Hi guys,

In a few weeks I'm gonna be welding up my 2.5" downpipe and 3" cat and exhaust. I was going to buy a 2.5" to 3" SS transition pipe to weld onto the front of my cat or the back of my DP, but now I've decided against it. I have two extra 3" flanges that I can use instead. Now I looked at my 2.5" DP flange and 3" cat flange and it *looks* like I can just bolt them up together and not have to worry about an exhaust leak.

However I was thinking about doing this for my DP instead. I can weld my 2.5" pipe to the 2.5" flange. Then I would line up the 3" flange behind the 2.5" flange and weld the seam between the two flagnes so there is no chance of an exhaust leak. So now I would be able to bolt up the cat's 3" flange to the 3" flange on the DP.

what do you guys think? I think it's better this way cause I dont have to worry about buying another transition pipe, I can just use one of these extra 3" flanges I have.

 

i dont see why not. id assume that aslong as the 2.5" flange covers the hole on the 3" flange it would be possible. dont expect great flow though

 

Yah the holes line up and everything. But I dont think flow will be affected too much at all. I could weld a bead on the inside and grind it so that it is angled. That way when the 2.5" pipe goes to a 3" cat it will slope instead of going straight from 2.5" to 3".

 

why not a step it with a 2 3/4 or sumthin

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by JCushing &raquo;</TD></TR><TR><TD CLASS="quote">why not a step it with a 2 3/4 or sumthin</TD></TR></TABLE>

Because I have these 2 extra 3" flanges and I might as well use them. Why buy a transition pipe for $10-$20, when I can just use a flange which I already have?

 

Flare the end of the 2.5 to 3"

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GS-Rcivic &raquo;</TD></TR><TR><TD CLASS="quote">Flare the end of the 2.5 to 3"</TD></TR></TABLE>

that's how my downpipe is...

2.5" and at the very end it is flared to fit a 3" 2bolt flange.

 

the 3" will reside with the 2.5 hoever it will leak. theres usually not enough material around the bolt holes and the 3" will leak in those areas.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by project dc2 &raquo;</TD></TR><TR><TD CLASS="quote"> the 3" will reside with the 2.5 hoever it will leak. theres usually not enough material around the bolt holes and the 3" will leak in those areas. </TD></TR></TABLE>

yah, the 2.5" flange has oval bolt holes while the 3" flange has circle holes. The inner part of the 2.5" oval bolt hole come very close to the inner part of the 3" pipe. So it looks like I will have to weld a bead on the inner part of the flanges to help prevent leaking from the piping to the flange bolts.

 

Why do anything, I welded a 3" pipe to a 2.5" pipe without touching either piece. of course it took 3 beads to do it but it worked fine.
Something else I did was use a 2 1/4" flane and a 3" pipe, used a 2 1/2" pipe between tho.
Oh I work at a custom exhaust shop, i get creative when doing stuff.