Re: Optimum shift points

["Bill Hussey" <list_squid@hotmail.com>]

>From: "Nathan" <etherwolf@sopris.net>
>Date: Wed, 16 May 2001 10:11:34 -0600
>
>I have read a lot about our cars but haven't yet found where the optimum 
>shift point is for the
>Jetta GLX. Anyone? Anyone? Bueller?

Technically speaking, every car will be slightly different ... but on this 
list, every car will be quite a bit different considering the various mods 
of engine outputs of each car.

If you really want to know the optimum shift point, it's going to take a 
little bit of research (fun research) and a dyno run.  You need the dyno run 
so you can see where your horsepower peaks, drops off, and the rate of 
decent/climb before and after the peak.

First thing you have to do is go out in your car, bring your car up to 
redline (or the rev limiter .. your choice) in first and note the exact 
speed via your spedometer.  Now shift to second, get yourself back up to 
that speed, and note what the RPMs are for that speed in 2nd gear.  Subtract 
the two numbers to get the RPM drop between 1st and 2nd gears.  Repeat this 
for the 2nd to 3rd shift, 3rd to 4th, and 4th to 5th.

Now, with dyno data in hand, figure out what the best shift point would be 
for each gear.

If you already knew how to do this, I apologize for posting it, but every 
car will be different.  Stock VR6s tend to peak a little after 5K RPM, and 
drop off quickly thereafter, so some of the later shifts (3rd-4th or 
4th-5th) may require an earlier-than-redline shift.  But the same car with a 
less restictive exhaust would produce less backpressure, bumping the power 
band a bit higher, and may now pull around peak HP levels all the way to 
redline and can/should be shifted at redline (or the rev limiter) for every 
shift.

2 things to keep into account.  On turbo'd cars, always shift as high up as 
possible to keep the turbos spinning as fast as possible while you lift off 
the throttle to complete the shift, no matter what the power curve looks 
like, keeping those turbos spooled is your primary objective.   The other 
thing to keep in mind, in 1st and sometimes 2nd gear is to keep wheelspin in 
mind.  If your car has enough power to break the front tires loose, either 
back off the throttle, or shift a few hundred RPM after they slip, but 
before they break ... wheelspin gets you nowhere.

Bill
'98 GLX
'01 325Ci in two more weeks!
_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com