http://www.mazda.com/en/innovation/technology/skyactiv/skyactiv-g/Mazda says a Tr-Y header
with the tube length down to the 2nd Y join
of 600 mm (23.6 inches)
has several benefits
Back in 1994 Mike Leach made for Magnum 5.2/5.9 V8s TriY headers that Mopar Performance put their name on that had a combined tube length to the second Y close to this.
How much does this help?
In 2012 when Mazda could NOT fit this 4-2-1 header into the Mazda3 engine compartment space then available, but had the other SkyActiv changes on the engine,
static compression ratio in the USA sold model was 12 to 1.
In 2013 when they could fit the 4-2-1 header in,
static compression ratio was raised to 13 to 1.
Overseas where gasoline Octane rating of regular grade is higher than the USA AKI of 87, Mazda raises the static compression to 14 to 1
