jmartpr

So the OAP not only have the GPF but also a second cat? What a way to choke this engine......

TDT

Guess it was necessary to split cats into 2 parts to meet the emissions targets within the thermal and packaging constraints. The big boy engine pushes more air faster than casual 4.0 so needs space and volume to get it out effectively.

992 GT3 + 3RS just has bigger cat units and then OPF filter directly after it in one combined unit.

jmartpr

But the secondary o2 sensor for cat efficiency is between the 2 cats....so if you want to properly measure cat efficiency it would be after the second cat.

TDT

Well it’s possible that someone somewhere is wrong then….

shawfm

Or they tossed the extra stuff on to choke the engine just that little bit from the GT3 & 3RS

UncleDude

Has anyone tried to hack the stock back box and somehow blend the banks? That might be the last frontier!

Avera

Yep . . . which is why, like the GT4, the best aftermarket tune for the RS will probably be Dundon headers/OAPs. Once Dundon dumps two (of four) cats and the GPF the gains should be epic (not that the GT4 needs more TQ/HP).

To boot, the decibels out the exhaust tips will amped up, again, probably even more than Dundon achieved with the GT4.

The cabin acoustics of the RS are already epic.

I suspect we will hear all the same stories about trying to cross a bridge too far . . . where enthusiasts like me tried to get a rear box solution to match up with the Dundon headers/OAPs, only to find mind-boggling drone is the price for improved tone.

Headers/OAPs with OEM rear box is most likely going to be the best solution available. . . if one is committed to Dundon.

Avera

Knutsm01

Does does the OAP need to have a cat to not throw a CEL?

usctrojanGT3

Wait, the GT4RS as 2 sets of cats and a set of OAPs? Didn't the GT4 only have just 1 set of cats a set of OAPs? I want to remove that butt plug of the cat/OAP going to the rear muffler and some good flowing headers. Those 2 things will improve the sound and give the car a bit more power.

BabyNSX

It seems to me that this may be one of the key reasons the GT4rs is down on power vs the GT3... they inserted another cork in the exhaust.

jmartpr

No...the secondary O2 sensor is after the primary cat in the manifold but before the supposedly secondary cat/GPF section.....so this last section is not monitored in US Spec cars.

jmartpr

Plus smaller diameter on the muffler internals compared to 992 GT3

jmartpr

That's what Dundon said on their Instagram video.....when you see the OAP up close on the video it looks like this could actually be true, It looks like it has two sections. There's your missing 10 hp.

TDT

Have we seen this detailed/confirmed?
The dundon video didn’t say this and I haven’t seen any information that 4RS has different set up for various markets?
If you have could you give a pointer or maybe someone can confirm sensor locations on their cars.

992 RS has been adapted since 992 GT3 with larger car and smaller OPF matrix and doesn’t use temps sensors anymore, instead taking that data from the map.

Maybe we discover that 4RS is adapted in the same way and monitors via map rather than sensor reading?

jmartpr

Here's a official PAG parts diagram...check out part #25, that's the secondary O2 sensor right before the GPF section. Pretty similar to Dundon's setup on the GT4 and what the Clubsports use.