Dick;
To do a good analysis it would be necessary to know the length of each
wire and the current required in each wire.
Just as a "rule of thumb", look up the resistance of copper wire at 40C
(this is usually given in ohms per thousand feet). If this is divided by
1000, it gives you the resistivity in ohms per foot. Determine the
maximum current (in Amps) you will have in that wire. Then calculate the
voltage drop (V) in that wire:
V = Current x Wire Resistivity x Wire Length If this voltage drop is
more that about 0.5V, try a larger (smaller gauge) wire. The 0.5V drop
is arbitrary (taken from the old aircraft standard CAM18), but the
voltage drop should be kept to something reasonable.
The ground return is also a concern; if you run a ground return wire, it
counts into the total length calculation. A good solid connection to the
chassis is a very low resistance ground return and you can probably
assume that it is close enough to zero ohms to not worry about it. BTW,
I recommended using the 40C wire resistance rather than 25C because
copper wire resistance increases with temperature.
Regards, Neil Tucson, AZ
-----Original Message-----
From: owner-land-speed@autox.team.net
[mailto:owner-land-speed@autox.team.net] On Behalf Of Dick J
Sent: Monday, January 09, 2006 10:23 AM
To: lsr list autox
Subject: Race Car Wiring
I'm getting ready to re-wire my Firebird race car. I was surprised at
the gauge of wire leading into the HEI distributor. It looks like maybe
12 ga or even 10ga. It's pretty stout. This leads to my questions. I
will have only two circuits through switching - the ignition and the
fuel pump.
What size wire should I run from the battery to the switch panel?
What size wire should I run to the HEI?
What size wire should I run to the Holley fuel pump?
What size wire should I run from the push button to the starter
solonoid?
Is there any reason to get more complex than that - like starter
bypass, etc?
Dick J
In East Texas
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