At 11:45 PM 3/26/00 EST, you wrote:
> <snip>
>Anyways. I think 2 things are hurting my 1/4 miles time. 235/60/15s
instead
>of the factory 235/70/15s. I didn't use to lose traction off the line, but
>the shorter tires and "bigger" gear ratio is making me spin off the line.
If budget can handle it and depending how important 1/4-miling is to you,
drag radials will solve your traction problems off the line.
>Also down the 1/4 mile. before. as soon as I passed the finish line, it'd
>shift into 3rd. now, I shift into 3rd 7/8 of the way down the track and it
>just feels sluggish. Any ideas on that?
I would look first at what rpms your 1-2 and 2-3 shift points are. I would
get a chasis dyno, if possible, to tell you the rpms where your peak hp and
your peak torque occur. As a starting point for shift points, start testing
shifting at about 500 rpm above the peak hp rpm. Come down by 100 rpm
increments
and compare you ET times.
Also, find out what rpm you're going when your truck crosses the end line.
Compare this rpm with the dyno peak hp rpm. This will determine the type
of mods that will best suit your truck as you want the end of track rpm and
the peak hp rpm to be almost identical. If you are crossing the line at
an rpm a lot higher than the peak hp rpm, you've dropped outside your power
band and the engine is making noise and wear but gone pass its power output.
If crossing the line rpm is a lot less than peak hp rpm, then you need to
bring find mods that will raise your engine hp in that rpm gap (not a simple
thing to do).
As an example, while my experience is with an 8, I guessed, from a lot of test
run, that my peak torque was at 3300 rpm and peak hp at 4800 (turned out that
I wasn/t too far off as last Sat. dyno put them at 3200 and 4600). With
28" drag
radials, I was crossing the line at 4000 rpm. My 2-3 shift left me with only
a few hundred feet of track left resulting in a lot or power not being used.
Using the DML tire/wheel calculator, I found that 26" (235/60/15) drag radials
would have me crossing the line near 4350 rpm mark. In the real world, it
crossed
the line at 4500 rpm. The 26" tires, in effect, gave me a lot more track
to use
the power that I had in third ... cutting my ETs by almost 3/10s.
>Second thing I think is holding me back is weight. I need to get the sound
>system out and the tonneau cover off. That should drop me into the 16s.
Yep, get rid as much weight as you can ... it's free!!! More importantly,
is where you shed the weight ... front end, if possible. Shedding weight
at the rear, especially with trucks, is a tight line with gaining the benefits
from weight loss or loosing traction.
Hope this helps. Good luck.
Bob. Southern Ontario, Canada.
'97 Dakota CC Sport, FR, 5.2L, 3.55 SG, auto.
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