Home Dyno (was) Datalogging RPM signal
Hugh Keir
hugh at sol.co.uk
Wed Jan 16 20:16:02 GMT 2002
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Glen,
Found this link http://members.home.net/rck/phor/06-Speed.html The =
Physics of Racing, Part 6: Speed and Horsepower =20
The article talks about many of the formulas needed - snippet follows =
below.
I am also trying to prepare a spreadsheet to calculate HP using elapsed =
time / vehicle speed.=20
The purpose being to try and link the Air / fuel ratio that gives the =
best BHP figure.
Anyone have an idea of when Steve Ciciora might start shipping the =
International orders for parts kits?
Hugh
" How big are the resistance forces, and what role does horsepower play? =
The physics of air resistance is very complex and an area of vigorous =
research today. Most of this research is done by the aerospace industry, =
which is technologically very closely related to the automobile =
industry, especially when it comes to racing. We'll slog through some =
arithmetic here to come up with a table that shows how much horsepower =
it takes to sustain speed. Those who don't have the stomach to go =
through the math can skim the next few paragraphs.=20
We cannot derive equations for air resistance here. We'll just look them =
up. My source is Fluid Mechanics, by L. D. Landau and E. M. Lifshitz, =
two eminent Russian physicists. They give the following approximate =
formula:-=20
F =3D .5 Cd A p v v=20
The factors in this equation are the following:=20
=20
Cd =3D coefficient of friction, a factor depending on the shape of a car =
and determined by experiment; for a late model Corvette it is about =
0.30;
=20
A =3D frontal area of the car; for a Corvette, it is about 20 square =
feet;=20
=20
p =3D Greek letter rho, density of air, which we calculate below;=20
=20
v =3D speed of the car.=20
Let us calculate the density of air using ``back of the envelope'' =
methods. We know that air is about 79%Nitrogen and 21%Oxygen. We can =
look up the fact that Nitrogen has a molecular weight of about 28 and =
Oxygen has a molecular weight of about 32. What is molecular weight? It =
is the mass (not the weight, despite the name) of 22.4 liters of gas. It =
is a number of historical convention, just like feet and inches, and =
doesn't have any real science behind it. So, we figure that air has an =
average molecular weight of ((79% of 28) + (21% of 32)) / 22.4 liters =
=3D 1.29 gm/l I admit to using a calculator to do this calculation, =
against the spirit of the ``back of the envelope'' style. So sue me. "
----- Original Message -----=20
From: "Glen Beard" <gbeard1 at nycap.rr.com>
To: <diy_efi at diy-efi.org>
Sent: Friday, December 21, 2001 2:30 PM
Subject: Home Dyno (was) Datalogging RPM signal
> Steve.Flanagan at VerizonWireless.com wrote:
> >=20
> > Do you have any incite as to the physics being used with that =
device.
> > What inputs are used to calculate the HP / TQ numbers? And how is =
the drag
> > from wind added to the equation.
>=20
> Here is a list of the required inputs:
> Engine type: 2/4 stoke
> Total vehicle weight
> A/M transmission and stall speed (if app)
> Axle gear ratio
> Trans gear ratio
> Tire width, aspect ratio, and diameter
> Drag coefficient
> Frontal Area
> Drivetrain loss (%)
> Ambient Temp
> Relative Humidity
> Barometric Pressure
> Elevation above sea level
>=20
> > I would love to see some of the formulas being used.
>=20
> I don't know what the formulas are, but I know I have seen
> them scattered on the web. The only ones that ever really
> gave me trouble were drag coefficient, frontal area,
> drivetrain loss, and tire diameter (because it grows from 15
> mph to 70 mph and is not accounted for). It only takes
> being off by a little to really throw your curves off.=20
> Other than that... If you don't look at the output numbers
> themselves, but instead keep everything constant and look at
> the trends, it's a fairly repeatable tool for tuning.
>=20
> --=20
> Glen Beard 95 T/A conv M6
> 355, Vortech, heads, cam...
