So I installed my ceramic coated HKS downpipe the other night without a hitch really. One of the studs on the cat stripped out, but not a big deal. What did happen though is that I now have a pretty substantial exhaust leak between the DP and cat. Is it pretty common for some aftermafket DP's to not mate up perfectly with the stock cat? Has anyone had this prob before? And if so, is the only way to fix is to get a 3" midpipe or high flow cat? Any input would be greatly appreciated. Thanks
-Sean

 

Did you replace the stripped out stud? Did you use a new gasket and torque to the proper specs? How did the mating surfaces on the two flanges look? It's such a simple connection it has to be something easy.

 

problem is the 2 bolt flanges have a tendency to bow in the center, which is probably what happened with the cat converter flange. it also depends on what type of gasket came with the downpipe or if you reused the old gasket and it isn't sealing properly or is blown out.

if the gasket is hard it won't seal up to a warped flange correctly, you can look around at your local muffler shops and try to find a softer gasket and use that or double them up. don't ovetighten the connection either or it will warp.

 

I am guilty of reusing the old gasket. I did not replace the stud, but I did have a bolt that was the correct length size and pitch. Mating surfaces seemed good. The only thing I did notice was the two surfaces seemed to not be flush after everything was tightened down. Tonight I am going to take the cat and the cat back off and put everything back together one piece at a time and see if maybe things were bound up and not aligning right. And this is no small leak either, so I am thinking its not really a gasket issue, but I won't rule it out yet. You guys know of any "common" cars or trucks that have a similar gasket that I could look for?
Thanks for the help so far

 

easiest to take the old gasket with you and match it up to one from a muffler shop, can be slightly larger at the opening but not overly large obviously. it's a pita to seal up connections when they are stepping down in size like the 3" to 2 3/4" stock pipes.

 

Did a similar install, hks coated dp but I did replace both gaskets. From what I can remember the hks did not line up and mate up to the bottom hanger under the car, it was some sort of premade piece on the old precat. If you didnt make up some sort of support at the bottom it could kink and leak. I made up something to address this, not sure if thats your issue or not.

 

Yeah, thats what my thoughts were at first, but the cat-back doesn't leak on the other side, and it's also 3 inch.

As far as the hanger for the DP at the trans., there is a bracket on the DP, I just don't have it bolted to the tranny yet. I need to make some kind of bracket/adapter for it to reach.

 

The bracket on my HKS dp connected to the transmission without any trouble. It is very important to support the downpipe. The weight of the exhaust will put serious strain on the connection at the turbo.

 

I plan on buying the HKS downpipe I bought new gaskets already but how am I supposed to support the DP?

 

It uses the stock bracket that bolts to the transmission. Crawl under the car and you'll see it.

 

also now that you ran car and got the hks down pipe hot re-tq the bolts