I was reading that an engine is more efficient when the intake and exhaust temperatures are close together, ideally being the same. Why then do we have the cold air intake? or am I misunderstanding things? Anyone have any thoughts? Cold air intake, colder air or better flow, as to why it works better than the OEM intake.

Boyles Law my friend. . .

The lower the temperature of a gas the less space it takes up. So to fit more gas in the same space, cool it.

Or, and you'll like this: Pressurise it!

And then add fuel to suit.

Cold air is denser there for more oxygen per each part of air which equals a better burn. Plus keeping temperatures low reduces the chances pinking as temps are low stopping it firing before the spark has even gone off or the pitson is a top dead centre.

I think the only advantage of hot intake temps is low speed running. The fuel atomises with the air better. That why it keeps emmisions lower.

Quote:Perhaps "most efficient" is not the same as "most horsepower" ...

Best site I have found about engine theory that gives it to you straight is good old Puma Racing (an engine builder in England)

http://www.pumaracing.co.uk/mainmenu.htm

That should get you sorted

You read right.(as far as thermal efficiency is concerned) thermal efficiency = work output/heat in.
work output = heat in - heat out.

therefore, efficiency = (heat in - heat out)/heat in.

so if you reduced the heat out to 0. you would have 100% thermal effiency.

so if the exhaust was the same temp as the intake...you have zero heat leaving..

Note heat in is the heat created from burning fuel.

For a fuel to burn it needs oxygen. You have cold intakes to increase the density of air, and in efi, to allow more fuel to be injected. Note if you get more power from your engine, does not mean it is more efficient...not if efficiency is measured as thermal efficiency.

Quote:

And quite often it means that you can wind a little more advance on for further tuning gains.

Just checked the link and it didn't work, try this one for Puma Racing

http://www.pumaracing.co.uk/

i guess the exhaust as will be cooler in part because they expect you you to use something regenerative like a turbo to extract more thermal efficiency.

" guess the exhaust as will be cooler in part because they expect you you to use something regenerative like a turbo to extract more thermal efficiency."

What???????????????????????????????????????????????

A turbo does take "wasted" heat from the exhaust to create power...however the extra power creates extra heat plus it requires more fuel. If you are suggesting (I really don't understand what your trying to say) that a turbo makes an engine more thermally efficient...well I don't know..

I spose a fuel efficient engine may have a high thermal efficiency value..a high horsepower engine however...may not necessarily? be highly thermally efficient????

I know my first statement is pretty much on the money, the rest...well car engines are quite complex.