spridgets
[Top] [All Lists]

Re: Or maybe not, was Re: I'm full of $#1^... :-)

To: Keith Turk <kturk@ala.net>
Subject: Re: Or maybe not, was Re: I'm full of $#1^... :-)
From: Ulix Goettsch <ulix@u.washington.edu>
Date: Thu, 29 Apr 1999 14:45:47 -0700 (PDT)
Cc: spridgets@autox.team.net
In-reply-to: <199904292121.QAA00155@mail.ala.net>
Reply-to: Ulix Goettsch <ulix@u.washington.edu>
Sender: owner-spridgets@autox.team.net
Keith,
I'm from Germany and back in the energy saving days, I remember reading
test on plenty of cars that would reach their Vmax in 4th rather than 5th.
5th was just too long for performance, as you describe below.

I don't know any modern cars that are still that way.
Wait, the 6-speed Corvette is one.  There probably are others after all.
My Sprite might be like that...

Ulix


On Thu, 29 Apr 1999, Keith Turk wrote:

> 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
> > 
> 

    Ulix                                       __/__,__      ___/__|__  
..............................................(_o____o_)....<_O_____O_/...
                                              '67 Sprite     '74 X1/9


<Prev in Thread] Current Thread [Next in Thread>