Large diameter pipe step down to smaller pipe

[damunk]

Can I ask why from the test piece you see in most setups a large diameter pipe connected to smaller diameter pipe going to the motor?

Some designs have a same diameter pipe all the way to the motors but I wanted to know why people step down the sizes of pipe

[Tony]

The cylinder head MUST be correctly centred and mounted over a piece of pipe that is exactly the same diameter as the cylinder bore of the engine.
Anything larger or smaller can effect the flow through the valves, so you try to make this pipe as exact as possible.

After a short distance this pipe can feed into either a large settling chamber, or a smaller pipe, or may stay the same diameter, depending on the type of flow bench.

[damunk]

Thanks Tony,

You've probably seen this link. I found this a good read.

http://www.dtec.net.au/Tech%20Articles/ ... Design.pdf