trinidefender wrote: ↑
Fri Mar 27, 2020 3:27 am
Why would pulse tuning not be a factor. It will still provide "free" turbocharging at the correct rpm regardless of if there is a turbocharger there or not.
Usually what I see is that in the aftermarket road car tuning world, pulse tuning with turbochargers generally is far lower on the priority list. The aftermarket guys tend to run large (and often mismatched) turbochargers chasing big power numbers and then have to compensate with short compact runners to minimise lag (spool time). After that extra boost and dumping fuel at a rich mixture to stop detonation is done. Long story short, in that world, chasing power is generally done the sledge hammer way (stronger block, bigger turbo, more fuel), they aren't so concerned with chasing the few extra hp with high expense that pulse tuning might bring.
F1 is a completely different game with lag being almost non-existent due to the MGU-H. In F1, fuel flow is an issue where the engineers are trying to pull every little bit of power out the fuel as possible. Hence why every PU manufacturer went with variable length trumpets as soon as they became legal. They also have the budgets and facilities to chase these slim margins.
My understanding of tuning of header length is based on two principals;
1. Helmholtz- the energy imparted on the column of gas be the exhaust valve closing reflects of the open* pipe end back off the closed valve prior toit's next opening event. *open also being a change in volume.
2. Scavenging- the exhaust pulse from one cylinder creates a depression at the merge collector creating a depression in the adjacent cylinder header pipe.
With a turbo application, there is no open end therefore the reflection is limited if not non existent.
Scavening may also be limited as the pressure in the header is always positive (unlike an NA engine) so that depression of say 10KPa is less significant when looked at against exhaust pressures of 300KPa.
This is all based around a fixed length is optimised for a fixed rpm. The desired rpm will dictate the length. If the operating rpm is 9-12krpm then the length is fixed. If that length cannot be package in Hot Vee without impacting packaging then it can't be implemented.
Additionally, blowdown effect of the positive pressure of the exhaust leaving the valve is reduced over length as the gas cools and is not specific to a particular rpm. This loss may be bigger that the gains from a length of exhaust header which works only at one rpm.
Another point is that these engines are not air limited. They run with excess air. More air may not equal more power.
The more I think about it the more I feel that Hot Vee may be most beneficial from a blowdown point of view that a tuned length.