[Erock78]

Hello,

I have a M5 CS with Akrapovic catback with Red Star secondary downpipes. I’m wanting to add Primary downpipes without tuning. I don’t want to do the DME Fetmo unlock and I’m hoping to avoid CEL. Has anybody here gone full catless without tune and use O2 sensor spacers to avoid the CEL? Thanks for any help with this! I love the sound currently but it’s still a little too tame compared to my previous E63s with full catless downpipes.

[pbonsalb]

Spacers won’t work. Spacers with mini cats probably won’t work. You won’t get that much out if the primaries without a tune to raise boost. Look up Velocity Tuning test of catted primaries versus catless. If money is no object, Fabspeed HJS high flow cat primaries or AA Gesi catted primaries would give a small gain. Buy a titanium valved cat back exhaust if you just want more sound.

[Erock78]

Thanks Pbonsalb. I do have an Akrapovic full titanium catback. I ordered the Red Star HJS primary downpipes. That should do the trick very well. According to Red Star customer service these flow 93% compared to full catless so they are almost as loud as catless while removing some rasp.

[Stlthnmrdrd]

Catless sounds good, but u lose low end torque and it's pretty noticeable. I recommend Redstar HJS. The 400cell gesi wont be much different in sound compared to stock downpipe, bc the OEM one is already highflow.

[Erock78]

Stlthnmrdrd The car in that video sounds killer!

[Info@mad-us.com]

Originally Posted by Stlthnmrdrd

Catless sounds good, but u lose low end torque and it's pretty noticeable. I recommend Redstar HJS. The 400cell gesi wont be much different in sound compared to stock downpipe, bc the OEM one is already highflow.

Agreed, the gains will be very minimal for the cost if you switch out the stock for a 400 cell.