i have just bought a 2.0l to go into my fiesta and i have a four branch that will fit, will i need to put the o2 sensor into the exhaust in order to make it run right and get a half decent fuel economy out of it? i also have a stainless full sytem about 2.2 inch i know that will probably affect it what has everyone else done?

Thanks

Alight mate, yea, he lambda sensor/o2 sensor needs to go in the downpipe.
The exhaust will have some affect, but 2.2" might be a bit big and cause too much of a loose of backpressure.

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you will need the lambda sensor if running the standard management as closed loop, if mild steel manifold just weld in the standard position a boss as below for £3 and drill hole to suit.

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Will