R32 GTS (RB20DE) clogged cat

[GabsReDeal]

Hey everyone,

This is my first post apart of the introduction. I tried searching a bit on the forum but couldn't really get a straight answer.

I got the car to my mechanic as I felt it being weak. It seems that it was missing on two cylinders due to the injectors. I had all my injectors clean and the car runs much better. The mechanic also confirmed my suspicions that the cat is clogged and needs to be tackled asap. The cat rattles a bit and the hot exhaust warning frequently lights up when driving after getting the injectors clean.

In my introduction I was asked about what modification I might be interested in and mentioned a cat delete. From what I was told, this is not really beneficial on the RB20DE and there are more cons than pros. 

Could perhaps anyone give some suggestions on what the best course of action would be since the current cat is toast and needs to be removed/replaced anyway?
I can also sometimes smell a strong smell of fuel, but I'm not sure if this is related.

[Duncan]

I'm not sure what sort of shops are nearby, but I'd expect any reasonable exhaust shop could put a cat in it that will not restrict the power that engine makes.

Otherwise, if you want to remove it, short lengths that replace the cat are readily available online, search for "de-cat pipes" or "test pipes"

 

[MBS206]

The hot exhaust light will come on not from just the cat being blocked, but it's just a temp sensor, and it's designed to warn you to not do things like park in long grass.

 

If you've been pushing the motor a bit, it can cause the light to come on.

 

Second if the cat is rattling, I'd suspect it's not blocked, but instead falling apart inside.

 

The easiest "fix" until you can get a cat put back in, is to unbolt your one, bash the rest of the insides out, and then bolt it back in.

 

For a daily driver/street car, I am in agreeance of put a cat in the car.

If it were race car I wouldn't care if it were removed.

[Milkmun]

As above, definitely bash it or get it replaced with a high flow unit.

[GabsReDeal]

Appreciate the feedback. It is street car, but not a daily.

Last week I got a quote from a good exhaust shop for a decat, one which is bolt-on, bolt-off to be easily replaceable. I got quoted for around €150.

On 19/01/2025 at 3:42 AM, MBS206 said:

If you've been pushing the motor a bit, it can cause the light to come on.

I usually do push the motor, but I wasn't in this case to make sure that no damage is done until I get the cat sorted.

I think it's best to also ask the exhaust shop for the other option and see what they can do.

If (big if) I were to decat though, would it be best to tune the car or would the stock ECU handle it? As far as I know, the stock ECU is not tunable and that would require additional purchases.

[GTSBoy]

The stock ECU won't care.

The gains from Nistuning the ECU and then "optimising" the fuel and ignition tables will be about 2 more HP.

[joshuaho96]

10 hours ago, GabsReDeal said:

Appreciate the feedback. It is street car, but not a daily.

Last week I got a quote from a good exhaust shop for a decat, one which is bolt-on, bolt-off to be easily replaceable. I got quoted for around €150.

I usually do push the motor, but I wasn't in this case to make sure that no damage is done until I get the cat sorted.

I think it's best to also ask the exhaust shop for the other option and see what they can do.

If (big if) I were to decat though, would it be best to tune the car or would the stock ECU handle it? As far as I know, the stock ECU is not tunable and that would require additional purchases.

Stock ECU has compensation, you won't damage the engine. Personally I recommend getting an acceptable catalytic converter, it doesn't need to be OEM and super expensive but a cheap universal one to keep it from being super obnoxious to be around. Decatted cars smell pretty awful.

[PLYNX]

As above ! Cause I love the smell of sulphur dioxide in the morning !

[GTSBoy]

50 minutes ago, PLYNX said:

sulphur dioxide

Nah. H2S.

H2S is "rotten egg gas", which is what is associated with no cat.

SO2 is equally nasty, and if you've ever smelt it you'll know all about it. More of a choking, acid in the back of the throat sort of thing. But you can only smell it in a narrow range up to about 1ppm. Above that, it irritates your mucous membranes, but you don't smell it.

[PLYNX]

Oh bugger ! Your right ! Good old hydrogen sulfide.

Takes me back to the good old school days ! 

[niZmO_Man]

Should be able to source 200 cell R32 cat... unsure how easy it would be to get it to Malta though.

[GabsReDeal]

On 20/01/2025 at 11:37 AM, niZmO_Man said:

Should be able to source 200 cell R32 cat... unsure how easy it would be to get it to Malta though.

Yes shipping here can be a pain, was about to purchase timing belt replacement kit, but it tends to get expensive due to shipping (and customs if importing from non-EU which the UK now falls under).

[GabsReDeal]

Just a quick update: I decided to go ahead with the de-cat for now. The exhaust shop inspected the catalytic converter and said it was in good condition. I took a look myself, and it does not appear broken nor clogged.

After the de-cat, the car feels more responsive and smoother. The shop also reinstalled the exhaust temperature sensor into the de-cat pipe, and now the warning light no longer comes on, even when driving hard.

The only thing that’s bugging me is the tinny, “can-like” sound the exhaust makes now (similar to having a hole in the muffler). The shop suggested that I might need to replace the muffler.

I'll have to think on what to do next.

 

[niZmO_Man]

get a 200 cell cat

[GabsReDeal]

On 27/01/2025 at 2:06 PM, niZmO_Man said:

get a 200 cell cat

Will ask the exhaust shop about this and get a quote if possible. My current pipe is with flanges and not welded on, so I can easily switch to my old cat if I wanted. I'd do it that way too.

This shouldn't be an issue as long as there are no exhaust leaks afaik. Stock one was with flanges as well.

[GabsReDeal]

Small Update on the Exhaust Situation

A 200-cell cat was a bit too expensive for now, so I had the exhaust shop fabricate a new exhaust from the cat to the rear and an exhaust tip. I went this route to avoid cutting into the original exhaust and keep it intact.

It’s essentially straight-piped, and the sound is noticeably different. The exhaust tip came with a silencer, so if it gets too loud, I can easily install it to tone things down slightly. Right now, the car bangs and pops like crazy -- which I personally love.

In the future, I might add a resonator or a 200-cell cat, as niZmO_Man suggested, but for now, I’m really happy with how it turned out.

 

[niZmO_Man]

The Japanese ones are quite expensive, but aren't there any local generic ones that make 200+ cell cats? The should be like $200 (at least they were in Australia pre-inflation).

[GabsReDeal]

I was told that they no longer fit high flow cats over here for some weird reason. But one exhaust shop said that they may have some old stock which they could fit if I wanted.

However, I have other issues to handle at the moment and this is not a priority for now.