Put my car in the garage today to have the centre pipe of the exhaust changed from 50 to 60mm on my 99 2.2 Vti Prelude.

On checking the downpipes on the manifold they measured 45mm going into a 57mm collector which then went down to 53mm just before the flexi.

I was absolutely gobsmacked when they rang me to say that the collector was only 42mm. When I saw the collector pipe they removed it was 2x45mm into a 42mm, the 57mm was just a sleeve over the top of it. Surely this would be a bottle neck, why did Honda sleeve it down to 42mm.

They have now cut the exhaust back to the bottom of the downpipes and fitted a 2x45mm into 60mm branch and then 60mm right through to the 2x45mm rear pipes.

Just had a short drive home and it's damp and slippery so didn't want to push it but initial reaction is that midrange torque isn't much different and top end seems to rev more freely. I was getting a drone/vibration around the cabin at midrange and while it hasn't gone completely it is certainly more bearable as the exhaust note is a bit deeper.

It's going back on the RR in about 12 days time so that will be the real test. Maybe there is a placebo effect but the car does seem more responsive, freer revving and the engine seems a bit smoother. I'm well happy with the results.