It’s hard to argue the fact most people will have some form of appreciation for an exotic car.  

See a Lamborghini Gallardo Spyder a Ferrari F430 or an Aston Martin DB9 and even a non-car enthusiast would likely take a second glance.    

Buying and driving a supercar however is not something within the budget of most. Enter Darren from XtremeX NZ. Darren gets you into the Supercar realm without dropping huge stacks of cash. Offering both ride and drive options from his fleet of exotics.  

Now focus your attention specifically on Aston Martins DB9. Affectionately known by most as the 007 Bond car. The DB9 is a 6.0 V12, a beautifully hand crafted masterpiece which dances between graceful and pure monster. Jeremy Clarkson has gone as far as calling it motoring perfection. It’s a British supercar and grand tourer wrapped into one. The v12 power-plant puts out ~450HP and reaches 100KPH in 4.6 seconds.  

From factory the exhaust note is good giving an inkling to what lies under the hood, but it does leave you wanting that little bit more. When your business model is offering people the true supercar experience, you don’t want just good, you need it to be amazing – Enter the Kaizen Works team.  

Darren came to us having done his homework, he’d found exhaust upgrades are readily available and performed on the DB9. His goal being to improve the acoustics, and enhance overrun to help add to the thrill of those riding in the car. Plenty of info of others who have modified their DB9’s was available and pointed Daren towards a Secondary cat delete incorporating a free-flowing x-pipe section. This modification replaces the restrictive factory secondary catalytic converters for increased exhaust flow and an improvement in exhaust tone. A whole litter of primary cats in the main headers still remains with one per 3-cylinders. The factory rear muffler box also remains untouched.  

This particular exhaust part was available in the aftermarket from overseas companies. However once you factor in freight, GST and fitting costs of imported exhaust components having a one-off item fabricated locally becomes competitive. It gives you a place to go back to for fine-tuning if it’s not what you wanted and you’re supporting local people to stay employed and support their families. Keep this in mind with any upgrades! 

Once Darren tasked us with this job we got the Aston into the Kaizen Works workshop and up on the hoist. One of the first things we did was create a new flange point so that options could easily be swapped between. The factory configuration didn’t allow for this so we installed a 2.5” v-band to each bank, just downstream of the secondary cats. 

We then flanged the factory cats so the car can be converted back to stock quickly and easily. Deleting cats can result in WOF failure so always check the rules around your specific vehicle. Keeping the option open to return to stock is nice, particularly for a vehicle like this. 

Now we had done this each of the 4 options we wanted to trial can be installed between the factory 3-bolt flange and new v-band flange points. We would test factory cats, straight de-cat pipes, de-cat x-pipe and h-pipes.  

All the options we fabricated are TIG welded stainless steel. This ensures a great looking product with better corrosion resistance over the mild steel alternative, something we always recommend.  

Now there is a lot of theory behind the differing setups and you need to examine how an internal combustion engine works to truly explain them but that’s a bit beyond the scope of this article! 

In short though, adding an H or X-pipe benefits V-configuration engines because they connect separate pipes coming from the two different exhaust banks. 

We would record DB readings in a variety of situations, being an external drive by, a launch and free rev for each of the 4 configurations. This would all be measured on our inexpensive DB meter that is nothing special but provides us back to back data.  

The results were a little surprising to all of us!  


As mentioned the stock note is really nice, no drone, and a subtle but menacing V12 growl under light load and acceleration. This note does disappear somewhat when you’re higher in the rev range and becomes a little lost. Expanding on the stock note by making it a little louder and across the rev range would be magic. No wonder Darren was after this. Stock averaged a 101.5db reading. 


Some feel X-pipes are better suited to free-revving overhead cam V engines, they are known for a more exotic type sound best associated with high revving exotics. By design they flow well allowing each exhaust bank to easily merge, equalize pulses and flow with one another. 

We were somewhat shocked at the overall noise reduction of the X-pipe. We expected an overall increase in noise through removing the restrictive cats but to find our DB readings the lowest out of all options, including stock was interesting. The DB reading averaged 96.5, a whole 5decibles quieter than the stock configuration. This wasn’t going to fly! 

The explanation? The great flowing nature of the X-pipe inherently evens out all exhaust pulses. The exhaust note did change to something higher pitched which was not very favourable amongst the owner or us. 


H-pipes are a natural fit for high-torque big-block V8 engines that make their power lower on the rpm scale. By design they somewhat fall over at higher RPM as the exhaust gasses take the path of least resistance – being the main exhaust pipes. 

The H-pipe provided the second best gain in noise improvement and was second on all of our lists also. It was on average only 1db louder than stock. It retained more of the factory noise but still did not really deliver the note desired for the true Aston experience. 

Straight de-cats:  

This setup least altered the factory exhaust dynamics as there were no major configuration changes at play other than simply removing the restriction of the secondary cats. The results backed this by an increased factory tone that now carried right through the rev range – we have ourselves a winner! A solid 4DB over the stock setup and a huge 9DB louder than the X-pipe! 

The factory rear box and primary cats were hard at work still maintaining no drone when coasting which was great. The nice growl under light load was still present and an enhanced aggressive bark when on the loud pedal now clawed its way out of the tail pipes..  

Check out Darren’s website for a range of affordable supercar experiences, whether for yourself or maybe a birthday present for another. He has options ranging from a 15min- 1hr experience both as a passenger, or a driver. 

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