Stainless steel tubular performance exhaust manifolds replace the standard cast iron manifold with a fabricated assembly of individual primary pipes merging into a single collector. This design dramatically improves exhaust gas flow compared to the restrictive internal passages of the cast iron original, where all four exhaust ports merge into a cramped common chamber before reaching the downpipe.
System Specification
Tubular manifolds are available for the 1098cc, 1275cc, and 1500cc engines. The stainless steel construction ensures the manifold will not corrode over its lifetime, unlike mild steel performance manifolds, which deliver the same flow improvement but will eventually rust through. The manifold includes the correct flange to mate with the existing exhaust system or a new stainless system.
Exhaust Fitting
When fitting a tubular manifold, the carburettor needles should be changed to a richer profile. The improved exhaust scavenging draws more mixture through the engine, and the standard needles will not provide sufficient fuel to maintain the correct air-fuel ratio at the increased airflow. Needle recommendations for manifold-and-system combinations are available. Exhaust manifold wrap can be applied to reduce underbonnet temperatures, the thinner-walled stainless tubes radiate considerably more heat into the engine bay than the thick cast iron original.