Pairing 3" DP to 3" catback

[Qwoz]

Quick exhaust question. I am thinking about getting a 3" catback system to match my 3" DP. If I get the 3" catback should I have an exhaust shop take out the 2.5" section where they would mate with a clamp? Since both pieces are sold to mate with the rest of the stock exhaust, would it be beneficial to have them modified so its just straight 3" to 3" instead of 3"-2.5" connection- 3". I am assuming the answer is yes, but I would like some input. Thanks!

Also if anyone is looking to sell their 3" catback or know of any deals please let me know!

 

[Red5pade]

was the dp modular? if so, just bolt it up

 

[nashbar]

3" to 3" with a v-band clamp, make your life easy

 

[Qwoz]

3" to 3" with a v-band clamp, make your life easy

So just saw off the section that goes from 3" to 2.5 on both the DP and catback? That would leave probably a 4-6 inch gap between the segments.

I'm talking about the part of the DP that is like 4 inches long at least and goes from 3" to 2.5". It would be the same on the catback.

 

[Qwoz]

Here is a super sophisticated diagram I drew up in CAD. Notice how there would be a restricted 2.5" segment without cutting. Should I cut at the gray lines to pair them together in order to remove restricted area?

 

[sirsycott]

Here is a super sophisticated diagram I drew up in CAD. Notice how there would be a restricted 2.5" segment without cutting. Should I cut at the gray lines to pair them together in order to remove restricted area?

sure why not? what can go wrong?

i'm actually curious

 

[Cryptic1911]

not worth the hassle. Mine is like that, and it runs like a raped ape

 

[Tutti57]

Not a problem running like that. I did it with mine and now have 3" the whole way and nothin changed.

 

[Qwoz]

not worth the hassle. Mine is like that, and it runs like a raped ape

I'm confused, you mean you cut out the restriction? and I can't tell if running like raped ape is a good thing lol

 

[eurocars]

Just do it right and run 3" through the whole system. No sense in half-assing it

 

[Cryptic1911]

I'm confused, you mean you cut out the restriction? and I can't tell if running like raped ape is a good thing lol

no, I've got the 3-2.5-3 setup that was described above. That short section of 2.5 most likely isn't going to introduce enough of a restriction to make any noticeable gains if removed

 

[xatnys360]

I did this and while I do not doubt that the restriction isn't a big deal, it droned HORRIBLY between 3-4k RPM. I did what the OP proposes - I went to an exhaust shop and had them cut off the 2.5" section and weld up 3" (I actually used a Dynomax straight-thru resonator). You can still remove the whole thing easily enough as the downpipe has a V-band a couple feet up and the catback has a V-band at the first bend towards the muffler. The shop charged $50 and the drone disappeared completely.

OP, my only suggestion would be mark everything while its in the air and then remove the pipes before they do the work so you get a better weld. If they do the work while the whole unit is on the car, it'll work, but it won't be pretty (especially up top where they have very limited access).