Quote:
Originally Posted by Td-d
I'm well acquainted with the reasons why cold air allows for greater air-mass, and the functioning of intercoolers - I just really struggled to follow your logic.
The problem with this theory lies in that first sentence - this is not how the Subaru knock strategy works. It's a more reactive process - see here. It's also a curious question as to whether the BRZ is knock sensor controlled, since I suspect every ODB2 compliant vehicle since 1996 is likely to have knock sensors (I stand to be corrected).
I agree that direct injection reduces in chamber temperatures, that's the whole advantage, but DI is not used at all load ranges. |
I read the link. Not sure what you mean. Knock corrected engines run maximum ignition advance possible (I'm generalizing a bit) and then retard ignition as needed when knock is detected. Pre knock sensor engines couldn't do this so maximum ignition advance was always set at less than the maximum possible. The other link in that tuner thread expands a little:
http://www.romraider.com/RomRaider/H...ndKnockControl
Just because the software only corrects by retarding the ignition doesn't make it "one way" which is what I think you think. If you start from maximum possible advance under ideal conditions then of course the correction will be one way. But that is an illusion since the system could as easily work in "both" directions. Ignition timing is no longer linear but 3D mapped. So it is an oversimplification to say the ignition is always retarded by the knock sensor. Really the knock sensor just modifies the ignition timing map in a designated way. It will always retard the ignition when knock is detected and advance it when knocking ceases, in a continuous feedback loop. There is no room for cold intake air to affect bmep in this system.
Similar systems controlling turbo boost can appear to be two way but isn't really, it's one way in the other direction. Base boost is fixed at a safe level and then the wastegate controller is "tricked" into "seeing" less boost pressure than is actually present in the intake. The boost pressure is permitted to rise until either the engine detonates or a pre-set maximum boost pressure is reached. Then boost is reduced progressively until detonation ceases and is permitted to build up again. This is a feedback loop.
Both systems operate on the same principle: feedback loop.
Cold air cools an intercooler very effectively permitting additional boost observable even on a non calibrated boost gauge. Also, in very cold conditions the over boost cut out is more readily reached.
For our highly tuned engines cold intake air can make no discernible difference in power output. I am happy for anyone to show this to be wrong by dyno or other means: increase in too speed observed or quicker acceleration times.