Thought I'd give a review for anyone contemplating on hi-flow cats for their V12V. So far, this is the only modification that has been done to my V12V.
I purchased 100 cell race cats, after discussions with Stuart Dickinson.
I have accumulated approximately 1600 kms (about 900 miles) of driving, and about 8 start cycles since installation.
Initially they were quite loud; not obnoxiously so, but about 15 - 20 decibels in increase at cruise with a 25 - 30 decibel increase at high RPM's (the sound levels will eventually decrease; read farther down). The car sounded extremely aggressive & mean, similar to a factory scuderia set-up with lots of pops & crackles on deceleration and an extremely aggressive bark upon start-up.
There has been absolutely no drone at any speed.
Power wise there is definitely a seat of the pants increase, but I have not dyno'd the car to be certain. The car tends to overpower the traction control now on the 1-2 & 3-4 shifts when your not careful.
After about the fourth start cycle, the car has definitely quieted down and appears to now be only slightly louder than factory.
I believe that the computer has been through enough learning cycles that it has now accommodated for the hi-flow cats.
At this point in time it is probably only 5 - 10 decibels louder than factory. And at high RPM's about 15 - 20 decibels louder.
Overall it still has the signature AM V12 sound, but more "emphasized". I have listened to the new vanquish, and I would say that my V12V is just slightly more aggressive (in sound) than the new vanquish.
I hope this helps anyone in the market for hi-flow cats.

 

Assuming my V12 would sound/react similar to yours, it helps a great deal! Thanks for the write up. Rep points for you my friend....

 

Appreciate the seat-of-the-pants opinion, but it'd be great to have actual data. If anyone else tries this, please do before and after dyno runs! I believe BR's cats only increased peak power by about 5 bhp.

 

I can afford the cats, sadly, not the car, at least not now.... trying hard though!
regarding DCBLS... 5 -10 is really a lot. Are you over stating that?

 

Great write-up. Hopefully you can take a video so we can really hear the sound..!

 

A friend of mine did before & after dynos on his DB9 and picked up 16BHP at the flywheel with exhaust/secondary cats/filters. I should grab them from him he has it all in a binder!!! I would expect the cats to account for 50-60% of that gain.

 

If these storms & the hail ever let up, I'll take a couple of quick videos to post.

 

I believe you are just becoming to the new sound level. There is not any system or process in which you car is adjusting for the new CATs as far as sound level. If you had a sound level meter readings I think it would validate this.

 

I suspect you are, at least to some degree, just becoming accustomed to the sound level as well. In addition, I would be surprised if your "butt dyno" could detect an increase of 5-8 bhp on a 510 bhp car. As I've said before, people's butt dynos are notoriously inaccurate. The increased sound provides an increased perception of power/speed that can convince the driver that more power increase has been achieved that has in actuality.

As I mentioned above, BR only reported a 5 bhp increase from cats. They ended up restoring the OEM cats on the customer's car because the noise levels were too high (the car also had free-flow manifolds) to live with considering how little additional power was achieved. From the PistonHeads discussion:

"The V12 Vantage was tested on dyno and at standard achieved 555NM @ 6000rpm and 507BHP @ 6900 rpm

The Bamford Rose V12V'S' exhaust manifolds and catalysts were added and achieved 590NM @ 6000rpm and 540BHP @ 6900 rpm

On top of the exhaust system upgrade Bamford Rose upgrade camshafts were installed and achieved 595NM @ 6000rpm and 565BHP @ 6900 rpm

On top of the exhaust and cam upgrade 200 cell density high flow secondary catalysts were installed and achieved 600NM @ 6000rpm and 570BHP @ 6900 rpm

This specification returned 112db static noise test at 5000 rpm exhaust valves open, 94db valves closed and 113db at a high engine speed / load drive-by which was a little too loud for Lance's pilot. So the decision was made to release the project with standard factory secondary catalysts where noise levels recorded were 102db static noise test at 5000 rpm exhaust valves open, 89db valves closed and 108db at a high engine speed / load drive-by, together with the deep baritone burble at idle and loud but not intrusive noise at high engine speed which maintained the almost V8 type growl, this was deemed "perfect" by Lance's happy pilot..!"

This is the type of actual data I would like to see before making any purchases. It's nice to have the dyno data plus actual decibel measurements.

 

Lol, well maybe his butt dyno is inaccurate, maybe it's not, but his built in db meter seems pretty good

Comment re: changing sound levels, cats do collect carbon deposits as they are used which decreases the heat they radiate and also should mute the sound levels somewhat.

 

Don't disagree that sound may be slightly less after a while, but not enough to make what you'd call a significant difference. I ran 200 cell cats on my V8V. They were loud when I put them on and still loud a year later when I took them off to sell the car.

 

The biggest problem on the V12s are the exhaust manifolds & primary cats, NOT the secondaries. On the V8 vantage, it's the exact opposite, MUCH better exhaust manifolds but highly restrictive primary/secondary cats. Hence why the V8 cats make significantly more power than the V12 ones because they are the primary bottleneck in the system. Whereas on the V12 is the exhaust manifolds. Each car requires a totally differen approach when modding the, and these factors should be taken into consideration.

On V12. The best route is to probably run the aftermarket V12 headers with stock secondaries and just relocate the 02 sensors to the secondaries (which at that point would basically become the primaries).

 

I'm just simply providing my perceptions, nothing more.
I don't have a db meter, garage dyno, or anything else.
If you guys want exact numbers, spend the money on parts & equipment and do it yourselves.
To myself, my family, and a few other hobbyists that know my car; it appears to have toned down a little since original installation. Maybe the ECM has adjusted the timing slightly or possibly the fuel parameters to accommodate for the increase in flow, or maybe my it's my selective hearing.
I'm not telling anyone to go do the mod or what parts to buy, or who to buy them from. I'm just telling you what I encountered (which I almost regret doing now).
I bought the cats for the increase in sound not for the power increase. Whether there is a power increase or not, thinking that there is one, helps to justify the costs.
I like the volume increase, some may not; it's personal preference.
I will be getting long tube headers soon, and that will be for the power.
At that time, I may also change out the hi-flow cats depending upon the volume.
The bottom line is the cats looked pretty, polished, & well built; but you can't see them unless you're underneath the car anyway.
The sound is perfect, but that's only my opinion; so it doesn't matter.
The car "feels" like it has more power, but it doesn't mean anything unless I waste money on dyno time to prove 5- 10 hp.
For the V12V dyno queens out there, maybe someone can prove some 1/4 mile times and track times. I don't recall seeing any hardcore V12V owners.
I might post some vids, but anything can be doctored with the internet.

 

So just because I'd like to see actual data on what the power increase is I'm a "dyno queen"? Sorry if you've taken offense, but you're the one who brought up power increase and many of us would potentially do this mod primarily for the power gains. In view of this, I think it's reasonable to want to see actually data (and no, I'm not saying you should provide it to us.).

 

Oh I agree with you, at least given my experiences with the cats on my V8 (and rep point to you for posting as well). The V8 is f******g loud just with cats and stock exhaust and my impression since I installed them a year ago is that they have quieted slightly. Certainly the quality of the sound has changed. It was startlingly brash and metallic at the time of the install, as if it was dining on scrap TVRs at WOT, but now ... hmmm ... approximates the purr of some feline Decepticon ...