Will a 4-2-1 exhaust manifold worsen the performance of a Turbo engine?

Answer 1

This question is unanswerable without a wide array of specifics. It is unanswerable. In GENERAL. Regardless, you can expect a minor decrease in spool time, and a LARGE decrease across the rest of the powerband with a Log type manifold. From there a 4-2-1 will INCREASE the spool time a small amount and give somewhat more power. A 4-1 manifold will give the longest spool time of all (this is almost non-existant, but there) the three manifold types, and a LARGE increase in power avalible across the powerband. A classic modern example would be your typical 200hp, 8,000rpm shutoff small displacement Honda engine. It is widely proven and understood that swapping from a log manifold to a 4-1 manifold will increase the spool rate 200-400rpm, with a 30-40 horsepower gain any point afterwards. That is a VERY large difference in both peak power, and powerband. The same rules of thumb will apply to any other cylinder arrangement. If possible all cylinders should merge at the same collector IMMEDIATELY before the turbine entry. That being said there is a SERIOUS amount of turbulence when you try to merge more than 5 exhaust ports. That makes the lone contradiction to the "rule of them" in that a 6-2-1 manifold is always better than a 6-1 manifold. All things being equal. ANSWER it will make the "turbo lag" time longger