Ages ago when I first looked into building a turbo application, the common theory was the exhaust flow should be broken up within the manifold with sharp turns, abrupt connections, dead ends, etc. This "log" design (as it was referred to then) was supposed to benefit the turbo's gas flow to the turbine somehow (something about countering pulses or such). So a straight large tube was run the length of the head with short, smaller diameter tubes at 90* from the ports....kind of like this:
I never pursued that turbo project and haven't kept up with the latest theories. Now I see many of the more recent manifold designs seem to have gone in the opposite direction, trying to maximize gas flow between the ports and the turbo. Some general examples:
These tend to be most popular for the Asian imports, so I'm not sure if this is mostly for 'style' (looks) or if they have a true design benefit with turbo applications. I'm of the understanding they tend to suffer from cracking, leaking, heat management issues, etc. A turbo is heavy and therefore a lot of weight to be hanging off a bunch of twisted long tubes, vibrating constantly while enduring excessive heat cycles.
The more modern version of the "log" design (like "lanciahf" and "stingray250" have shown) appears to be a much better execution of the earlier theory. The shorter runs, heavier materials, smoother shapes, and simple design should be strong and durable, while offering decent flow and good heat management.
Hope others can offer the current theory on turbo manifold designs. Is achieving maximum, balanced flow the bigger goal, or quick, hot gas transfer to the turbo inlet more beneficial?
