bsfc efficiency with a manual trans

[dcb]

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.

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.

[busypaws]

We've done A/C deletes, Power Steering Deletes, Alternator deletes.
How about Clutch delete?

[bgd73]

I wonder what vw did with the oil pump for operating ranges..

lo and behold a flashback to an old rabbit I drove, it was one of the reasons for adjusting valvetrain more often than casual.. never needed rpms. the oil pump did however.

they must be smarter than that today.

[PaleMelanesian]

I like to look at shifts in terms of where the rpm will land after the shift. There's a minimum usable rpm, and I aim for that. For example, if my minimum is 1200 rpm:

Shift, speed, rpm before / after
1-2, 12 mph, 2480 / 1240
2-3, 17 mph, 1760 / 1175
3-4, 23 mph, 1580 / 1188
4-5, 29 mph, 1498 / 1199

So I'm shifting at 2480 rpm, then 1760, then 1580, then 1498.

[dcb]

do you have a bsfc map link somewhere for your car? I'd be curious to see how those shift points correspond to bsfc peak.

[PaleMelanesian]

I'm just going by the general ones available. I've found that the BSFC maps are a good start, but keeping the rpm to the lower side is better than the higher side. With your map above, that means more 1500 and less 2000. But that's just what I've found with my car over 3+ years of fine-tuning. If I had to guess, a TDI would do similarly well, or even better, at low rpm.

[dcb]

ah, well I ran out to get the numbers from the saturn, really just getting a handle on the ratios. I think it will take a program or fancy algorithm to minimize the distance from bsfc peak. At thats at least where I think this is headed, i.e. put in the mph/rpm for each gear and a target bsfc rpm and get the "optimal" shift points.

shift @2000 rpm
gear     1    2    3    4    5
mph     12   20   29   39   55
rpm1   800 1200 1379 1487 1418

Here is the BSFC for a saturn, so shifting @2000 rpm would never approach bsfc peak. Shifting @ 2800 would be pretty well centered and keep within %95 of peak bsfc, assuming you have a well tuned foot and buttmeter and can keep it at 125nm.