Hi

I am have 06 C4S with SuperSprint Racing Exhaust and H&N Cold In take

If I want to improve the sound,

should I upgrade the header with X51 header or Fabspeed Cat bypass?

both of them are around US$800

 

Cat bypass will definitely make your car louder. Not for everybody, so see if you can get some sound clips from members here. I have the X51 headers on my car and sound improvement isn't that noticeable to be honest.

 

AWE 200 cell cats are AMAZING for the sound and power!

 

Hey ct-andy, the catbypass pipes will give you some more power in the mid range and on, but they will sound louder and more aggressive. You loose a little power down low, but it picks up quickly once you get into the higher RPM's. Silver329 is correct, you wont notice a big difference with the x51 header upgrade. If you don't want too much sound, but a nice power gain, take a look at our 200 Cell Sport Cat X Pipe. PM or email me if you have any questions.
thanks,

 

Why not muffler bypass?

 

+1 on cat-bypass, it really opens up the sound at top end.

With PSE on loud mode, even the GT3-RS guys think mine sounds great.

Picture of my custom made X-pipe style cat-bypass very simlilar to fabseed and akropovic design

 

Would a gundo + xpipe be ridiculous loud?

 

Gundo + Cat-bypass is too loud in my opinion.

Since my car has PSE and in loud mode it is similar to a factory muffler after Gundo hack.


This gives you a sense in terms of volume: PSE (quiet mode) + Cat-bypass = PSE (loud mode) + factory cats

If you are going for high flow cats, you will probably want to do Gundo to have a good aggressive sound.

I would suggest you do the cat-bypass first and then the gundo if you decided to go with cat-bypass.

 

do you get a CEL with hi flow cats?

 

yes even with mini-cat to fool the O2 sensor, a proper tune should take care of it.

My Softronic tune is on the way,,

 

So do you need a tune to run the hi flow cats to take care of the CEL?

 

Using the right 200 cell cats will not give you any CEL. The O2 sensors are properly positioned so there are no problems. I loved the sound of my Targa4S when I had PSE plus X51 headers plus 200 cell cats. Don't know what the X51 contributed, if anything.

 

so what are 'the right' ones - HJS?

 

I think mine were AWE second generation cats, where they extended the O2 sensor mounts. Others here may have more specific info to differentiate the right ones.

 

I've been running my AWE HJS cats for 2 years and have yet to see a CEL.