Exhaust Exhaust Manifolds & Headers 2 — Questions and Answers
Question 1: What is 'exhaust scavenging'?
- Filtering pollutants from exhaust gases
- Using exhaust pulse energy to help draw fresh gases into the cylinder (Correct answer)
- Removing carbon deposits from the manifold
- Testing exhaust flow with a vacuum gauge
Correct answer: Using exhaust pulse energy to help draw fresh gases into the cylinder
Exhaust scavenging uses the negative pressure wave created by an exhaust pulse to help pull fresh intake charge into the cylinder, improving volumetric efficiency.
Question 2: Which type of header is best suited for maximizing low-end torque in street performance applications?
- Shorty headers (Correct answer)
- Long-tube headers
- Equal-length tri-y headers
- Lakepipe headers
Correct answer: Shorty headers
Shorty headers are less disruptive to low-RPM exhaust scavenging characteristics, making them better suited for street driving where low-end torque is prioritized.
Question 3: What sealing component is placed between the exhaust manifold and the cylinder head?
- Valve stem seal
- Head gasket
- Exhaust manifold gasket (Correct answer)
- Throttle body gasket
Correct answer: Exhaust manifold gasket
An exhaust manifold gasket seals the joint between the manifold and cylinder head, preventing exhaust gases from leaking and causing noise or damage.
Question 4: What symptom commonly indicates an exhaust manifold leak?
- Rough idle only when warm
- Ticking or popping sound from the engine bay that diminishes as the engine warms up (Correct answer)
- Black smoke from the tailpipe
- Loss of power steering assist
Correct answer: Ticking or popping sound from the engine bay that diminishes as the engine warms up
A cracked or leaking exhaust manifold often produces a metallic ticking sound when cold that may reduce as the metal expands and partially seals the crack once warmed up.
Question 5: What is the purpose of ceramic or thermal coating applied to exhaust manifolds?
- To prevent corrosion only
- To retain exhaust heat inside the pipes, improving flow velocity and reducing under-hood temperatures (Correct answer)
- To dampen exhaust noise
- To meet emissions requirements
Correct answer: To retain exhaust heat inside the pipes, improving flow velocity and reducing under-hood temperatures
Thermal coating keeps exhaust gases hotter inside the manifold, maintaining gas velocity for better scavenging, while also reducing underhood radiant heat.
Question 6: What is a 'collector' in the context of performance exhaust headers?
- The gasket that seals the header to the head
- The section where individual primary tubes merge into a single outlet (Correct answer)
- The clamp joining the header to the downpipe
- The oxygen sensor bung
Correct answer: The section where individual primary tubes merge into a single outlet
The collector is the funnel-shaped section at the end of an exhaust header where all individual cylinder tubes merge into one pipe, which then connects to the rest of the exhaust.
Exhaust Exhaust Manifolds & Headers 2
What is 'exhaust scavenging'?