Akreidie1: Have you had a chance to do the "after" dyno?

Sorry i didnt get back sooner, i got stuck with lots of things to do, but hopefully by the end of the week ill have everything posted up

Thanks. I am just wondering if the gains that Brian GT PRO got was from the elimination of the secondary cats or combo of elimination and replacing with an X-pipe.

+1. Good point; the cats are usually quite restrictive in any exhaust. Hence, why some aftermarket exhaust mfgr's offer "high flow" cats (which make some HP/TQ gains) for some cars.

im interested to see this as well...

i have them ready, can any1 tell how to upload them here?

You can upload them to either You-Tube or Photobucket and insert the links on here.

What kind of straight pipes did you use? Have you dyno'd...any HP/TQ gains? Thanks.

Has anyone used this type of straight pipe to replace the secondary cats yet? I mean these things are $57 each; Brian from GT PRO insists his ~ $600 X-pipe is better and makes gains, but is that from the X-pipe or just from removing the secondary cats?

http://vibrantperformance.com/catalo...roducts_id=290

Inquiring minds want to know. The Vibrant resonator is a very high quality piece. I like Brian's idea of reversibility. If you want to be able to reuse your secondary CATs in the future, you may run out of stock piping and have to recreate the two s-bends in front of the secondary CATs. This will mean you have to buy 4 90 degree mandrel bent elbows as well.

All this "Exhaust, X-pipe, Cats, H-pipe, Resonator" talk sparked my curiosity, so, I visited a reputable local custom exhaust shop today.

And here's another question to ponder (and hopefully, someone has an accurate answer )...

Does the oem stock C63 AMG exhaust already have high-flow cats?

The reason I ask is b/c I don't think I really want to remove the secondary cats (it's illegal btw ) and thought that maybe a HP/TQ gain could be had with high-flow cats instead (if the oem stock exhaust didn't already have them in place).

So, does anyone know the specs on our secondary cats and if they are indeed high-flow cats or just plain old regular cats?

When I went to the custom exhaust shop today, the owner who's been in business for > 25 years took one look at my C63 AMG exhaust, and kind of scratched his head, paused, and said, "I'm not sure if there's much I could do here...this is a very well-engineered exhaust by AMG."

He said he could switch out the secondary cats for high-flow cats if they weren't already high-flow cats to begin with AND add an X-pipe in place of the resonator, but he has no idea about how much more sound that would produce (could be a lot more than I want without the resonator; a little more deep growl would be fine though). I mentioned to him that many ppl who removed the resonator are sorry they did, and are looking to put it back in place, and only deal with the secondary cats.

Any thoughts?

I was thinking the same thing too. ^ We'll soon know once OP post his dyno results.

Well wrote, i was thinking the high flow CATS as well, if thats the case, there is no point, then just the header and L/T from K2 then

Some HAS to know if the current oem stock secondary cats are already high-flow cats or not? This is the pertinent question.

They're not high-flow but they flow highly.

What...seriously, are you sure? How do you know this and why the play on words? i.e. - the custom exhaust shop owner said something about most cats allowing ~ 200psi and the high-flow cats he has allowing 400psi...or something to that effect. Do you or anyone else know the specs of our oem secondary cats?

where is the dyno results with straight pipes in place of the secondary cats? any power gains? i went to an exhaust shop this past weekend and asked how much it would cost to remove the secondary cats and the guy literally started laughing at me and said "you wont even be able to get up a hill if you remove it, you will have CEL warnings popping up and you will get beat by ****ing volkswagens" that is exactly what he said. i did not say a word and walked out of the shop

He must not know the O2 sensors are just behind the primary cats (way up by the DPs), not the secondary cats which are just in front of the resonator. Removing the secondary cats does not throw a CEL, and I don't think it would lose power either as you're removing 2 restrictive pieces of the exhaust...the oem ceramic (non-high flow) cats. Now, replacing these oem cats with SS high-flow (metallic substrate) cats will also do the same thing, while still having some type of catalytic converters in place.

Im sorry it took soo long guy!
but here are the b4 and after of removing second cats. The gain is 10rwp

http://www.youtube.com/watch?v=EyzvRu9HZ_Y

http://www.youtube.com/watch?v=yJiIJ12-s9s

I'd say a little louder from low end heading up, but still sounds good

Those are 2 different cars. Not a good comparative.

But it was on the same dyno, with exact same mods, and when I dyno'd it b4 it gave me 1 hp less

are you sure that there are no error messages when removing the secondary cats??? I always wanted to do it but was worried about the error signal....

Signs will only come up if you remove your primary cats, Dont worry. Remove the second.

The secondary cats do not have any O2 sensors...so how would your car know if they are missing?

+1! Just leave the primaries alone and everything else can be removed without consequences!