The outlets on my no-performance manifolds are maybe 1.750. The downpipes we whipped-up reused the first few inches of the factory pipes, which were something like 1.5 or 1.625, then stepped up to 2.0 followed by 2.25 and finally into the 2.5 system. It was one of those "raid the exhaust tubing at Autozone for elbows" deals. As bizarre as the description may read, it turned out very nicely. It works quite well, but will eventually make way for a set of Spitfires when cash flow allows.