Reduce booming noise between 2200 and 2800 RPM

[phn]

My Chim 450 has always been rather loud between 2200 and 2800 RPM where the exhaust note becomes quite "boomy".

This can get quite annoying on a long drive (2800 rpm being around 70 mph) and gives me a headache sometimes.

Below 2200 RPM or above 2800 RPM the exhaust note is much better.

I have had the exhaust checked over and the wadding replaced in the main silencer (the old stuff had practically burned away) but the booming sound is still there.

For info I also checked the sound levels roughly (with a mobile phone app so probably not fully accurate) and got the below readings 0.5m from the exhaust.

Idle = 91db
3000 RPM = 102.7db
4000 RPM = 104.5db

Is this the same for all Chimaeras or is mine just extra noisy?

[Milky No Sugar]

Which Y piece do you have in?

Are the pre cats and main cat still there?

[phn]

The engine looks like it has the standard factory fitted exhaust with cats.

[Classic Chim]

But if those decibel levels are to believed you’d have to have a decatted Y at least.

My 450 Catted is 94db at 4000 revs with pre cats removed using a track noise monitor placed at the end of tail pipe.

[phn]

Thanks, no wonder it's giving me a headache - I'll get someone to look at it.

[Tyre Smoke]

If your Y piece is a decat pipe, I might be interested in buying it from you.

[Milky No Sugar]

If the main cat has been removed from the standard y piece with no additional cone or internal changes, I understand this causes a boomy, almost agricultural sound. You may just need to change the Y Piece.

My 500 had a Clive Ford Y Piece (no cat) and had the pre cats removed with a standard silencer, and it did not sound unpleasant nor boom at any rev range.

[QBee]

No question, those decibel levels are de-catted.
Mine with a Clive Y and precats out was around 105db.
Add a turbo in place of the Clive Y and it's 92 decibels.

Booming, as said above, is because you now have a dustbin for a Y piece with no cat in.

Do the swap with the guy who offered.....and sanity will be returned.

[Tyre Smoke]

I didn't offer a swap!

I said I might be interested in buying it. However if it's just a decatted Y piece, then no.

[geordiepingu]

Classic Chim said:

My view is the extra hp gain but loosing a bit of torque is simply not enough to justify the noise. On a standard car I think it makes the car slower all the way up until you get into hp territory which isn’t really until about 4500 revs. Many cars rely on the torque to yank you up the road not the hp which is small until you hit high revs.

What you're effectively saying here is you need to drive it like a big MX-5 ;-)

Giving away power band setup now!

[QBee]

geordiepingu said:

Classic Chim said:

My view is the extra hp gain but loosing a bit of torque is simply not enough to justify the noise. On a standard car I think it makes the car slower all the way up until you get into hp territory which isn’t really until about 4500 revs. Many cars rely on the torque to yank you up the road not the hp which is small until you hit high revs.

What you're effectively saying here is you need to drive it like a big MX-5 ;-)

Giving away power band setup now!

I do sometimes think of my Chimaera as being an MX5 but with "sufficient" torque, a la 6.75 litre Rolls or Bentley

[phn]

Thanks for all the replies - very interesting - I'll ask my garage to take a look at the Y Piece (which on the outside looks standard) and see if someone has removed the internals.

[Tyre Smoke]

In that case, I don't want it. If it was a proper decat Y then I'd be interested.

[Tuscanuwe]

If the exhaust hanger (rubber mounts) in the back are fitted too tight, this will cause booming.
The vibrations from the engine will go through the exhaust system and if the exhaust system
is tightened too hard to the car body it will cause vibrations. The booming are vibrations