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Discussion Starter · #1 ·
I was reading some posts on the SoCal DSM list and someone mentioned that they decided not to get the Thermal R&D 3" Exhaust because of the fact that the flange that connects the lower pipe to the cat is only 2 1/2 inches. When I bought my Thermal Exhaust, I didn't realize this fact up until now.

I had been planning on getting a 3" DP and 3" high flow cat to go along with my catback, but now it looks as though the 2 1/2" flange on my catback is going to be a restriction. Now here's what I can do:

1. Get a 2 1/2" DP and cat and let it open up into 3" at the catback

2. Have someone weld a 3" flange to the back of the thermal catback to fit the 3" cat

3. Get a 3" DP and 3" cat then a 3" to 2 1/2" adapter to fit the catback

Would idea #3 work well at all? It seems that a 2-3" section of 2 1/2" piping wouldn't be that much of a restriction, and would save me the $ of having someone weld a 3" flange on it. I've already dropped $550 on the exhaust + $60 for adapter plates to get it to fit correctly and it really sucks that I'm going to have to spend more on it to get the DP and cat that I want.

Finally, how much would welding a 3" flange on it generally cost?

Thanks,
Marlin Liew
97 GSX "Phacade"
 

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I would advise against going from 3" to 2.5 to 3". That is just sloppy either go 3" all the way or don't. When I had my exhaust done I just had the exhaust shop chop off the 2.5" flange and pipe section, then expand the pipe to fit over the test pipe and then weld it up. The entire exhaust install and welding was $100, but it is quite easy to weld up a flange on your own. Go with choice #2
 

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Depends on what kind of hp you are after...
Number 1 is good. That is what I have.
Number 2 is better if you are going above a big 16g turbo, I've heard.
Number 3 is not good!

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Rocky Mountain Talon - modified
Live, Learn, Love and Bleed DSM...

My DSM
 

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yeah..I got the thermals too. i was disappointed about the 2.5 part but thats okay. I suggest you do #2. Thats what I'm planning on doing. it shouldn't cost that much to do. plus, like Fatass92 says, go 3" all the way or don't. i just gotta get the downpipe and cat first. have you decided on which ones your gonna get?

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Ray
1998 Eclipse GST
Mods: 3" Thermal R&D, Greddy TypeS bov, Greddy IC Piping, Magnecores, dump tube removal, MBC, Sprint Lowering springs, strut bars, Autometer gauges, HKS timer, custom interior, 17" performance rims

 

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For sub 500 hp goals i would say its best to use a 2.5in downpipe and a 3in cat. A three in cat will be much less of a restriction than the 2.5.

just have a muffler shop cut and weld a new flange, or just weld the cat to the catback.
 
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