This is the type of engine these headers are designed for.
The Chevy Indy V-8’s even-firing 180-degree crankshaft produces an exhaust note with a high pitch and an exotic sound.
One of the key components in the Chevy Indy V-8 is its 180-degree crankshaft. A conventional V-8 crankshaft has its four connecting rod pins at 90-degree intervals; the Chevy Indy V-8’s crankshaft has its rod pins at 180-degree intervals. This design is often called a flat crankshaft because the pins are in a single plane.
With a 180-degree crankshaft, the cylinders fire evenly from bank to bank; this produces an exhaust note with a high pitch and an exotic sound. The 180-degree crankshaft can be lighter and stiffer than a comparable 90-degree crankshaft, and offers the potential to improve engine performance by optimizing the exhaust tuning.
The distinctive sound produced by a 180-degree crankshaft is due to the timing of the exhaust pulses. With a conventional 90-degree crankshaft, two of the cylinders on each bank fire in succession, and two cylinders have longer intervals between firings. These irregular intervals between exhaust pulses produce the low rumble that’s typical of the racing V-8 engines used in NASCAR.
With the 180-degree crankshafts that are used in the IRL, the cylinders fire alternately from bank to bank in even intervals. This regular exhaust note is like a musician beating rapidly on a drum — the note almost becomes a continuous tone. These even bank-to-bank exhaust pulses, in conjunction with higher engine rpm, produce an exhaust note with a higher, more ‘exotic’ pitch.
The 180-degree crankshaft design offers several advantages for a high-speed racing engine. It can be lighter and stiffer than a comparable 90-degree crankshaft. The lighter weight reduces the crankshaft’s inertia, so there is a potential for quicker acceleration on a short-track. The 180-degree design also has the potential to improve engine output by optimizing the exhaust tuning.
The chief disadvantage of a 180-degree crankshaft is that it is inherently unbalanced. A V-8 engine equipped with a 180-degree crankshaft is essentially two four-cylinder motors joined by a common crankcase. And like other inline four-cylinder engines, the movement of the pistons up and down in their cylinders causes a perceptible vibration. In contrast, virtually all production V-8 engines use a 90-degree crankshaft, a design that is inherently balanced and produces the smoothness that is characteristic of a V-8 engine.
“Inline four-cylinder engines have a vertical shaking force,” explained GM Racing engineer Ed Keating. “Many production four-cylinder engines use dual balance shafts that run at twice engine speed to counteract this vibration. In a racing environment, the additional weight and packaging requirements of these systems make balance shafts impractical.”
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