[gaza01]

So my biggest let dowon on my 325i is the engine sound! Its ridiculously silent in stock mode. Ive got a PE back box that has helped loads but still not the sound im after so changing the down pipes is an idea ive been touing with.

Getting after market downpipes for a 325i is difficult i found so i thought of getting stock ones and cutting the cats out! What do you think? I been offered stock dps for £250.
Ive heard once the car is warm it will pass MOT emissions without these cats in?
Anybody done aftermarket dps on a 325i or any petrol? What gains benefits did you get?

[doughboy]

Which engine variant is yours exactly - then you can check the diagrams to se your cat layout.

If it has separate primary and secondary cats (like a 335i) then you can remove the primaries for power and will pass and MOT on the secondaries.

But I don't think it would work the other way round as the secondary cats are bigger.

Primaries don't make much noise difference, there removal on a 335i is to aid turbo efficiency.

The thing with noisy exhausts is its mainly other people who can hear it, not the driver.

Whereas induction noise is a) nicer b) more discreet c) audible to driver too.

As your's is a NA motor, it should be ripe for a nice resonant induction kit?

[gaza01]

Its a N53 and it has both primary and secondary cats.
I thought most guys who had dps installed said they got a better sound?

[doughboy]

But on the 335i/N54 the primary CAT is a post-turbo CAT, and the noise change is very different to a N/A car.

Also, most of the noise change is due to the aftermarket Decat DPs being made of very thin walled stainless steel so it adds a metallic rasp from the DPs which you would never get by chopping up standard ones.

Also you'd have all the problems with emissions fail warning light and codes etc. The products for defeating these are aimed at the N54 / MSD80 DME only.

And the front CATs on your N53 are MASSIVE compared to the the N54 ones, so it might well fail the MOT without them

I think your straying into unproven ground here....

[gaza01]

Ah i get ya!
Its defo unproven ground hence me asking. Yr right on all accounts. Those primary cats on the N53 are HUGE!!! I'm just chasing a deeper rumble more than rasp but if its gonna throw codes and cause issues then im not going to bother. If it was something i could do myself then i would have given it a go but no point spending on the cats and then labour to put it in only to realise it doesnt work well and have to spend more money to take them out!
Thanks for yr help!

[zltm089]

Maybe look at induction kits?

Downpipes are a pain in the ass to fit on a 335i, not sure about the 325i. Being NA, I assume an induction kit would give some lovely music out!

[gaza01]

Got any links to good induction kits?

[Bee Pee]

Be warned that new MOT regs require cats to be visually checked these days. If tester can't see what looks like cat, a cat less exhaust may fail MOT, regardless of passing emissions.

[zltm089]

Originally Posted by gaza01

Got any links to good induction kits?

They're quite popular in the states...

http://afepower.com/shop/details_new...BB1&brandID=53