[Vwdiesel] Rabbit Shift Points
jhsg at sasktel.net
Tue Mar 13 11:48:47 EDT 2007
You are making one basic assumption, which seems reasonable.
You assume the upshift lights were worth a shit in the first place.
They are not.
They are dumb devices, to say, they are mechanical switches, that turn
pretty lights behind arrow shaped masks on and off.
If you want something to shift by, install a tachometer.
Roger has a very good option for those that haven't got a factory one to
go by, and his is accurate, not based on the speed of the alternator.
The speedo, as has been pointed out by Tony gives you recommended top
rpm shift points. VW speedos have had these marks going back to the
early aircooled days.
The reason the rpm changed on your shift points, is that the pump has
different timing, and has been changed, now you have a pump with
slightly different fuel settings as well (as compared to your old one).
the switches are based on the position of your foot, which controls the
angle the pump lever sits at. That angle touches or doesn't touch a
switch. Change the pump settings, it changes where your foot has to be
to get the same rpm, because power output is timing and fuel injected
quantity dependent. remount these switches on a different pump the
orientation is going to be slightly different, but the biggest change is
in timing and fueling.
To shift, use a tach, determine your best economy shift point, and shift
there. 1700-2100 is a good place for economy.
It should be noted, that since diesels vary the fuel as load varies-
(they are not slaves to a stoichiometric mix)- running at higher or
lower rpm doesn't effect fuel mileage as significantly as in a gasser.
The only added loss in higher rpm in a diesel is to pumping losses-
having to pump the extra air through the motor. Only just enough extra
fuel is used to accomplish this, whereas in a gas job, all the air that
goes through the motor must have an ideal mix (stoich) of fuel and air.
If there's no tach, you can just train your ear too. After a bit, it
works pretty good usually.
> 1. Can anybody suggest how changing the IP and its timing, could
> possibly affect when the upshift light comes on?
> 2. Can anybody tell me at what speeds the upshift light should turn
> on, with a 4 speed transmission?
> 3. My speedometer has some "dots" on its face at various speeds.
> Specifically, the face has 1 dot on it at the 23mph line. It has 2
> dots on it at the 43 mph line, and it has 3 dots on it at the 68 mph
> line. Can anybody tell me what these dots mean, if anything?
> Bryan Walton
> Vwdiesel mailing list
> Vwdiesel at vwfans.com
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