Hi over time my cats have disintegrated and Mot due soon (UK) so I have to fit some hi flow cats into my downpipes . Has anyone use anything specific or any decent 200 Cell will do ?
I know over in the UK that Vagtechnic has replaced the Cat core in the stock exhaust, they are in Dudley. Bad news is that you probably know that the engine has to be pulled to get to the Cats.
Doubling some other threads: I was wondering if these JHM JHM-RS5DPHFC Exhaust - 2.75" Performance High Flow Cat (HFC) Downpipes (JHM) for B8-B.5 RS4-RS5 4.2L HEADERS REQUIRED – ML Performance available from a store in the UK here: JHM JHM-RS5DPHFC Exhaust - 2.75" Performance High Flow Cat (HFC) Downpipes (JHM) for B8-B.5 RS4-RS5 4.2L HEADERS REQUIRED – ML Performance would fit OEM headers with gutted cats. Gutting them is at your own risk though, but that would be my first try. If they don’t fit, your headers would have to be sent to JHM and redone. An other member here mentioned it is a one of job for the remaining lifetime of the car and non OEM cats can be fitted in the same place.
I don’t know how strict the MOT is, but I think it is too strict for the following other option, I have mentioned in other threads, trying e85 risk of check engine light coming on if they fail it because of that , limit it to 45 % and try resetting CEL right before. It could work with 02 sensor spacers (This was done to remove CEL unrelated to E85 mixture but I assume worn catalytic converter successfully by another member here), so that the CEL does not come on, when running 100 % e85 (the car runs fine on it but consider the increased wear if run on it more often).
Some O2 spacers, I don’t remember if these fit the RS5 off the top of my head, but I think it is a standard diameter on O2 sensors. Akozon Oxygen Sensor Spacer, 2st M18 x 1.5 Universal O2 O2 Oxygen Sensor Spacer Adapter Extender Isolator
Yea, it’s getting to the point that JHM is offereing less for the B8/B8.5 RS5 than they previously had. Their website shows the Downpipes you listed with the H.F. cats require their headers, which have a slightly larger flange for a complete 2.75" flow. Their non-catted downpipes show that they will fit the stock header (rear of Cat). I’m pretty sure they use to sell the H.F. cat downpipe that bolted up to the stock header and I’d imagine they would still make it for you, they pretty much have do all of that stuff on made to order and don’t stock much. I had to wait for my 2.75" exhaust for almost 2mths while they did a run.
Not sure about your MOT, O2 sensor holes are a standard for pretty much all O2 sensors. Just depends on how long of an extender you purchase to whether it will fit in the space provided. I did the full JHM header and went completely Catless (it is a little loud as the Cats are a muffler too as a side effect of their restriction). I went with a custom version of their Stage 2 software that coded out the rear O2 sensors, and in my case, also coded out the SAI system as I removed both pumps and all of piping and hardware.
When I spoke to them they said I would have to have the headers to match ( This was last month ) so I guess they won’t build the ones to match the OE headers anymore then . I’ve been playing around with just V clamping in two decent branded Hi Flo Cats . It’s the only thing I can do other than throw thousands at it which ultimately both do the same thing . V clamped that way can do just on driveway . Compared to the later version B9 Unfortunately there’s not much available aftermarket
Yea, a custom job my be in your future. Stock Cats don’t last. I’ve seen people on here think they’re fine with 60~100k miles, just because of they don’t have a CEL. But I guarantee if they pulled the upstream O2 and inserted a video inspection camera they would see damage. The lucky ones are where the Cat breaks up into smaller pieces and travels down the exaust breaking up even further. The unlucky ones are where the Cat breaks into larger pieces and very shortly can plug the downpipe and cause a lean conditon due to backpressure and even cause valve damage.
Did you look into VagTechnic? What about Unit 20, Martin Adams (Grizz)? I know there are quite a few performance shops that deal with German cars, even Audi specific and or performance exhaust places. I’m sure you can call around and find a place that will do a custom install for a decent price.
For the hydrocarbons, as well, might be good to add some acetone which was used in the Silver Arrows: Exhaust emission reduction of a SI engine using acetone–gasoline fuel blends: Modeling, prediction, and whale optimization algorithm - ScienceDirect be very mindful and at your own risk though due to its strong solvent properties. I would go in with an empty tank mix say 5 liters petrol, add 1 liter of acetone and 3 liters of e85/ethanol mixed in a jerrycan then right after the MOT top up with petrol to dilute them more. If it is only HC exceeding I would go with only petrol and acetone and similarly if only CO, only e85 same as above ratios to the total or less if only a slight exceedance.