RE: New Track Times For V6

From: greg conner (dodgeboy93@hotmail.com)
Date: Sun Jun 03 2001 - 23:38:29 EDT


I'm shifting at like 5300 5400 or so rpms. With the stock pcm and the
limiter at 5200 i shifted at 5000...didnt seem to run as good shiftin
there...after my cam change and rr's it will be a whole new ballgame. 5400
aint safe with stock valve train.

>From: "Bernd D. Ratsch" <bernd@texas.net>
>Reply-To: dakota-truck@buffnet.net
>To: dakota-truck@buffnet.net
>Subject: RE: DML: New Track Times For V6
>Date: Sun, 03 Jun 2001 22:01:33 -0500
>
>
>I'm shifting right at 5000rpm (even with the slightly raised
>powerband)...4800rpm is just about perfect on the V6's (without cam
>changes).
>
>- Bernd
>
>-----Original Message-----
>From: owner-dakota-truck@buffnet.net
>[mailto:owner-dakota-truck@buffnet.net] On Behalf Of Bob Tom
>Sent: Sunday, June 03, 2001 8:31 PM
>To: dakota-truck@buffnet.net
>Subject: Re: DML: New Track Times For V6
>
>
>At 12:01 AM 6/4/01 +0000, you wrote:
> >i'm shifting right before red line, i don't remember rpm across the
> >line, but i shift into 3rd around 70 i think and i cross the finish
> >line around 80. Daniel
>
>Going by the factory specs for the 3.9L, red line is at 4800 rpm. So,
>let's say that you are shifting at 4700 rpm.
>
>A hp curve for a 3.9L stock engine shows that peak hp happens at about
>4200 rpm. Your peak hp rpm will depend on what mods have been done to
>your truck. Ideally, you want to cross the line near that peak hp rpm
>so that you making full use of your available power.
>
>Again, going by the stock figures that I have seen, shifting around 4700
>rpm is probably too high when you factor in the tranny and diff. gear
>ratios, i.e. the truck is decelerating (not humanly noticeable) at the
>shifts. Also, according to specs, the 3.9L peak torque happens at 3200
>rpm (yours will be different depending on mods).
>
>If you can, try and get a chasis dyno to get these rpms figures.
>
>In meantime, I would suggest the following the next time that you are at
>the track.
>
>On the first t&t run, do exactly what you have done previously with
>regards to launch and shift points but remember to see what your rpm is
>when you cross the line (write it down on your timeslip).
>
>On your next run, do the 1-2 shift at 4200 and your 2-3 at 4600. Again,
>remember to see what your rpm is crossing the line. Write these on your
>timeslip. I'm guessing at these shift points but I'm using observations
>from personal experience with regards to slippage on the shifts.
>Ideally, based on stock figures, when a shift has been completed, you
>don't want the rpm to drop below 2800-3000 when the next gear engages.
>
>Experiment from there based on your et result but change only one factor
>on the next run (just as an example, do the 1-2 at 4300 but keep the 2-3
>at 4600), and keep records of them.
>
>Basically, what I'm saying is that you need to know what you are doing
>in terms of rpms, not mph.
>
>Don't know if I need to mention this but red line rpm is an indicator of
>much you can push the engine parts without breaking and bending them.
>Usually about 300-500 rpm safety margin but don't count on it.
>
>The rpm crossing the line will provide you info. about gear ratio
>selection if you don't do any more mods. At one stage in my mods, I was
>crossing the line at 4000 rpm. I had not found a dyno shop then but
>everything that I had read and what I could feel on the track indicated
>that there was more power there i.e. I had not reached peak hp at the
>end of the 1/4. I chose to change my effective gear ratio by going to
>smaller diameter tire. It gave me 'more' track and I was now crossing
>the line at near 4500 rpm. It also got me into the 14.9s. The next
>year I put in the MPI intake manifold, found a dyno shop, and my peak hp
>was at 5000 rpm. I could not go to a even smaller tire so I change
>gears and now was crossing the line at 5000 rpm.
>
>Sorry for the length. HTH and good luck.
>Bob.
>
>

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