I'm a bit late to the show on this one, but the prospect of a flat-plane Mustang intrigued me somewhat with the revealing of the GT350R. Then I hear the engine itself sounds somewhat un-flat-planey: doubly intrigued.
Now, this is not really new:
These are both flat-plane V8s with the "classic" log manifolds, feeding equal secondaries and X-pipes. The resulting sound is effectively a combination of four 90 degree V-twins that remain distinct due to the specific combination of equal and unequal lengths in the exhaust. Lose the equal secondaries or the X-pipe, and you get
this.
But the 'Stang doesn't quite sound like that "classic" approach. For me, it's sort of a mix between the modern Corvette sound and the "hot-vee" twin turbo V8 M5 / M6 (which in turn sound like a duplexed boxer 4, to me).
Based on that, we can almost directly infer the manifold configuration. We know it's using "long" (for production standards) tubular manifolds, so it should be easy to get the differences required in the individual runner lengths.
Log manifolds aren't really conducive to high ouput in NA guise, but their acoustic effect can still be approximated with e.g. a "swept back", aftermarket-style tubular manifold with 4 separate runner lengths.
Alternatively, it should be eminently possible to isolate the front cylinders from the rear with only 2 slightly different runner lengths. That latter approach, in conjunction with equal secondaries and a "perfect" X-pipe, effectively gives the sound of a cross-plane V8 with perfectly equal length primaries and secondaries coupled with an H-pipe (or unequal secondaries and Y- / X-pipe). This would sound something like an R8 V8, on the exhaust side only.
Those Mustang GT350s still sound like the configuration is something more complicated / muddled, however, possibly like the old Cobra Daytona (i.e.
this and
this), re-factored as a 4-into-1 and the pairings preserved instead via runner length. It might, then, (although it's unlikely) be the result of trial and error...
Alternatively, any subtle separation of the banks (i.e. non-equal secondaries and / or non perfect X-pipe, or H-pipe instead) would quickly destroy the effect, and unearth the "flat-plane-ness", as with the Esprit above. The same would be true with primary runners that were too equal in length, regardless of everything else.
As a final possibility, and thinking again about "trial and error", they've maybe paired the "wrong" cylinders in the Daytona Coupe style separation of runner lengths. It's quite easy to get some lumpy but not quite V8-y sounds that way.
A combination of "wrong pairings" and the bank separation would probably best explain the sound I hear.
Maybe they can fettle it before release, but changing the manifolds affects engine performance and NVH, so...
Perhaps this was deliberate, in that it is the quietest combination, requiring less silencing volume (and hence mass).
Now, back to that age-old alchemist's question: how to get a V6 (new GT...) to sound like a V8?
" if you understand my point of view...
