Quote:
Originally Posted by RalliartRsX
You are only partially correct in your statement. The reason the VE head can extend the operating rage is because the head is capable of supporting it. In addition, the head simply outflows the a DE at every single point in the RPM range.
I am not convinced you are aware of just how much more the VE flows over even a heavily massaged DE head with huge cams, which kills power below 6K.
Power is heavily dependent on head flow, not just displacement as you continue to harp on about. That's why it takes the 1stGen 4G63s 20-30 psi of boost to make what a K20 will make at (literally) half that boost with everything else being equal. The 1st Gen 4G63 had some horribly flowing heads.
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An engine can only fill its cylinder to the max. A 2.0L has the same cylinder volume no matter what head is on it. That means peak pressure maximum is always the same, which means peak possible torque is always the same.
And you can't make more power without more torque at the same rpm.
Furthermore, the better the flow at high flow rates, typically the lower the flow at low flow rates due to poor port velocity. So having heads and intakes and cams that flow a lot at high rpm will usually hurt torque at low flow rates, hurt cylinder fill.
Basically to re-state, the cylinder can only fill 100%, it doesn't matter how much the head can flow. Torque is the relationship to cylinder fill, NOT power. Power is determined by overall flow per time, or mass/time flow rate. torque can only go as high as 100% cylinder fill.
Example
sr20det engine at 4000rpm making 300ft*lbs of torque with the stock head (max flow of X), has 99% cylinder fill
Now lets put on the VE head
SR20VET engine at 4000rpm making 300ft*lbs of torque with the VE head(max flow of 2X), has 99% cylinder fill (same)
The engines both make the same torque at the same RPM when cylinder fill is maximum for both, even though one head flows double.
Now, some torque can be gained or lost any number of small ways. Compression ratio. Head design/port shapes/swirl character. Injector timing. Exhaust gas velocity/pressure. Ignition timing, fuel quality, &c So I do believe there is some room to 'gain torque' given the identical displacement; however it is difficult for me to say how much 'different' the VE engine somebody random assembles is to the next thing. Which is why I give general maths and ideas.