Exhaust Sound Change after Installing a Secondary CAT Delete Kit in an Aston Martin DB9

Secondary CAT in an Aston Martin DB9

I’ve been fiddling with my DB9 trying out several ‘Bolt On’ performance improvements.  One of them is a ‘Secondary Catalytic Converter Delete Kit’ (SCDK) which promises to:

  • Reduce weight (it does by about 8 pounds)
  • Increase Power (yet to be seen- Dyno test coming soon)
  • Improve the Sound

This article is all about the sound, and how it changes.

SCDK Installed

If you want to learn more about the SCDK I chose and why you might want to fit one, please check out my other article and video that covers it in detail (click here).

It’s not like the DB9 had a lack of power or sounded crappy in the first place.  Just the opposite.  The stock sound the the V12 engine is gorgeous.   I often don’t have the stereo on just so I can hear the symphony of cylinders while I drive.

I was also concerned not to screw up a good thing.  If the SCDK ruined it, my plan was just to bolt the original bits back on.

Removing the Secondary Catalytic Converters from the exhaust stream reduces the back pressure in the system (since its not clogging up the exhaust flow).   The converter also acts like a muffler, influencing the sound energy that passes through it.

Being able to tell you “How did it change?” is very subjective.  “It’s much more [fill in adjective of your choice] now” doesn’t really help you decide if you’d like it or not.   So, me being me, we came up with a plan….

The Before Times

Recording Rig

I enlisted my trusty neighbor, friend and cameraman Rob who’s also a bassist in a band and their defacto sound engineer to help me out.  He brought in some of his recording equipment to try and accurately record the sound before and after the change.

We setup his microphones along the center-line of the car, nine (9) feet behind the rear bumper.  The stereo mics were mounted to a stand.   We left everything setup before and after the SCDK install so the test parameters were identical.

For your listening pleasure, here is the recording of the Before sound.   In it you will hear me start the engine, let it idle for about 5 seconds, the raise the revs to 2000 rpm for about 5 seconds, and finally raise them to 4000 rpm to really hear the engine roaring.

Turn up the Volume on whatever you are listening on:

Like I said, nothing to complain about there.  Awesome.

Note:  Just donned on me to mention that I have uncorked my Aston, meaning Fuse 22 is pulled and the muffler is partially bypassed.  Did this in the first week I owned it, as have many, many owners.  Essentially this makes the stock sound a little louder in the 1000 to 3000 rpm range. Check out the article on Uncorking your Aston Martin DB9 here.

The After Times

With the SCDK installed, we setup the same test.  Idle, 2000 rpm, and 4000 rpm.   Have a listen to see if you can hear a change.

Wow!   Yes, it changed.   Picking a adjective I would say the exhaust note has more ‘Snarl’.   It sounds more aggressive, but not overly so.   It was notably louder, enough that Rob had to dial down mics input level so it wouldn’t max out during the recording.


For a more side by side comparison, here they are again, but this time I cut back and forth between them during each rev range.

If you prefer a violin and eschew an electric guitar, you might not like this upgrade.

For me I like the additional bit of Snarl, and its still plenty tame enough when toodling along at 1500 rpm most of the time around town.

Which do you prefer?   Please take a second to share your opinion in the poll.   Always neat to see what everyone else thinks!


I’ve done a quick video of the comparison if you’d like to see more about how we tested.  Check it out!


10 thoughts on “Exhaust Sound Change after Installing a Secondary CAT Delete Kit in an Aston Martin DB9

  1. Andy Evans

    As I mentioned in your early post I have this very set up since last May, and at first I was not sure about the raw sound, but it has since grown on me. Mine also pops and crackles on the overrun, not sure if this is typical or from an air leak at the defat pipes, I noted your mention of the pipes being a bit short. Great work, wonderful not ruction and analysis


  2. Jonathan Cook

    Hi did the same mod in U.K. but got my pipes from a specialist exhaust pipe fabricator for a fraction of the cost the usual sets costs. Sound is as your above. Now people know when I am about to overtake them as before on a few occasions they were surprised as they never heard me coming simply saw me fly bye.


  3. Neil Dobier

    That sounds awesome. I really like to throatier sound and love to pops and cracks. This will definitely be my next upgrade. many thanks for taking us through your journey 🙂


  4. Roger Pickering

    I’ve got a 2005 DB9 with here in the UK with 38,000 mikes on the clock.
    The previous owner had the secondary cat removed and the replacement kit is switchable…. sounding standard, aggressive, or aggressive only on higher rev range.
    Sounds awesome but to be honest I leave it in standard mode 98% of the time as I like ‘quietly understated’..
    My concern is that having removed the secondary cat I’m reliant on the primary cats…… and I’m starting to get paranoid about possible misfire and the engine ingesting the primary cats in the future.
    What do you feel are the pros and cons?
    You would seem to be completely happy relying on the primary cats…… but did you have concerns?
    Best regards


    1. Hi Roger. I understand your thoughts. The car doesn’t actually need CATs at all to operate, but to help clean up the exhaust its a good idea. One set does the trick. If you have the primary CATs removed, I would aim to reinstall the original secondary CATs, or, perhaps fit a set of high flow performace CATs in their position. Thus with the primary CATs removed and out of harms way, the new CATs in the secondary position can keep the air clean and you still get the best of both worlds.

      I have actually found a way to ‘inspect’ the primary CATs (working on a video about this with Mike from Bamford Rose). If the condition is normal and I maintain the car well, it won’t be an issue. If the condition is poor, it will raise the alarm to get them removed ASAP.


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