Duder
Watch it man, there's a beverage here!
- Joined
- Dec 9, 2009
- Location
- Torrance, CA USA
Duder- that was why I decided on my design (it’s in the recent page of the build thread) mid length 4-2 twin scroll header, 14.75” near equal length +/- .25” to merge, then the intake is right around 11.75 total length with enough room to decrease to 10” or increase to 13”. Looking at Indy car stuff and seeing how most designers have come pretty close to equal volume on either side of the turbo system, and some of the things gathered from people I’ve met through work as well as picking your brain some, I feel like I should see benefits in low-mid-high rpm as well as significant gains in transient response. Basically I’m shooting to get net volume from valve to wheel as close to equal as possible in order to maintain high efficiency of transient response, if that makes any sense.
It does make sense! Good deal man. Having equal pulse timing is key for transient response; as the pulses impinge on the wheel you get a much higher apparent turbine efficiency with those "staccato" hits of energy and momentum transfer. It's not a steady-state phenomenon, in other words. If the flow paths are unequal in length or volume then the exhaust pulses themselves can interfere, lose energy, and diminish the gains. The whole twin-scroll housing concept is based on this but it applies for any radial turbine really. A 3-cylinder engine is perfect for transient pulse tuning without the need for twin-scroll; same exact benefit is seen with twin mono-scroll turbos on an inline six.
The wave reflection stuff is of course key for engine breathing and VE across the entire rev range, cylinder filling, and so on. As far as the turbine is concerned though the pulse effect becomes severely diminished as engine speed increases. So you can optimize your turbine match for good steady state / high flow / high engine speed efficiency but then tune the pre-turbine exhaust system to give good pulse effect at low speeds but also better engine breathing at high speeds. It's fascinating stuff really!