[Kanweezyyy]

Greetings everyone,

I've had my M5 for a few months now, I just recently picked up some primary and secondary catless downpipes. I got the downpipes through a friend although I'm still waiting for a few parts to show up but I'm a little tired of the stock sound. I wanted to throw on the downpipes but do I have to run a tune, will the car still run good without a tune? I do plan on tuning later down the road. Thanks !

[crypto]

Tune has nothing to do with whether or not you install down pipes. It's just to run more aggressive tunes out there, one of the modifications you would likely need is [catless] primary down pipes (with the secondaries).

[pbonsalb]

You will probably get a CEL that will make the car fail inspection in many states, but not all. Hopefully the OP lives in one that won’t be a problem.

[EM5C]

What has everyone's experience been on catless downpipes in terms of performance gain? How significant is the sound/drone compare to stock?

[pbonsalb]

Performance gains are limited because the stock cats are very high flowing. One member is trapping about 140 mph with stock primaries and catless secondaries. Obviously a custom tune and E30 and other mods, but very impressive.

On many cars the stock cats are so restrictive that going catless can yield huge gains. This has not proven to be the case with the F90. Carbahn claims the gains are so minimal it does not recommend catless. Others claim anywhere from 20-60 rwhp. Most stage 2 tunes recommend full catless though reportedly some tuners have said catless secondaries is enough (like HCP that did the custom tune on the near 140 mph car).

I’ll leave sound to someone else since I have not installed mine yet — this week. I bought CTS Turbo high flow primaries and catless secondaries as a compromise among power, sound and smell. They are priced well at about $1000 for the set. The MAD USA catless primaries and secondaries are priced well at about $700 for the set.

There is also smell, which bothers some and does not bother others.

[crypto]

Originally Posted by pbonsalb

Performance gains are limited because the stock cars are very high flowing. One member is trapping about 140 mph with stock primaries and catless secondaries. Obviously a custom tune and E30 and other mods, but very impressive.

On many cars the stock cats are so restrictive that going catless can yield huge gains. This has not proven to be the case with the F90. Carbahn claims the gains are so minimal it does not recommend catless. Others claim anywhere from 20-60 rwhp. Most stage 2 tunes recommend full catless though reportedly some tuners have said catless secondaries is enough (like HCP that did the custom tune on the near 140 mph car).

I'll leave sound to someone else since I have not installed mine yet — this week. I bought CTS Turbo high flow primaries and catless secondaries as a compromise among power, sound and smell. They are priced well at about $1000 for the set. The MAD USA catless primaries and secondaries are priced well at about $700 for the set.

There is also smell, which bothers some and does not bother others.

Interesting. I heard with the primaries you gain quite a bit in the sound department but I've never heard a catback exhaust only vs same exhaust with Down pipes done to compare.

Can you explain your comment about the compromise you mention where you added smell into the description? Do some catless primary downpipe solutions claim to result in less gas smell over others? How is that achieved? Thanks

[pbonsalb]

Keep one cat or use a high flow cat with the other pipe catless and there should be no smell. The smell of catless bothers some and others don’t even notice. Where you might notice is in stagnant air while idling. Sometimes a tune helps, if the car would otherwise run rich from the reduced backpressure of being catless, but these ECU are so capable that they may adapt enough after some miles that you smell less.

I went catless on my E90 M3 and the smell was so bad sitting in traffic that I got a catless tune right away. No issues after that.

[Camarejh]

I have catless downpipes with no tune. Check engine light is definitely on. As far as performance i dont really notice anything. Ill tune it when warranty expires. As far as sound?? Night and day. I have stock exhaust. The sound coming out of the exhaust is a tiny bit more aggressive but the main difference is the turbo spool. Car sounds like a jet engine rolling around the streets and sounds absolutely sublime to the point where i keep my stereo off while im driving around town so i can listen to it. Highway driving with windows up sounds stock. No drone. No difference unless you really punch it but still no drone. I love the sound so much that ill never add aftermarket exhaust. Hope this helps

[Ron1n]

Catless primaries will yield a CEL. Secondaries will not.

[SatinblkF90]

I heard power gains are to be had with only doing catless on the primaries, and none to be had on the secondaries (plus smell comes from doing secondaries but not primaries). The HCP car trapping 140mph with primaries still in place and recommending to do only secondaries seems to suggest the opposite is true, so not sure now.

[pbonsalb]

Leaving either cat will reduce or eliminate smell. Eliminating either cat will reduce backpressure and help flow. The primary cat is bigger and more restrictive than the secondary cat, but a flow bench test showed it was only about 5% more restrictive. Catless secondaries are more popular because they do not cause a CEL since the O2 sensors are before and after the primary cats and measure their efficiency, not the efficiency of the secondary cats.

[SatinblkF90]

Originally Posted by pbonsalb

Leaving either cat will reduce or eliminate smell. Eliminating either cat will reduce backpressure and help flow. The primary cat is bigger and more restrictive than the secondary cat, but a flow bench test showed it was only about 5% more restrictive. Catless secondaries are more popular because they do not cause a CEL since the O2 sensors are before and after the primary cats and measure their efficiency, not the efficiency of the secondary cats.

