hoffman900 wrote: ↑Mon Jan 06, 2020 6:33 pm
digger wrote: ↑Mon Jan 06, 2020 6:30 pm
OEM considerations (emissions, economy etc) for their camshaft choice is probably not the purpose of this thread where the stated method is for WOT performance
It isn't, but check out to the two Honda figures showing overlap changing as a function of engine speed and load (which I assume would be torque production by the engine).
Yes if you have variable cam phasing then the ECL or ICL (i.e. LSA) or are not going to be fixed vs rpm at WOT for optimization of VE at each rpm.
This does not mean that in the case of fixed timing engine that there isn't a cam phasing that’s optimum for a specific (consistent) set goal.
I ran a bunch of cam options in ENGMOD4T single pattern cam straight up various ICL/ECL (i.e. LSA) on same engine with no other changes.
It showed that with various durations (5 of them and each on 5 centrelines) there was an LSA that made best average power in the rpm band that would match something like the EMC 3000-7000rpm band irrespective of whether it was a 270 cam or 310 cam (seat to seat durations) which happened to be very tight like 102 IIRC
this seems to agree with David’s work about the LSA being “fixed” (not that I agree with the methodology put forward as i would have separated out ICL and ECl and looked for trends in those separately rather than LSA with more time)
There are a number of flaws with my test, as I did NOT:
- optimize exhaust and inlet configurations (lengths, pipe sizes, configuration) to suit the different cams that would tend to want to operate at different rpms.
- raise the CR with increasing duration
- advance or retard the cam. I just ran straight up single pattern where ICL = say 102, ECL =102 and therefore LSA also 102
- I was calculating best average power over a very wide rpm which is not always the goal for every application e.g. a high rpm narrower rpm band would be able to use a wider LSA but only slighty.
from some of the test ive done I don’t think this invalidates the sims e.g. a change in runner length hasn’t seem to warrant a change in centerlines but thought id put it out there that this isnt a conclusive set of answer merely a trend.