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Tri-Y headers (4 into 2 into 1) seem to be
the latest thing in “Welterweight” racing. In the mid 60’s I was
designing V-8 headers for Jardine Headers, and Tri-Y’s were common
place. The tube arrangement was such that it partially corrected the
misaligned firing order of V-8 engines. In recent years some Tri-Y’s
have been used on four cylinder car and motorcycle applications, but
not much in circle track racing.
To get a grasp of the difference in the power band between a 4 into 1
and a Tri-Y header, you only need to have a look at the dyno curve of
the two headers run on the same engine. The power band on a 4 into 1
is a narrower, more peaky (concentrated in a narrower RPM range),
where as the Tri-Y has a broader, flatter power band.
One advantage the Tri-Y has is the “Steptube” effect. The 4 primary
tubes collect into two secondary tubes that are usually two sizes
bigger in diameter. The two secondary tubes then collect into a single
outlet, which is usually two sizes bigger again. This increase in
volume slows the velocity, increasing the scavenging.
A 4 into 1 header using a “Merge Collector” (having the pyramid in the
center) and rotational firing order can generate as much as 12 lb of
vacuum inside. Using the same two sizes bigger formula, the collector
outlet is two sizes smaller than the Tri-Y outlet. This generates a
great deal of power in a narrow RPM range.
At this point you have to rely on the track condition to help you
determine which header is best for you Are you running a big track
where you never have to lift and you are always near Redline, or a
tight track where your RPM falls way off?
If you know your engine’s operating RPM and you put it on the dyno,
you can learn a lot.
I’m shutting her down till next time. “Keep it Right Side Up”
Loren Barnes
President S&S Headers Inc. |
