Quote:
Originally Posted by Td-d
What?
|
Knock sensor equipped engines develop peak bmep until they knock. Cold weather doesn't reduce the detonation point.
Intercooler equipped turbo engines can develop higher torque because the compressed intake charge is cooled effectively by very cold weather, but in the intercooler.
Cold ambient air doesn't affect combustion chamber temperatures by any significant amount. The higher the compression ratio the less the starting air temperature affects pre-ignition charge temperature. Detonation results from end gas spontaneous ignition prematurely caused by the compression wave resulting from the flame front. That in turn limits bmep which limits peak torque. Knock sensors permit combustion pressures to rise up to that point and not beyond.
Therefore, if this engine is controlled by knock sensors then it produces its highest bmep at the point the knock sensor operates.
It is true that colder intake air is denser and therefore an engine not already optimized will run better in cold temperatures than in warm temperatures. This is not the case off engines controlled by knock sensors unless turbo intercooled.
Remember that the key advantage of direction injection is charge cooling resulting from cool fuel sprayed directly into the hot compressed air in the combustion chamber. The starting temperature of that air is pretty much irrelevant now.
This is one reason "cold" air intake modifications won't produce any meaningful extra power out if these engines and because the stock air box is pretty efficient already there are no real flow advantages available either.
While an engine develops higher torque as it ingests more air mass it cannot exceed its designed detonation limit.
If you drove in the 70's and then when the first knock sensor equipped engines came out in the 80's you would realize this.