D2a TD5 - modified exhaust system

[twr7cx]

What is the ideal size exhaust for the TD5 engine, particularly for an automatic model? At a guess I would assume 2.5" is a good size to maintain low rev torque.

What about the cat converter? Best replaced with a high flow unit or removed completely? Does removing it completely upset the ECU at all (I haven't look yet were the oxygen sensor is, but I know some vehicles with the oxygen sensor after the cat converter get upset if the cat converter is removed)?

[twr7cx]

For anyone interested. The answer from some of the tuners is that 2 1/2" is the optimal exhaust size. Which is a good thing for us owners as it means we don't actually have to change the exhaust pipe, but rather can just remove the restrictive mufflers and replace them with higher flowing ones.

"Why dont we make 'Big Bore' systems? A 3 inch bore system would not be appropriate for modern land rover diesels, since the turbo outlets are only 2 1/4 inches in diameter. Age old (Proven) tuning theory states that the optimal turbo down pipe should be 10% larger in diameter than the turbo outlet casting. This is precisely why land rover chose 2 1/2", as it's a perfect match to the turbo. Using 2 1/2" pipe maintains a rapid flow of exhaust gasses to get them out quickly! Using 3" pipe would reduce the velocity of exhaust gasses, their fore retaining excess heat at the turbo, and exhaust manifold. Another factor is the reduction of back pressure you'd get from a 3" exhaust, as the wide open space of the exhaust takes more gas to fill it, and hence push out the tailpipe. The result could potentially cause turbo over speed, which can seriously decrease the life span of your turbo."

Alive Tuning - Real Land Rover Performance for TDi, TD4, TD5, TD6, TDV6, TDV8, TDCi, Puma (http://www.td5alive.com/exhausts.php)