I would recommend the cat personally as it will help more with the smell than not having it - Rawtek Performance in Canada actually prides themselves on sourcing a catalyst in their TDI systems that takes care of 95% of the smell :) - I actually am going to email them to see if they are developing something for the 335D/35D

Would almost be best of both worlds to delete DPF and EGR to open up the engine breathing yet retain SCR/urea injection to take care of the smell/NO
- I wonder why that hasn't been done before, I guess because people don't want to be bothered with piss injection -

I'll second that.

DEF is cheap. I've got no problems topping that up, assuming SCR functionality can be maintained while deleting the DPF and re-circulation of exhaust gas though my engine. At the end of the day, I'm not trying to be green, but if I could curb some of the output while opening up the performance and longevity...it would feel like a happy compromise.

I would guess NoX sensors would get fouled pretty quick with DPF absent.
Unless, the solution is to ignore NoX sensors and just pump urea at constant rate (or based on RPM).

I'll mention.....

There is some benefit of keeping the DOC. The Diesel Oxidation Catalyst (DOC) not only reduces Carbon Monoxide (CO), but also unburned hydrocarbons and organic soot. So without it is much like running a car hatless and will result in more diesel stink. Its the unburned HC that makes diesel stink.

There are downpipes that remove the DPF but include a DOC to reduce the stink. North American 335d Post DPF Removal Exhaust Ideas - Page 9

Typically your SCR won't last long with a DPF delete. The SCR isn't designed to handle all the soot that passes through the system when you remove the DPF and clogs up after a few K miles. ABC delete without gutting SCR

In this case delete the DPF and SCR together or neither, its easier on an X5 than it is on a 335d. The only one that can be done independently is the EGR delete.

Well, deleting the EGR will result in a clogged DPF very soon. As you say it is all or nothing.
The emission stuff is there for a reason, not only user headache. The fact is, once the emission stuff gets deleted the car will stink and smoke and there is no way around it. Could be more, could be less, but it will be nothing like an original car.
I miss my clean car in a way, but everytime i step on the gas the regrets are gone with the smoke in the mirror :D

Some things maybe different between tuners. I'm aware that both BPC and JR Tuning offer EGR delete with the rest of the emissions systems active (DOC/DPF/SCR in place and on). I personally have such a tune, and they offer multiple EGR options including, a full EGR tune out, or a partial so that the EGR is only active during cold starts and or during DPF regens (not required, but improves fuel efficiency). EGR partially or fully disabled opinion?

Also Lots of folks run EGR blocks with no tunes and have done so successfully for > 60K miles. Hooper on the 335d forums blocked his EGR with no software tune for for more than 60K miles and the car functioned normally (other than an SES every 2nd start until it was erased) Those with the blocked EGR

The X5 does have 2 EGR paths unlike the 335d which makes things a bit more complicated to block.

I'm running a JR Stage 2 Tune with EGR delete and have not had an issue with my DPF becoming sooted up, it still does normal regens, been very happy with the tune.

T

Now this makes much more sense - and I agree that the SCR catalyst would get clogged up quick without a DPF in place - although my point was just a constant dosing rate of urea in order to keep the NO down, although you'd still be letting soot past -

Either way, I would DEFINITELY do the diesel catalyst to cut the stink down - Andrew @ FixmyVW has a nice EGR/DPF delete and includes a catalyst and EGR block off for about $1000 - just add a tune and your axle back exhaust of choice if you so choose -

BMW X5D DPF and SCR cat delete - 3"

Dosing urea and not having DPF filter in place is a bad idea. The surface of SCR cat will get fouled and clogged very fast not to mention carbon buildup on NOX sensors. The complete EGR DPF SCR delete package is a must for that reason. I have some old diesels that do not have DPF EGR and SCR not even CAT installed coming to my shop all the time and if everything is OK with the engine, injectors, air induction etc there is almost no exhaust smell at all. They puff a little cloud of smoke every now and then when floored but smell is almost absent ...or I may be just used to it being a diesel tech.

I just got an email back from Rawtek Performance in Canada as well yesterday - he told me they are working on a 335D solution now and they are hopefully going to be able to offer a 35D package in the coming months! So stay tuned - nice to have more options for our 35D's :)