okay now add in your Hp and Torque curves and you got it down pat....
Shift at 6% past max hp and into the heart of your torque curve you are
going to go as fast as that motor and frontal area will allow... hp wise
and aerodynamically..... The Problem for my Camaro is that I have a really
small small motor with a ton of piston area... 4.030 bore and a stroke of
2.90... so the motor revs like snot and runs great... but when you want to
shift to forth on the big end you have to be real careful that the motor
doesn't lose it's breath so to speak by shifting to early or you will not
be in the heart of the torque curve but on the back side of it.... I.E.
stuff to much overdrive on a small motor and it will go faster and run
better in 4th then in 5thOD... Try this out on your stock 5.0 mustang and
tell me how well it does... sure the 5.0 can accelerate out of the
condition and start running up to is peak... but in my motors case it
can't...
Keith... "aren't I supposed to be packing" Turk
----------
> From: Ulix Goettsch <ulix@u.washington.edu>
> To: Daniel1312@aol.com
> Cc: spridgets@autox.team.net
> Subject: Re: Or maybe not, was Re: I'm full of $#1^... :-)
> Date: Thursday, April 29, 1999 1:58 PM
>
> Daniel,
> I don't quite follow.
> You calculate mph/rpm in 3rd and 4th gears, but how do you get to the rpm
> increase in the last line?
>
> Also, let me try to make my point logically.
> I am in 3rd gear and accelerate to 6000rpm, then I shift to 4th. The rpm
> drops. By how much does it drop is the point of discussion here.
>
> The rotational speed of output shaft of the transmission is the same
> before and after the shift, because you are going the same speed right
> before and right after the shift. Only the input shaft of the
> transmission changes speed, namely the engine rpm.
> BUT, when I rev 3rd to 6000 and then shift, the speed of the output shaft
> is the same no matter which rearend I have installed, it just translates
> to a different speed. More specifically, the output shaft is at
> 6000rpm/1.357 = 4422rpm when I am at 6000rpm in 3rd gear. This is not
> influenced by anything past the transmission. Then I shift to 4th and
> the engine rpm drops to 4422rpm.
> SO, the rpm drop from 3rd to 4th only depends on the transmission ratios,
> not anything else.
> ERGO, I think I was full of it after all :-)
>
> As an aside:
> What DOES change is the speed (mph) at which this shift occurs.
> It occurs at a higher speed for a longer diff, which means a higher load
> (through wind resistance mainly). That means that at every point in the
> rpm and gear range, the load on the engine will be higher than with the
> shorter diff. So it will take you longer to go from 4000rpm to 5000rpm
in
> 4th, but you are also going faster. I am not sure what I am trying to
> say with this. Just an observation.
>
>
> > 3.9 diff x wheel rpm = 3.9 x 911 = 3555.45
> > 3.7 diff x wheel rpm = 3.7 x 911 = 3370.70
> >
> > 3.9 diff 3555.45 divided into 60,000 = 16.875mph per 1000rpm direct
gear (4th)
> > 3.7 diff 3370.70 divided into 60,000 = 17.800mph per 1000rpm direct
gear (4th)
> >
> > 3.9 diff direct = 16.875 divided by 3rd gear (1.357) = 12.3455 mph
> > 3.7 diff direct = 17.800 divide by 3rd gear (1.357) = 13.1171mph
> >
> > rpm increase 4th to 3rd on 3.9 diff at 3000rpm = 1,101rpm
> > rpm increase 4th to 3rd on 3.7 diff at 3000rpm = 1,071rpm
> >
> > RPM increase is greater on 3.7 (taller diff) and this is why all you
guys
> > with 4.22 diffs don't worry about the wide ratios on the Jap boxes.
Fit a
> > 3.9 diff and you might think twice about the Ford box (er hum which I
happen
> > to have in my Sprite, er hum with close ratios anyway).
> >
> > Daniel1312
> >
>
> Ulix __/__,__ ___/__|__
>
.............................................(_o____o_)....<_O_____O_/...
> '67 Sprite '74 X1/9
>
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