Dave Plowman (News) wrote:


But a true one. Exhaust gases are under highish pressure. Inlet merely -
at best - atomospheric. On the cylinder head and inlet manifold attention
to the inlet tract by reducing restrictions etc that shouldn't be there
but are due to the costs of removing them in manufacture, etc will pay far
more dividends than the same work carried out on the exhaust ports. And
most production cars are already fitted with free (enough) flowing
exhausts.


Generally increasing the inlet flow means you get more charge in the
cylinder and more power. Increasing the exhaust flow reduces
backpressure and helps the inlet charge too but to a lesser extent.
Becasue there's less backpressure you get better mpg. Increased inlet
flow increases power. Do both and you're onto a winner.