i just need to know stock ss/sc downpipe diameter size. im pretty sure its 2.25 but ijm not completely sure.

 

Its over 2.5in, I can check when I get home in like 20min since its sitting in my basement. I think its closer to 2 3/4 in.

 

the inlet is a 3" flange yet the flex pipe cuts it down to about 2.75"
outlet 2.5"
piping im not sure but the stocker is bad for flow because of the flattened part for the O2 bung and the cat...the exit is debatable

 

i just needed to know because i used the LSj downpipe on my Ls. turned out pretty well. definately a cheap upgrade for the base model anyways.
im backed by the ss/tc catback so i guess i have full 2.5 in exhaust, just need aftermarket header now

 

The approximate O.D. of 90% of the stock downpipe is 2.785". The inlet flange is 3", but necks down to 2.25" before entering into the piping before the cat. The neck down portion right before the 2-bolt exit flange is 2.345" O.D.

 

I'm looking for a universal high flow cat to buy but i cant seem to find out what size to get to replace the catalytic convertor for a 2007 ss/sc. I read it was 2.25 and then some where else it says its 2.5?? help please

 

Try the company cannamex (if i spelled that right) This is where ZZP gets there high flow cats from.

 

to replace the cat in the stock dp you'll want 3" iirc


i can go measure mine right quick(sitting in the trunk waiting to get re-installed)

 

If the stock downpipe is that big then why is there performance to be had with a 2.5? Just because of the high flow cat?

 

Is your cat bad or damaged?

If not, don't waste your money. The stock lsj downpipe comes with a high flow cat as is, and your gains going to an aftermarket one will be minimal at best.

The stock lsj downpipe has a high flow cat, but it has some restrictions elsewhere....

The main restrictions are at the O2 sensor, and inlet flange.

The inlet flange starts out at 3" then necks to around 2" than back to around 2.75". The pinch at the O2 sensor crushes the cross sectional area down a bit as well. The outlet of the downpipe is actually a little smaller than 2.5" more like 2.354" from my measurements.

 

Would you say a 3" downpipe is the best choice even if you have a 2.5" catback?

 

I run a 2.5" downpipe & flow a good amount of air with my setup. It works well on my car.

I've also tested 3" downpipes, and really didnt notice much of a difference over my 2.5" downpipe. The 2.5" downpipe will have better exhaust gas velocity and great flow. While the 3" might flow a bit more, it wont have as much velocity due to larger piping (unless you are flowing a large amount of air). A full 2.5" exhaust is ideal for most if not all M62 setups. 3" piping is really not needed until you are making a decent amount of power.

 

Oh Well, I got ZZP 3 inches catted 2.5 exit, for my 2.9 and 50lbs fuel injectors. But I haven't put in 50lbs and downpipe yet til I get NEW ZZP 2.5 exhaust with 3 chambered muffler. I am still on 42lbs and stock header to exhaust. Can't wait!

 

yes my cat has tears on it causing the check engine light to come on and the noise it makes is just annoying so im looking for some type of cat that will fit on..bolt on or universal...that will eliminate the problem and at the same time give me performance. So far everything on my 07 ss/sc is stocked except for the 2.5 catback exhaust.

 

Good question. I'd like to know the REAL answer to this. i went ahead and got the 3" but always wondered if it was necessary.

 

Magnaflow Catalytic Converter - Magnaflow 53100 - Natural, Minor modifications required, 49-state legal.. i found this one but im reluctant that it wont fit or its just not a good fit..any suggestions on this?

 

I believe 3" Stainless Cobalt Downpipe with 2.5" exit will be a direct bolt on. ZZP sells them at a good price. if you do 3" inlet and 3" outlet on the stock exhaust your gonna have to have it welded on. Also if you return ZZP your stock cat they give you $50 toward your next purchase.

can anyone else confirm the direct bolt on size of 3" inlet to 2.5" exit on the downpipe.

 

huh