Or possibly going to 71mm compressors and keeping the 73/80 turbines?
how much effiency and performance change is lost or gained using the same compressor/turbine size and running it as a high pressure stage or even a single?
For example if with a given turbo the compressor has enough wheel for the requirements but it is choked on the exhaust size would the option to go up a wheel size on the turbine and keep a tighter a/r be better than just going up in an a/r size on the original turbo?
I should clarify, either the low pressure or high pressure turbo in a two stage setup can benefit from maximizing the compressor size for the given turbine size. The issue with this practice in a single stage setup is surge, in a high pressure situation such as diesel engines commonly see it is exaggerated.
With that being said, how much does opening up the MWE groove actually affect the surge line itself, versus the actual MAP overall.
That would most likely depend on the groove's location and size, but I wouldn't expect miracles.
Like for a fuel only Cummins, 500-600hp. Would it be better to use a 63/99 or a 63/84? Since the Cummins are more restricted in the head, would a higher PR help? Making the 63/99 more desirable?
Now why would a 71mm drive a turbo harder than a 68? I am guessing it captures more exhaust but would it improve response?
Like taking a HT4B and using it as a primaryin compounds, Weston?
What about turbine trim? How does it relate to spool up and what factor does the speed of the exhaust pulse play into turbine selection.
In my opinion no. Since surge is not an issue in a compound arrangement, I see it wise to maximize the potential of the compressor given the adjacent turbine size.
The exhaust gas entering the low pressure turbine will not be steady state, but if you are referring to it being more linear as in not seeing the engine pulses directly, then yes the high pressure turbine should subsequently dampen this.
I would also make this assumption, increasing the turbine AR is somewhat of a crutch to avoid choke flow, the only two real solutions are a wastegate bypassing the turbine or a larger turbine wheel itself, both of which are incorporated in most factory equipped compound setups.
A very common twin setup is the 66/73/.91 or 14cm paired with an s480 using a 96/88 Exhaust wheel and 1.32 housing. Most can break 950hp with this setup and some have made 1100+ on a commonrail with fuel only. My question is, do you think running the same 66 with an s480 with an 87/80 turbine and 1.10&t6? Would make more power? Or even 66/68/.91 with an s480/87/1.10t6?
It's opposite to compressor so lower trim, like HT4 or S4, works with old large manifolds that make more backpressure and lower exhaust velocity. High trim turbines like HX60 97/92 need modern tight manifolds with high exhaust velocity and low backpressure.