Quote:
Originally Posted by pastry_chef
This would be FAR from ideal!
that scenario would have a severe negative impact on what is commonly referred to as the "5th cycle" near TDC to draw intake charge.
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Dont bet on it. 1st off it would not likely be possible to acheive that condition and if you did it would pretty much accomplish the same effect. Study "5th cycle" a bit more closely. It occurs on running engines even granny's car to a small degree. Cylinder fires near tdc, as it approaches bdc the ex valve opens. A large pressure front begins to head out the exhaust. By time piston nears tdc that high pressure front is somewhere down the pipe. Behind that high pressure front is a lower pressure "front". Lows always follow highs. the charge is literally being "pulled" by the high. This is how the intake charge can begin moving into the chamber while the piston is still in TDC dwell.
Yes header tuning/valve timing can enhance the effect. However if you did accomplish no pressure on the upsweep you wouldnt need to enhance the scavenge effect as it would already be accomplished.