So maybe besides from flow differences, primaries yield more gains than secondaries because of the o2 sensors letting in more flow vs whats possible on secondaries?

OR

when tuned there is only a 5% difference resulting in similar gains between either option? (of course doing both will yield max gains)

[F90Alan]

Originally Posted by Camarejh

I have catless downpipes with no tune. Check engine light is definitely on. As far as performance i dont really notice anything. Ill tune it when warranty expires. As far as sound?? Night and day. I have stock exhaust. The sound coming out of the exhaust is a tiny bit more aggressive but the main difference is the turbo spool. Car sounds like a jet engine rolling around the streets and sounds absolutely sublime to the point where i keep my stereo off while im driving around town so i can listen to it. Highway driving with windows up sounds stock. No drone. No difference unless you really punch it but still no drone. I love the sound so much that ill never add aftermarket exhaust. Hope this helps

Have you done a resonator delete?

[pbonsalb]

Originally Posted by SatinblkF90

So maybe besides from flow differences, primaries yield more gains than secondaries because of the o2 sensors letting in more flow vs whats possible on secondaries?

OR

when tuned there is only a 5% difference resulting in similar gains between either option? (of course doing both will yield max gains)

No
Yes

[Info@mad-us.com]

It's hard to gain much horsepower without a tune because the car monitors the torque output. What ever power the downpipes make the car will compensate that with less boost to hit the stock torque limit.


Factory cars will run more boost on hot days and less on cold days for this same reason..

Originally Posted by pbonsalb

I’ll leave sound to someone else since I have not installed mine yet — this week. I bought CTS Turbo high flow primaries and catless secondaries as a compromise among power, sound and smell. They are priced well at about $1000 for the set. The MAD USA catless primaries and secondaries are priced well at about $700 for the set.

Our full set is below $599

[edwarjejeega]

Originally Posted by Camarejh

I have catless downpipes with no tune. Check engine light is definitely on. As far as performance i dont really notice anything. Ill tune it when warranty expires. As far as sound?? Night and day. I have stock exhaust. The sound coming out of the exhaust is a tiny bit more aggressive but the main difference is the turbo spool. Car sounds like a jet engine rolling around the streets and sounds absolutely sublime to the point where i keep my stereo off while im driving around town so i can listen to it. Highway driving with windows up sounds stock. No drone. No difference unless you really punch it but still no drone. I love the sound so much that ill never add aftermarket exhaust. Hope this helps

Is this with catless primaries and secondaries or just one of the two? Car runs good without a tune (regardless of the sensor CEL) and completely stock? No engine issues?

[Camarejh]

Originally Posted by edwarjejeega

Is this with catless primaries and secondaries or just one of the two? Car runs good without a tune (regardless of the sensor CEL) and completely stock? No engine issues?

I dont have the car anymore as i bought a G80 but the M5 ran amazing. Throttle response was super smooth. No engine issues at all. I had both primary and secondary catless. At first i went secondary catless only but honestly didnt notice a change in sound. So i got the primaries on and wow it was amazing. But you will get a CEL.

[edwarjejeega]

Originally Posted by Camarejh

I dont have the car anymore as i bought a G80 but the M5 ran amazing. Throttle response was super smooth. No engine issues at all. I had both primary and secondary catless. At first i went secondary catless only but honestly didnt notice a change in sound. So i got the primaries on and wow it was amazing. But you will get a CEL.

Thank you for the reply on this older thread. I was planning to just do secondary because I want to avoid the CEL on a stock car but I really want the turbo’s to be vicious. Probably going to do full Keller Downpipe set

[Camarejh]

Originally Posted by edwarjejeega

Thank you for the reply on this older thread. I was planning to just do secondary because I want to avoid the CEL on a stock car but I really want the turbo’s to be vicious. Probably going to do full Keller Downpipe set

I had the same mindset as you. I hate check engine lights. It drives me crazy so i went with secondaries first and i was extremely disappointed. Turbos are def vicious with the full set. Tons of turbo spool up front even under light throttle and alot of turbo sounds out of the exhaust and i still had the stock box and resonators. If youre curious on the sound shoot me a txt and ill send you a couple videos of my car. 6192091318

[pbonsalb]

Originally Posted by edwarjejeega

Probably going to do full Keller Downpipe set

That is one way to spend $2000 more than necessary.

[edwarjejeega]

Originally Posted by pbonsalb

That is one way to spend $2000 more than necessary.

In terms of primary/secondary together or just Keller as a brand?
I’ve heard a lot about ER and it’s definitely a great alternative as it’s half the price, but I’ve also heard Keller is a perfect (100%) fit whereas some shops have trouble getting the fitment on ER.

[pbonsalb]

I don’t doubt Keller is high quality, but these are all stainless downpipes that have been installed many times without issue. MAD is the best deal on downpipes. I have installed those myself.