> http://home.nycap.rr.com/gbeard1/TransAm.html
> http://home.nycap.rr.com/gbeard1/Impala/Impala.html
>=20
> ----- End of forwarded message from owner-diy_efi at diy-efi.org -----
> =
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> To unsubscribe from diy_efi, send "unsubscribe diy_efi" (without the =
quotes)
> in the body of a message (not the subject) to =
majordomo at lists.diy-efi.org
>=20
>=20
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<BODY>
<DIV><FONT face=3DVerdana size=3D2>Glen,</FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>Found this link </FONT><A=20
href=3D"http://members.home.net/rck/phor/06-Speed.html"><FONT =
face=3DVerdana=20
size=3D2>http://members.home.net/rck/phor/06-Speed.html</FONT></A><FONT=20
face=3DVerdana size=3D2> The Physics of Racing, Part 6: Speed and=20
Horsepower </FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>The article talks about many of the =
formulas=20
needed - snippet follows below.</FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>I am also trying to prepare a =
spreadsheet to=20
calculate HP using elapsed time / vehicle speed. </FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>The purpose being to try =
and link the Air /=20
fuel ratio that gives the best BHP figure.</FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>Anyone have an idea of when =
Steve=20
Ciciora might start shipping the International orders for parts=20
kits?</FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>Hugh</FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>" How big are the resistance forces, =
and what=20
role does horsepower play? The physics of air resistance is very complex =
and an=20
area of vigorous research today. Most of this research is done by the =
aerospace=20
industry, which is technologically very closely related to the =
automobile=20
industry, especially when it comes to racing. We'll slog through some =
arithmetic=20
here to come up with a table that shows how much horsepower it takes to =
sustain=20
speed. Those who don't have the stomach to go through the math can skim =
the next=20
few paragraphs. </FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>We cannot derive equations for air =
resistance=20
here. We'll just look them up. My source is Fluid Mechanics, by L. D. =
Landau and=20
E. M. Lifshitz, two eminent Russian physicists. They give the following=20
approximate formula:- </FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>F =3D .5 Cd A p v =
v </FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>The factors in this equation are the =
following:=20
</FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2> <BR>Cd =3D coefficient of =
friction, a factor=20
depending on the shape of a car and determined by experiment; for a late =
model=20
Corvette it is about 0.30;<BR> <BR>A =3D frontal area of the car; =
for a=20
Corvette, it is about 20 square feet; <BR> <BR>p =3D Greek letter =
rho,=20
density of air, which we calculate below; <BR> <BR>v =3D speed of =
the car.=20
</FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>Let us calculate the density of air =
using ``back=20
of the envelope'' methods. We know that air is about 79%Nitrogen and =
21%Oxygen.=20
We can look up the fact that Nitrogen has a molecular weight of about 28 =
and=20
Oxygen has a molecular weight of about 32. What is molecular weight? It =
is the=20
mass (not the weight, despite the name) of 22.4 liters of gas. It is a =
number of=20
historical convention, just like feet and inches, and doesn't have any =
real=20
science behind it. So, we figure that air has an average molecular =
weight=20
of ((79% of 28) + (21% of 32)) / 22.4 liters =3D 1.29 =
gm/l I=20
admit to using a calculator to do this calculation, against the spirit =
of the=20
``back of the envelope'' style. So sue me. "</FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>----- Original Message ----- =
</FONT></DIV>
<DIV>
<DIV><FONT face=3DVerdana size=3D2>From: "Glen Beard" <</FONT><A=20
href=3D"mailto:gbeard1 at nycap.rr.com"><FONT face=3DVerdana=20
size=3D2>gbeard1 at nycap.rr.com</FONT></A><FONT face=3DVerdana=20
size=3D2>></FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2>To: <</FONT><A=20
href=3D"mailto:diy_efi at diy-efi.org"><FONT face=3DVerdana=20
size=3D2>diy_efi at diy-efi.org</FONT></A><FONT face=3DVerdana =
size=3D2>></FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2>Sent: Friday, December 21, 2001 2:30=20
PM</FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2>Subject: Home Dyno (was) Datalogging =
RPM=20
signal</FONT></DIV></DIV>
<DIV><FONT face=3DVerdana><BR><FONT size=3D2></FONT></FONT></DIV><FONT =
face=3DVerdana=20
size=3D2>> </FONT><A =
href=3D"mailto:Steve.Flanagan at VerizonWireless.com"><FONT=20
face=3DVerdana =
size=3D2>Steve.Flanagan at VerizonWireless.com</FONT></A><FONT=20
face=3DVerdana size=3D2> wrote:<BR>> > <BR>> > Do you have =
any incite as=20
to the physics being used with that device.<BR>> > What inputs are =
used to=20
calculate the HP / TQ numbers? And how is the drag<BR>> > =
from wind=20
added to the equation.<BR>> <BR>> Here is a list of the required=20
inputs:<BR>> Engine type: 2/4 stoke<BR>> Total vehicle =
weight<BR>> A/M=20
transmission and stall speed (if app)<BR>> Axle gear ratio<BR>> =
Trans gear=20
ratio<BR>> Tire width, aspect ratio, and diameter<BR>> Drag=20
coefficient<BR>> Frontal Area<BR>> Drivetrain loss (%)<BR>> =
Ambient=20
Temp<BR>> Relative Humidity<BR>> Barometric Pressure<BR>> =
Elevation=20
above sea level<BR>> <BR>> > I would love to see some of the =
formulas=20
being used.<BR>> <BR>> I don't know what the formulas are, but I =
know I=20
have seen<BR>> them scattered on the web. The only ones that =
ever=20
really<BR>> gave me trouble were drag coefficient, frontal =
area,<BR>>=20
drivetrain loss, and tire diameter (because it grows from 15<BR>> mph =
to 70=20
mph and is not accounted for). It only takes<BR>> being off by =
a little=20
to really throw your curves off. <BR>> Other than that... If =
you don't=20
look at the output numbers<BR>> themselves, but instead keep =
everything=20
constant and look at<BR>> the trends, it's a fairly repeatable tool =
for=20
tuning.<BR>> <BR>> -- <BR>> Glen Beard 95 T/A conv =
M6<BR>>=20
355, Vortech, heads, cam...<BR>> </FONT><A=20
href=3D"http://home.nycap.rr.com/gbeard1/TransAm.html"><FONT =
face=3DVerdana=20
size=3D2>http://home.nycap.rr.com/gbeard1/TransAm.html</FONT></A><BR><FON=
T=20
face=3DVerdana size=3D2>> </FONT><A=20
href=3D"http://home.nycap.rr.com/gbeard1/Impala/Impala.html"><FONT =
face=3DVerdana=20
size=3D2>http://home.nycap.rr.com/gbeard1/Impala/Impala.html</FONT></A><B=
R><FONT=20
face=3DVerdana size=3D2>> <BR>> ----- End of forwarded message =
from </FONT><A=20
href=3D"mailto:owner-diy_efi at diy-efi.org"><FONT face=3DVerdana=20
size=3D2>owner-diy_efi at diy-efi.org</FONT></A><FONT face=3DVerdana =
size=3D2>=20
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