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[duggs]

Saw a friend of mine earlier today who owns a facelift, 3.0 MV6.  He mentioned that the car was a bit loud from the middle back...the previous owner had made some mods.

After a ground inspection it turns out that one of the mods was to remove the rear box entirely, running new stainless pipes all the way, unhindered from the back to the two "mid" boxes.

We are assuming that the resulting noise is obviously because the rear box is missing BUT are curious at to what the benefits of doing so are....it passed the MOT like that so we equally assume its legal.

Any thoughts please ?

[rob in gib]

Copied this from mot testers manual

Method of inspection

b. assess subjectively the effectiveness of the silencer in reducing exhaust noise to a level considered to be average for the vehicle

Reasons for rejection

       b. a silencer in such a condition, or of  such a type, that the noise emitted from the vehicle is clearly unreasonably above the level expected from a similar vehicle with a silencer in average condition


So basically it is at the mercy of the testers ears
hth

[Tony H]

Saw a friend of mine earlier today who owns a facelift, 3.0 MV6.  He mentioned that the car was a bit loud from the middle back...the previous owner had made some mods.

After a ground inspection it turns out that one of the mods was to remove the rear box entirely, running new stainless pipes all the way, unhindered from the back to the two "mid" boxes.

We are assuming that the resulting noise is obviously because the rear box is missing BUT are curious at to what the benefits of doing so are....it passed the MOT like that so we equally assume its legal.

Any thoughts please ?

I'm suprised at that the backbox fell off mine a while back, the noise was load enough to wake the dead  As for benefits all I know is some engines require back pressure for maximum efficiency. I don't think you will get an improvement in flow as the main restriction in the GM V6 is the manefold

[duggs]

BUT with the lack of back box is he gaining or losing HP.

[U]

is there an ACTUAL proof, except sound, that power/torque, at least, CHANGED?

[waspy]

It sounds faster so therefore it is faster

Actually removing the cat & most of the restriction from my diesel has made it more responsive & quicker
My old Trans-Am didn't have any silencers as such 8-) 8-)

[dave10]

removing the back box is better for any car aslong it is replaced with a legal substitute (ie passes emision test)
simple test i tell people blow hard as you can then try blowing the same through a straw you are restricted thats what an engine feels like as for noise its classed as a fly by noise just like a plane

[Bixy1]

The back box fell off the wife's diesel Astra. I replaced it with a straight through pipe from srapyard. Been like that now for 4 years. No probs with MOT. Noise is not much louder than normal!  :-?

[waspy]

The back box fell off the wife's diesel Astra. I replaced it with a straight through pipe from srapyard. Been like that now for 4 years. No probs with MOT. Noise is not much louder than normal!  :-?

Is the Astra turbo'd? If yes, the turbo supresses most of the noise.