Been told if you want to live map your car to get a safe reading of afr you need to put a lambda sensor on the downpipe, is this true or can you use lambda in tailpipe?would the readings be any different??

 

It's better in the downpipe.. There's very little room for error then.

 

Agreed better in the downpipe, but when your car is setup on the RR they use a WB lambda that goes up your exhaust so either will be fine as long as its good quality!

 

Reading AFR from the tailpipe only really causes a problem a low speed because air may get into the exhaust and 'influence' the reading.

Also, any leaks in the exhaust will affect the reading too.

Theoretically, if the exhaust is 100% leak-free, then the difference between measuring from the tailpipe or downpipe is very marginal.