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dcb · 05-27-2010, 10:20 AM

with my clutch acting up I've had to rpm match shift everywhere, which of course got me thinking about rpms a little more in general

I made some casual speed observations @2000 RPM in different gears, and computed the next rpm after the shift (rpm1) assuming the car is going basically the same speed immediately before and after the shift.

Code:

shift @2000 rpm
gear     1    2    3    4    5
mph     12   21   32   45   58
rpm1   800 1143 1313 1422 1552

I've included the bsfc chart below so I can see how far from peak bsfc I get with a manual trans. The nice thing about the VW diesels is that peak efficiency is found very near the torque curve, so for most power per fuel pedal position you just wang it open, and watch your rpm.

So with a very simple shift at 2000 rpm strategy, in this car, once you get moving you stay within ~%93 of peak bsfc while accelerating, and have an average efficiency much higher than that. The shift from 1-2 drops you to 1143, close to the 210 line. but also notice that 5th gear starts within the 200 "island" and stays there past 2000 rpm (75mph). So your trip from 58mph to 75 mph is all within %98.5 of BSFC PEAK!

obviously shifting at 2k rpm isnt the most optimal for all gears in this car, the lower gears should probably shift higher, but still the average in terms of bsfc peak from 0 to 75mph is going to be on the high side of %95 with a reasonably educated driver.

05-27-2010, 10:20 AM	#1 (permalink)
dcb needs more cowbell Join Date: Feb 2008 Location: ÿ Posts: 5,038 pimp mobile - '81 suzuki gs 250 t 90 day: 96.29 mpg (US) schnitzel - '01 Volkswagen Golf TDI 90 day: 53.56 mpg (US) Thanks: 158 Thanked 269 Times in 212 Posts	bsfc efficiency with a manual trans with my clutch acting up I've had to rpm match shift everywhere, which of course got me thinking about rpms a little more in general I made some casual speed observations @2000 RPM in different gears, and computed the next rpm after the shift (rpm1) assuming the car is going basically the same speed immediately before and after the shift. Code: shift @2000 rpm gear 1 2 3 4 5 mph 12 21 32 45 58 rpm1 800 1143 1313 1422 1552 I've included the bsfc chart below so I can see how far from peak bsfc I get with a manual trans. The nice thing about the VW diesels is that peak efficiency is found very near the torque curve, so for most power per fuel pedal position you just wang it open, and watch your rpm. So with a very simple shift at 2000 rpm strategy, in this car, once you get moving you stay within ~%93 of peak bsfc while accelerating, and have an average efficiency much higher than that. The shift from 1-2 drops you to 1143, close to the 210 line. but also notice that 5th gear starts within the 200 "island" and stays there past 2000 rpm (75mph). So your trip from 58mph to 75 mph is all within %98.5 of BSFC PEAK! obviously shifting at 2k rpm isnt the most optimal for all gears in this car, the lower gears should probably shift higher, but still the average in terms of bsfc peak from 0 to 75mph is going to be on the high side of %95 with a reasonably educated driver. __________________ WINDMILLS DO NOT WORK THAT WAY!!!