DavidL wrote:Is there not a greater risk of cracking with a stainless steel manifold, or is that an old wives' tale?
Yes, but it depends upon the design. Stainless steel is more brittle than mild steel, that means it is more likely to crack if the exhaust bottoms out. However, any exhaust that persistently hits the ground is going to fail eventually, so a manifold and exhaust that fits up snuggly close to the subframe and in the tunnel is better, whatever material is used. The other potential cause of cracking is due to differential expansion. Stainless expands more than cast iron, at around 10m/m°C x 10^-6 in the operating temperature range of an exhaust, the figure for mild steel is around seven, whilst for the cast iron of the block the figure is around six. However, on something like an LCB, where you have two long outer branches the expansion isn't a problem as there is plenty of length of tube to accommodate flexing. If the two outer pipes were short and met the centre one almost level with the ports, which you might do with an exhaust manifold for a turbo engine, then using stainless steel could be a problem.