Exhaust and lambda sensor question

[sniff diesel]

I've got a 1992 BMW 325i E36, with the M50B25 non vanos engine. I'm wanting to fit this nice set of used M3 S50M30 exhaust manifolds:



As you can see they're a lot better than the standard restrictive original cast iron manifold:



They bolt straight on to the M50 head, but the only trouble with that I can see is that there are 2 lambda sensors on the M3 setup as it's separate all the way through:



Whereas the 325i one joins into one for the single lambda sensor:



I'm not sure weather it'll run ok with the one hole blanked off with a plug, or if the ECU will then only detect the emissions from 3 cylinders and mess things up. Other option might be to splice the wires from a second lambda sensor into the original one to send a signal from both pipes to the ECU. Can anyone shed any light into this?

Edited by sniff diesel on Wednesday 22 July 19:15

[stevieturbo]

It'll work just fine on 3.

The cast manifolds dont look that bad.

[sniff diesel]

stevieturbo said:

It'll work just fine on 3.

The cast manifolds dont look that bad.

Thanks for that Steve, I think I'll give it a go with one blanked off then.

TBH the cast manifolds are quite thick so the inside is quite restricted, I've heard the M3 exhaust conversion is worth about 10-12bhp,

[Marquis_Rex]

sniff diesel said:

stevieturbo said:

It'll work just fine on 3.

The cast manifolds dont look that bad.

Thanks for that Steve, I think I'll give it a go with one blanked off then.

TBH the cast manifolds are quite thick so the inside is quite restricted, I've heard the M3 exhaust conversion is worth about 10-12bhp,

The M3 exhaust manifold is definately worth having. I'm suprised they bolt straight up. I would forget quotes of 10-12 Bhp. Thats just pub talk crap:It's very unlikely they would tune at that 325i 5900 rpm peak power engine speed to suddenly give that boost in power there and then. People need to stop thinking so much in terms of peak numbers. The benefits these manifolds offer are alot of bottom end torque on cars with variable cam phasing-where there's alot of overlap at low rpm. On fixed timing engines they'll offer benefits probably at various parts of the rev range, bolstering up the torque curve although there is likely to be an area where the torque is slightly worse- due to adverse anti-tuning (variable cam phasing cars can get around this using their VVT). They offer less restriction which is of some benefit (slight)-combined with the tuning benefits it's all definately worth having!