[nmhancoc]

Not the one you were responding to, just a car nerd.

> You say that flat-plane engines do not require the complex header primaries that have to cross over from one bank to the other, but AFAIK typical road car and truck V8s do not have such headers[1]. Would the purpose of such headers be to give a cross-plane V8 scavenging about as good as a flat-plane one, all else being equal?

Yes, but as you point out deployments of this technique are limited due to packaging, cost, and even other performance parameters. See the GT40 “bundle of snake” headers for an example.

For a notable example of the other performance parameters, exhaust header lengths are tuned to the powerband of the engine such that shorter headers are more efficient at higher RPMs and longer headers at higher RPMs. This can even get into resonant effects as with intake runners. It’s difficult to design cross bank headers short enough to suit modern high-rpm engines, with the exception of the “hot-V”, exhaust inside intake outside, concept deployed on German V8s from BMW, Mercedes, and Porsche on the 918 (though the latter is a flatplane crank).

> In that case, would the cross-plane engine lose most of its distinctive sound?

Yes