Should I decat, any suggestions?

[stokiedundee]

Hi my fellow zoners. I have a 1990 316i manual E30 5 door, and what I want to get done is a decat, but I dont know if its worth doing. The only reason I want to do this, is to get a slight increase in performance. I have already replaced my stock back box with a cherry bomb as they sound nice/look good on old classics. I gained abit more performance. And I've replaced the stock air filter with a k&n filter. I know the 316i is known to be slow but I just want to get abit more performance without spending daft money as I only paid £400 for her a month ago. Any advice/suggestions guys? Thanks for reading (sorry for mini essay!)

[Nobby_N]

Do they have a Cat?

[Grrrmachine]

Unfortunately the M40 engine you have doesn't mod well. And if the new filter you've put on is a cone filter, you'll have made things worse, not better (panel filters are alright).

There is a loophole regarding when you HAVE to have a cat on your car (BrianMoooore knows the specifics on this), and removing it might yield one or two horsepower more out of your engine. But there really isn't any point throwing money at an M40; if you want more oomph, save up and drop a twin-cam M42 in there.

[verde]

I dont recommend doing it but if you so decide then I have a mid sectoin DECAT pipe il sell you.

[Brianmoooore]

The cat. on a M40B16 robs the engine of about 2 bhp, which is unnoticeable in the real world. It has a much more detrimental effect on fuel consumption, however, so I'd remove it for that reason alone.
I'd recommend replacing it with a genuine non cat. front section, though, rather than a straight piece of pipe.

[stokiedundee]

Unfortunately the M40 engine you have doesn't mod well. And if the new filter you've put on is a cone filter, you'll have made things worse, not better (panel filters are alright).

There is a loophole regarding when you HAVE to have a cat on your car (BrianMoooore knows the specifics on this), and removing it might yield one or two horsepower more out of your engine. But there really isn't any point throwing money at an M40; if you want more oomph, save up and drop a twin-cam M42 in there.

Thanks for your advice mate and its a panel filter, I'm not a fan of the cone filters. I'll have a word with BrianMoooore.

[stokiedundee]

The cat. on a M40B16 robs the engine of about 2 bhp, which is unnoticeable in the real world. It has a much more detrimental effect on fuel consumption, however, so I'd remove it for that reason alone.
I'd recommend replacing it with a genuine non cat. front section, though, rather than a straight piece of pipe.

Thanks mate, can I get 1 off ebay if there aint 1 on here for sale? And how many mpg do u think I'll achieve once its off? At the moment I achieve 35 - 40mpg around town and 45 - 50mpg on a motorway run.

[stokiedundee]

Do they have a Cat?

yeah mate.

[Brianmoooore]

Should be worth 2 - 4 MPG, by BMW's own figures.
Should be plenty of front exhaust sections available on here from our trusted traders.
Note that there's a bit of other work to do if you remove the lambda sensor as well as the cat.
Your air meter (AFM) should have an adjustment on the side of it, which may have a red plug covering it. This potentiometer is currently disconnected and unused, but if you remove the lambda sensor there is a plug and socket, connected to grey/black wires, situated under the bulkhead wiring cover at the rear of the engine compartment, which are both hanging free at the moment, but need to be plugged together to connect the potentiometer to the engine ECU. The idle CO level will then need to be adjusted by turning this pot, since it will no longer be controlled by lambda sensor feedback.

[stokiedundee]

Thanks mate, I may just leave doing it for a while or may just leave altogether because it does'nt seem worth it for the mph or mpg I would gain. Thanks for your advice thought mate.

[broadie]

Once the cat is removed is there much of a gain to be had from the lambda sensor removal ?