On P1. Doesnt happen all the time, but occasionally hear a 'popping' noise coming from the rear of the car when heavily decelerating and only happens when changing down to 2nd gear! Any ideas??

I have a P1 with prodrive back box and scorpion de-cat centre.My car pops all the time when engine braking in third and second gear at around 3,000 rpm.I think it is to do with the higher boost than a normal turbo plus a bit of fuel being forced through
marty

Cheers Marty. I have Scoobysport backbox only on mine. Does it happen all the time on yours or only now and again?

What exhaust have you got ?
Unburnt fuel goes into the exhaust on the over run then you back off after accelerating, when the exhaust it hot the fuel burns in the exhaust causing the popping noise.
Its usualy on full decat exhausts as there is nothing to stop the gases, adding a vent to atmos dump valve can also help along with a decat as the dump valve can cause the car to run a bit ritch.
if youve got a full decat when you hear the popping people behind you may see flames come out of the exhaust :)

Andy

Hi Andy. The car is running standard down and centre pipes with SS backbox - can you still get the fuel burning in the exhaust in a non decat?

Yep

But it helps if there isn't a turbo in the way ;)

MY97 Sport with SS BB, full set of cats :D