[Vwdiesel] Searching the archives (& hill climbing)

[Val Christian]

First, you don't need a tachometer.  Just measure your gear ratios by 
pushing the car (by hand) for one crankshaft rotation (use the flywheel 
mark).  Don't rock things back and forth, because you'll undo the takeup 
of play in the system.  Measure the distance travelled per revolution.
With two people, a cold engine (easier to work by) and a flat paved area,
you can work pretty fast.

Ever accelerate with you vwdiesel, get pushed back in your seat, just
like a shuttle launch, and then all of the sudden, when you hit a 
certain RPM, you seem to go weightless, as the car stops accelerating?
You hit that 4000 to 4500 RPM area.  That's how it works.

With a perfect, continuously adjustable transmission (like rubber wheels 
on cones, not like hydrostatic), you can match your torque need with
the transmission, so that you are operating the engine in the max power
area.  The transmission can be adjusted to give you more torque, if needed.
But you can always operate in the max power region.

With a manual, discrete gear transmission, like you have, there is not
the same ability to ride the max power capability of the engine.  You end 
up having to watch torque, and it is that ability to have the engine 
supply varying torque that makes it feel responsive at less than full 
power. (Because at full power, nothing feels responsive, as you can't 
go any faster.)  So you can ride the torque part of the curve, which will
help you if you have to maneuver or adjust your speed.  If it's a straight
interstate style hill climb, then you hope that you can get the engine
into the max power area.  That will have you climbing faster than if 
you run in max torque.

In general, you get more power as the RPMs increase, because you can 
ultimately burn more fuel.  So running "faster" is going to work better.
There are, however, downsides of high RPM operation, so I wouldn't go 
"screaming" up the hill.   Also, the IP is effectively governed, and 
should not overspeed.   That's good, but it does limit your max speed in
any gear.

Val






> 
> The figure showing the RPM/torque curves is here:
> 
> http://www.4crawler.com/Diesel/SAE/figure_5.jpg
> 
> I think the curve on top is torque.
> 
> I am not sure I understand what you mean by "optimize power". Do you 
> mean to climb at 4500 rpm (appears to be peak power but nearly the 
> lowest torque on the curve). Backing off to 4000 rpm would seem to 
> provide quite a bit more torque but only a bit less power. I don't have 
> a tachometer, but I will try to find out the transmission ratios and 
> calculate the speed for each gear.
> 
> Mark
> 
> 
> 
> Val Christian wrote:
> 
> >Intuitively you're close.  You want to look at the RPM/torque curves 
> >for the engine.  They will be in the SAE paper.  Then look at the 
> >ratios for your transmission.  If in doubt, measure them statically.
> >Then for best rate of climb, optimize power (use the transmission to 
> >get the torque).  50 mph for a downshift may be low.  
> >
> >The temp may climb because the total HP is ideally at max.  Good thing
> >you're at low altitude.  Beat the heat by putting a radiator fan override
> >to force the radiator fan on, like is done for AC.
> >
> >If you can calculate nominal HP at cruise (70 mph?) then you can calculate
> >the power needed to climb the hill. Measure your performance against that
> >theorical need.  You'll take more time, but that's because your transmission 
> >is not ideally matched to the torque needs of the car, and the optimal power
> >RPMs/torque of the engine.
> >
> >
> >Hope this helps a little.
> >
> >Val
> >
> >ps: Without any data in front of me, I'd figure 25hp for 70 mph cruise, 
> >5 hp for engine accessories, and about 20 hp excess.  Then to lift 
> >2000 # in 1 minute, 600 feet...
> >
> >you'll probably find you can use about 70% of the theoretically available 
> >power, if things work out ok.
> >
> >
> >
> >
> >
> >
> >
> >
> >
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> >
> >
> >  
> >
> >>Steve asked:
> >>
> >>    
> >>
> >>>If there is another way to do this, I don't know about it, (Hagar's
> >>>suggestion of searching the archives sounds good, but I have yet to find a
> >>>search tool to do that on this list, Is there a search utility?
> >>>      
> >>>
> >>
> >>Google is your friend. Add "vwdiesel site:www.audifans.com" (minus the 
> >>quotes) to your search phrase.
> >>
> >>I'm just about to go search for any writing about climbing hills in a 
> >>1.6 NA (82 Rabbit, 4 speed -- well, the knob says 1-2-3-E but I haven't 
> >>identified the code). I have just moved to the top of a mountain and the 
> >>last hill has an elevation increase of about 600' in just over a mile. 
> >>Hitting the bottom of the hill in 4th at 70 mph and I'm just barely able 
> >>to be doing 35 at the top with the temperature gauge about 3-4 lines 
> >>higher.) I downshift to 3rd at around 50 mph. When that starts seeming 
> >>really slow I go into 2nd for a while, but I'm not sure if I would be 
> >>better off just leaving it in 3rd.
> >>
> >>Topo map of said hill  (from the 625 at the top to the 1207 near the 
> >>middle):
> >>
> >>http://mapper.acme.com/?lat=34.540809&long=-86.257267&scale=12&theme=Topo&width=3&height=4&dot=Yes
> >>
> >>
> >>Mark
> >>
> >>(P.S. Enjoying Hagar's stories and NASA commentary -- my work email 
> >>address ends in nasa.gov).
> >>
> >>
> >>
> >>_______________________________________________
> >>Vwdiesel mailing list
> >>Vwdiesel at vwfans.com
> >>http://www.audifans.com/mailman/listinfo/vwdiesel
> >>
> >>    
> >>
> >
> >  
> >
> 
>