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As
you can see in the photos of my new Prototype Racing stainless steel
equal length 4-2-1 exhaust header for the Honda K20A in the Elise, it
certainly isn't easy to build. An easier route would've been to design
a shorter header that would make more top-end power, but a nice broad
torque curve is more important, and that's what I designed this one
to produce. I had to wait many months to finally get the proper radius
bends with which to bring the image in my mind into reality. Previously
I used the first section of the Japanese Type R exhaust header, and
built onto it to get the proper overall length, but the tube size and
rather short primaries were hurting torque production. Look at the new
Dyno curves, and you'll see what I mean. I'm quite pleased with the
way this "hot snake orgy" works, and even though it's extremely expensive
to produce, it will be the standard exhaust header included in the K20A
kit, and will bolt right up to your existing CAT or replacement pipe.
We made substantial changes in ECU mapping for fuel and cam angle phasing
to compliment the header design, and that mapping is available as part
of the Hondata ECU upgrade, and immobiliser deletion.
Considering that we started with an engine rated by Honda at 220 HP
@ 8,000 RPM (measured at the crankshaft), I think we've done quite well
in broadening the torque curve substantially, and producing approximately
55 more HP at a lower RPM with no internal modification to the engine.
This was accomplished using the standard Exige silencer, and running
the engine on 91 Octane fuel. At this point I think we've come to the
end of the first phase in the tuning of the K20A. The next phase will
include new cams and reshaping the intake and exhaust ports to provide
us with superior airflow. I'll concentrate my efforts on letting the
engine breathe better before I start changing pistons, etc.
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