Caterham 7 420R Decat Install

Updated: Oct 11

The removal of the catalytic converter is a popular modification and one which has been on my to-do list for some time. The general consensus is such that the catalytic converter gets a hard time with the standard Caterham engine map on the Duratec models. The noticeable pops and crackles produced through the exhaust with the standard map can cause damage to the expensive catalytic converter, thus it's better to replace with a de-cat pipe and save the catalytic converter for MOT time. A de-cat pipe can also improve engine performance through improved exhaust gas flow. Though without any hard data that can be debatable. There's certainly an argument to suggest the exhaust note will improve as it will reduce the muffling effect caused by the internals of the converter.


During last week I'd received a genuine Caterham Cars de-cat pipe or collector, and so this weekend was all about the install.


The link below is for the Caterham Cars 420R De-cat pipe.

https://caterhamparts.co.uk/collectors-catalysts/7151-polished-collector-french-duratec.html


The removal of the catalytic converter and installation of the de-cat pipe (collector) is a conceptually simple task. There are a few fittings but nothing complex, that said I'd organised some help before starting, my mate Mark. Why? An extra pair of hands to pull and push. After approximately 3500 miles and 18 months, I figured the exhaust components might be reluctant to separate.


I'm not going to turn this blog post into a hugely detailed affair, as I mentioned above it's a pretty straightforward process. That said, there are a couple of tricks which made the process easier, and I think it's worth covering those.


First up we slackened off the retaining bolt on the lambda sensor, a 22mm spanner is required for that. Next, we slackened off the worm drives retaining the catalytic converter heat shield. Followed by the nuts and washers holding the silencer to the rear exhaust bobbin. Finally, the exhaust clamp between the silence and cat was slackened and pushed forward out of the way.


At this point, we used a craft style (small) heat gun and applied moderate heat to the outside of the joint between the silencer and cat. A liberal amount of WD40 was then sprayed into the joint. The WD40 was left for around 10 minutes to penetrate, we then pulled the silencer back off the rear of the catalytic converter. Even with the use of WD40, the two were mated pretty tightly, however with plenty of pulling and twisting they eventually separated. Once the silencer was removed the heat shield and exhaust clamp could also be removed.

Silencer disconnected from the catalytic converter

We then immediately sprayed WD40 onto the joints between the catalytic converter and 4 downpipes, giving it maximum time to penetration.

WD40 penetrating fluid to help ease the components free

This next bit was initially perceived as likely to be the most tricky. Removal of the two retaining springs between the cat and downpipes. It wasn't difficult, in fact surprisingly easy. We used the same technique I'd used during the install, that being to compress the spring and thus release the tension from the wire retaining loops with large cable ties. We inserted two large cable ties through each spring, contracted each cable tie, compressing each spring. The top spring was removed with ease once compressed. The bottom one required slightly more persuasion using an extra cable tie to pull across on and slip over the hook. Ultimately both were off in under 15 minutes. We kept the springs compressed with the cable ties, ready for refitment.


At this point, the catalytic converter was pulled free from the downpipes with relative ease. Early in the process, we'd decided to leave the lambda sensor in place. Why? Having slacked the retaining nut off we didn't want to remove the sensor by twisting the sensor cable and possibly damaging it. Nor did we want to unclip the sensor from the harness and all the wiring under the 420R chassis. Our approach was to unwind the catalytic converter off the lambda sensor threads and thus remove the sensor from the cat. Doing so would mean the cable wouldn't twist and could remain in place. Since I'd raised and place the 420R on dollies there was just enough room to spin the cat under the car and remove the sensor. This approach worked a treat, avoiding a lot of hassle. I'd strongly recommend lifting your car and doing the same.


With the catalytic converter and lambda sensor now removed it's basically the same process but in reverse, using the new de-cat collector. This includes spinning the de-cat pipe onto the threads of the sensor, using the compressed springs and so forth. Our reassembly steps didn't take long at all.

Cable used again to compress the retaining spring clamps

We used WD40 on all mating surfaces which allowed everything to slip back together with ease. Aligning the 4 downpipes can be tricky, but again the extra pair of hands came in really useful.

Caterham Decat collector fitted

Before fitting the de-cat, we weighed both the catalytic converter and de-cat pipe. There was quite a difference, so much so we needed different scales as the de-cat wouldn't register on the bathroom scales used to weigh the catalytic converter.


The weights are as follows;

- Catalytic Converter = 2.9 kg

- De-cat Collector = 1.3 kg


Saving of 1.6 kg isn't bad.


Sadly the weather so far this weekend has been terrible, so no road test as yet. As soon as I can get out in the dry I'll follow up with some comments regarding how the Caterham 7 420R sounds with the de-cat.


As always you can find additional photos on my Instagram.


Thanks for reading, and as always stay safe!


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Meet Mark
Loves cars, light weight specials, jDM, Lotus, Caterham, Rallying and Trackdays