The Importance of Cold air for Engine performance

The importance of cold air for engine power cannot be overstated. The colder the air being drawn into the air, the denser it is. The denser the air, the more oxygen it cantains to help burn the fuel = more power. This was graphically illustrated when we ran one power run with the engine comparment enclosed. The intake temperatures soared and the expected power gain from fitting a cone filter was completely lost. From Paul Sharpe's engine bay temperature studies, the area occupied by the cone filter is probably one of the hottest areas in the engine bay! Interestingly, the standard system's air intake draws air from the coolest region of the engine bay- this is sure to be  no co-incidence.

Two of the performance cone filters tested during this investigation were equipped with ram-cooling ducts, that duct ambient temperature air and direct it towards the filter itself. The other two filters, from Pipercross, do not offer this refinement.

Do these cooling ducts work? From data collected by Graeme Bishko, the engine bay ducts do indeed work well. At motorway speeds, Graeme found that temperatures at the filter were reduced by up to 30 degrees celcius. There is a problem with the cooling duct arrangement however. At standstill the temperature at the filter quickly rose to ambient engine bay temps- not ideal for those standing starts from the lights!

Positioning of the cooling ducts and the filter is important to obtain the most advantage from the cold air. Indeed, the fabrication of an airbox to separate the hot engine bay from the cool intake air would be the best solution of all- and this is exactly what Carl in Sweden has striven to achieve. No rolling road results are available unfortunately, but the result is likely to be effective assuming that radiant heat is well controlled.

An alternative to the under car ducting is to draw air from the left hand engine air intake, an approach championed by Roger Parker. From moving car observations with tickertape over the grille and surrounding body work, the air intake has very little air either into or out of the engine compartment. In fact, from these observations, the air flow is practically stagnant- which means that the engine has to actively suck air into the intake system. Whilst initially this could be viewed as a disadvantage, it does mean that this source of air is at higher pressure than the surrounding fast moving air moving around the side of the body work. Bruno in Portugal undertook some rolling road tests with his VVC so equipped, and these are posted here. Those in the MGF racing community who have converted from cones to filters with cold air intakes of this pattern report palpable improvement in the engine's responsiveness. I hope to modify the filter system in my own car to verify whether this system offers any advantage over the more 'conventional' K&N 57i set up.

This page is under continuing development- please revist here soon.