stainless exhaust pipe in exchange for a smoke and a chat about baseball.

Cat'* ID measured 2.58", while OD on the DP and pipe were 2.50"...had to cut some slots with a hacksaw to make sure the clamp would close it all the way:



All I have to do to the new parts now is cut that rear pipe down to size:


Install pics hopefully coming this weekend
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Old 08-07-2007, 11:54 PM   #2
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Awesome, ANdrew.
Can't wait to hear how it runs with that in place.
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Old 08-08-2007, 04:50 AM   #3
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Got the chance to start the install this evening.

Best shot at the rear mani to DP nuts was from underneath:



Then the DP flange to cat nuts:


Maybe a week or week-and-a-half ago I cut the pipe holding in the cat just behind the weld with the chain cutter, and I've running with an AccuSeal clamp holding that together since then:



(I also went through and PB Blasted / loosened / retightened all the nuts involved in this install at that time, just so I'd be ready when my parts arrived )

Here'* the naked rear manifold studs, with lots of anti-sieze applied and re-using the metal DP-to-mani gasket:


New DP looks to fit fine with plenty of clearance. Yay, the stock cat fits onto the new DP and back into the resonator...



Good thing, too...the 2.5" OD straight pipe on the back of the new cat is just a wee bit too big to fit into the cut-off resonator pipe; I think the AccuSeal clamp might have crushed that resonator opening down a touch...I'm going to have to rent a tailpipe expander to open up the neck of the resonator before installing the cat. That'* OK though...I kinda wanted to see what the DP alone does, THEN the DP plus cat.

Here you can see the size difference between the stock cat and this Magnaflow


More to come!
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Old 08-08-2007, 08:55 AM   #4
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Looks great Andrew...

Did you cut in front of the O2 bung?
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Old 08-08-2007, 12:09 PM   #5
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Quote:
Originally Posted by BillBoost37
Looks great Andrew...

Did you cut in front of the O2 bung?
No, behind. The new cat and pipe is bungless, and I'll program out the rear O2 with the tuner.

The stock cat w/bung will be swapped in for special occasions
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Old 08-08-2007, 01:53 PM   #6
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Ah, dang it...."pfft, pfft, pfft" on the way to work today. I can't make it happen just revving in the parking lot...only under load.

I hope the leak turns out to be at the stock cat-to-resonator joint, where I can fix it up temporarily with some sealant (and perhaps more permanently later).

If this DP is leaking (at the flex?), I'm gonna be an unhappy person .
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Old 08-08-2007, 02:04 PM   #7
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It'* leaking somewhere where the engine causes two pieces to pull apart. Maybe your neverseize(it looks like anyways..) let the flange nuts to the manifold come a little bit loose?
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Old 08-08-2007, 02:44 PM   #8
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Quote:
Originally Posted by MyLittleBlackBird
It'* leaking somewhere where the engine causes two pieces to pull apart. Maybe your neverseize(it looks like anyways..) let the flange nuts to the manifold come a little bit loose?
I did just go take a look under the hood, and it looks as if the left side mani-DP stud is not in as far as the one on the right side...I did remove and re-install those studs (7mm hex head) before installing the new DP, but maybe I didn't get that one seated all the way. Will check that out this evening. Also, perhaps I was a bit too liberal with the anti-sieze

In any case, I did rent the tailpipe expander, so maybe that new cat will be on sooner than I thought...assuming I can find and fix this leak
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Old 08-08-2007, 10:34 PM   #9
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hope you get that leak fix youre cat look the same as the new one i got you should see difference in sound and power
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Old 08-08-2007, 11:24 PM   #10
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More progress; got the cat and pipe clamped in between the new DP and resonator:


Drove it around a bit, and it does feel like it accelerates more freely...unfortunately I couldn't find a place to really open it up due to traffic. Oddly, no codes were thrown even with the rear O2 gone...maybe they require 2 or 3 startups.

The sound I was hearing is still there. I'm beginning to think this is the downpipe flex "ticking" I read about on the ClubGP forums...anyone familiar with that? Supposedly it'* not a leak, but rather the sound of the valvetrain amplified in the single-walled downpipe (???)

Anyway, supposedly this flex ticking can be addressed by using header wrap around the flex. (Does this actually fix it? Who knows...nobody ever follows up threads on ClubGP with testimony regarding success or failure )
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