I agree, boosted z. Log manifolds are not the best for flow. You do want to keep heat in the turbine housing, but a simple coating or exhaust wrap can do that for you. A tubular manifold will scavenge exhaust gases much easier from the heads. Log manifolds are easier to produce (most bolt on kits use cast iron), and it's easier for them to retain stock parts like ac/power steering and stock downpipe locations rather than building a top mount manifold. I wouldn't say that top mounts are all form, they do make good top end power and high dyno sheets from what I've come across.
Switching from a log manifold to a tubular mini ramhorn, I saw the same power levels at lower boost pressures on my other car. Just my opinion
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