View Single Post
Old 03-18-2015, 12:40 AM   #268 (permalink)
Master EcoModder
ever_green's Avatar
Join Date: May 2011
Location: Toronto
Posts: 264

gueff - '19 Mercedes Benz A250 4MATIC AMG
90 day: 30.55 mpg (US)
Thanks: 8
Thanked 79 Times in 33 Posts
While tuning my naturally aspirated 2.5L Subaru on the dyno i spent an extra $150 and did some part throttle pulls to find BSFC sweetspot. Since dyno pulls are expensive I only did 4 runs of roughly 15, 20, 25 and 40% throttle. I cannot vouch for the dyno's BSFC estimation accuracy but it used torque at wheels, injector pulse width, rpm, mas air flow and other data. the efficient region seemed to be at a very narrow engine load and speed of 1800rpm @5"Hg vacuum. Any more vacuum (or smaller throttle opening) or engine speed resulted in the BSFC suffering in an exponential manner. even lean burn mixtures and high ignition timing could not make up for pumping losses at high vacuum.
  • 40% TPS run reported ~13.9 AFR w/full manifold pressure (no vaccum)
  • lower throttle positions were in locked Torque Converter mode with ~14.3-14.7 AFR

here it is in a graph form:

  Reply With Quote
The Following 3 Users Say Thank You to ever_green For This Useful Post:
P-hack (03-18-2015), Piwoslaw (03-18-2015), some_other_dave (03-20-2015)