Manifold Development Process. Manifolds as Individual Components

The essential steps in manifold development are listed below:
- Customer query for a desired manifold concept
- Customer specification of the available installation space (may also include the geometry for the draft concept as well as that for the cylinder head flange, exhaust flange geometry, space available for power driver use, surrounding engine compartment geometries, etc.)

- Specification of loading data (engine type and performance, vibration induction by the engine and/or road, exhaust gas temperature)
- Definition of the emission standard (EURO 3 or EURO 4 or some other norm)

- Development of a detailed concept and the design created using CAE tools including, for example, heat transfer calculations, calculations for flow mechanics, or FEM calculations
- Construction of samples with tooling similar to that to be used in mass production

- Certification testing at either the developer’s or the customer’s site
- Customer’s production approval for the development
- Test with mass-production components to verify the design
- Construction of mass-production tooling
- Production launch

As a rule, the overall period between the inquiry and production launch is about two years. Development work today is carried out in only a 14-month period; eight months are consumed in pure development time, and the remaining six months are required to build mass-production tooling and set up the manufacturing lines.

Manifolds as Individual Components. Cast Manifold (Fig. 7-335). Typical materials:

Nodular gray casting (GGG), SiMo gray casting: Nodular gray casting using silicon-molybdenum (GGG-SiMo), SiMo gray casting with vermicular graphite, austenitic cast iron (GGV-SiMo)

Wall thicknesses:
- 7 to 8 mm for GGG manifolds
- 2.25 to 4 mm for chilled casting

Fig. 7-335. Cast manifold for four-cylinder gasoline engine

Advantages:
- Compact design
- Wide latitude in designing the shapes
- Good acoustical properties with high material damping properties
- Economical ($15 to $18 for SiMo casting).

Disadvantages:
- Great weight.
- The maximum permissible exhaust gas temperatures for cast material are limited.
- If, because of the extreme temperatures, the use of nickel alloys is necessary, then the price will rise to between $35 and $40.

- Cast manifolds operate in a temperature range that can affect service life (bad for endurance, considering the engines’ higher performance densities and resultant higher temperatures).
- High surface temperatures (heat shielding required).

- Critical in emissions following cold start because of the manifold’s high thermal masses.
- Severe postheating properties because of great thermal mass.
- Any desired or optimized runner lengths can be implemented to only a limited extent with cast material (performance optimization is limited).