X force twin 3" (V8)- add a H-pipe?

[VTSSLS1]

G'day all,

I've had an X-force twin 3" cat-back for around 18 months now (mild steel), and added HSV headers and ballistic cats around 6 months ago. It sounded great, I was very happy with the sound, but once the headers & cats have carbon'd up, its lost a bit of the 'growl' and obviously a bit of volume as well. Still sounds awesome at WOT, but at light revs it's lost a bit of the burble.

It also had a rattle on cold start, which is one of the ballistic cats, which is being replaced on Saturday. Could this be causing the loss of noise? The core is loose in the body of the cat, so the rattle goes away completely once the system warms up (2 mins or so). It developed this rattle within the last month or so, hasn't been there since new.

Anyway, in case this isn't causing the loss of noise, because I'll be at the exhaust shop getting the cat replaced, I'm wondering if it's worth getting them to weld in an H-pipe to get some more burble? Just a simple 2.5 or 3" H-pipe, either before or after the centre muffler? Has anybody added an H-pipe to the X-force systems on a VE? I know it was a popular thing on the earlier models, but not sure on the effects on a VE. Would it be likely to affect drone? At the moment it;s drone free except for 80km/h in 6th gear (only in 'sports shift' mode though, not in auto). I guess I'm mainly looking for a bit more volume, and more burble, more like it was when new. Any thoughts or suggestions?

 

[Not_An_Abba_Fan]

The Manta system has the H pipe, not the X pipe, and they don't drone at all. (Calling the X Force merge an X pipe is technically wrong, as it's really just a merge pipe). It's there on the X Force system because they are drony and raspy without it. I would be more inclined to remove the front muffler and replace it with hotdogs if you want it louder. Putting the H pipe in and removing the merge will just make it sound bad IMO.

 

[Big-Al]

It could be the stuffed cat that has taken away the nice sound rather than carboning up. Get that replaced and re-evaluate.

 

[PIR4TE]

once the headers & cats have carbon'd up, its lost a bit of the 'growl' and obviously a bit of volume as well. Still sounds awesome at WOT, but at light revs it's lost a bit of the burble.

Is your tune / running all good i.e. filter, plugs, injectors? Had it tested lately? Ever had it measured on a dyno? You do realise a lot of the burble is through the cats doing their job properly, and that you can tune in more farts and burps almost whenever you want?

I'm wondering if it's worth getting them to weld in an H-pipe to get some more burble? Just a simple 2.5 or 3" H-pipe, either before or after the centre muffler?

Depends on your tune where you put an H or an X. I assume you have a CAI and tune to complement the exhaust system, and peak power is around 5300rpm: An H-pipe installation for best torque curve is at the 4th harmonic, which on your car is 480mm along the centreline (before the centre muffler) measured from the end of primary tube ends (bottom of the tri-y flange).

For torque on your VE I'd stick with the X-pipe but have it after the centre muffler intersecting at 1920mm measured from end of primaries. That is the exact point of the second harmonic, ideal for torque and hp, and reducing unwanted harmonics (drone).

My car develops different peak power, so no haven't done exactly as your specifications and, (by coincidence rather than catback design) the x-merge on my X-Force is at the second harmonic, 30cm further forward than your ideal placement.

 

[VTSSLS1]

Not yet tuned to suit, just the exhaust at this stage. I think I'll go with Big-Al's advice for now, wait and see if the new cat affects things. Might look into pirate's advice in the future though, you certainly know your stuff.