Catless Down Pipes

[Toneaero]

Has anybody only done a catless downpipe WITHOUT upgrading the full exhaust system?

I've only been able to find posts on full system upgrades but im interested in doing this in 2 stages. I want to first change out my downpipes, then go with a full akra exhaust system.

Does anybody have experience with this? Does catless downpipes with stock exhaust sound funny?

[Brian425]

I am waiting on a set of AR Design catted downpipes. I hope to have them this week. I plan on running them with the stock exhaust. From talking with various vendors, and BMW tuners, I don't think you will be giving up much HP using the stock exhaust with the DPs. Even the best exhausts are only giving weight savings and +10hp.


I would expect the exhaust note to be a little louder and the turbo noise a little more obvious (more so with catless). I am curious why you chose catless DP? Are you going to get a custom tune to turn off the check engine light, or will you try spacers on the O2 sensors?

CEL's annoy me to no end, so I went with the catted DPs. I know I left a few HP on the table; but, I was dead set against risking an ongoing CEL issue.

I have Dinan's stage 2 tune and expect to add intercoolers and their stage 4 tune by year end. (Just waiting for their next 15% off sale.)

[Toneaero]

I decided on catless DPs for two reasons.

1. Louder exhaust
2. 70+hp at crank (claimed)

From numerous reviews on people upgrading their exhaust systems, especially the akra, complained that it marginally increased the decibels. The decibels increase significantly when catless downpipes are also installed. Therefore, the OE cats in the DP are very restrictive.

I do know that I will need to update my tune from Velos designwerks with a catless downpipe version but im not 100% if that will clear the CEL. I'll send Omar a note and see.

[Brian425]

I've heard alot of good things about Omar. You should be in good hands.

One thing to ask. In some cases, to turn off the CEL, the tuners leave the O2 sensor in a not fully ready state to avoid the cat efficiency below threshold code. If you state does their emissions testing based on OBDII, you may fail due to a failed OBDII readiness test.

There are ways around this. For other vehicles, there are true O2 emulators that will mimic the signal of the O2 sensor. You can also drill out sparkplug antifoulers and try varying spacers to fool the computer to thinking that it is seeing the data is wants. (You can measure the volts on the O2 sensor and see what brings you closest to .45v. O2 sensors will read from .1v to.9v, .45v is about 14.7-1 air/fuel ratio.) You may need to play with the O2 sensors before and after where the cat was to get a similar reading. I would be willing to bet that if they are far our of range of each other, you will get a code.

My experience is with older DSM cars, mitsubishi starions, some subarus, and mustangs. I have very little BMW specific knowledge. I am learning.

Omar will definitely know better. You want to make sure that you clear the CEL in a way that allows you to pass emissions. Taking out the DP's is only a 3-4 hr job, so it is not unreasonable to do it each year for emissions.

Also, before you order. Be aware that at some point, BMW changed from a flanged connection on the DP (shown in your picture above) to a slip fit connector. Be sure to go under the truck and confirm what type you have before ordering.

[Toneaero]

Lucky for me, MN doesn't have emissions testing since 1999.

Good call on the flange vs slip fit. I will have to check underneath before ordering DP. I'm 80% sure my 2010 is flanged but I will visually check.

The instructions found on akra's website looks pretty straight forward on DP removal and installation. I can't imagine it taking more than 2 hours to do. But...with my luck with working on cars, its going to take me 8 hours because ill end up stripping the head on one of the bolts....

[Mr.X5_3.0si-retired]

thought i'd bring this back as my city just got rid of emissions and i wanna run catless now..
i'm guessing like cold air intakes there's also no performance headers for the x5 either..
i've got an '07 3.0Si and checking your above 'akra' DP mentions they all seem to be for X5M's, anyone know if there's any non M e70 catless DP's or any other way i can run catless otherwise?

[Sylvan Lake V35]

Originally Posted by Mr.X5_3.0si

thought i'd bring this back as my city just got rid of emissions and i wanna run catless now..
i'm guessing like cold air intakes there's also no performance headers for the x5 either..
i've got an '07 3.0Si and checking your above 'akra' DP mentions they all seem to be for X5M's, anyone know if there's any non M e70 catless DP's or any other way i can run catless otherwise?

You could gut the cats out of your OEM pipes. I did that with mine, you will also need away to turn off the CEL mine required a tune to achieve that.

[Mr.X5_3.0si-retired]

Originally Posted by Sylvan Lake V35

You could gut the cats out of your OEM pipes. I did that with mine, you will also need away to turn off the CEL mine required a tune to achieve that.

i was asking around locally and a lot of ppl were mentioning to hollow (gut) it out too.. do they have an o2 simulator for these like i've seen in the past for E46's or could i even relocate my o2 sensor, i just had them all replaced so it would be nice to still use them if possible