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I would like to know if brass contacts are better, or more preferred than aluminum. Aluminum has better conductivity at 61% as opposed to brass at around 28%. However, the aluminum would most likely run hotter than brass. All replies to the above are most appreciated.
Aluminum will corrode easily, and may wear down faster (but I'm not sure about that). I do know from my experience in auto parts sales that all of the premium distributor caps and rotors use brass contacts, whereas the economy ones use aluminum.
Aluminum will corrode easily, and may wear down faster (but I'm not sure about that). I do know from my experience in auto parts sales that all of the premium distributor caps and rotors use brass contacts, whereas the economy ones use aluminum.
My car (Oldsmobile) originally was fitted with a ACDelco distributor having aluminum contacts. They say that brass lasts longer, and resists heat; which is most likely true. However, in thirty-five years of owning the same vehicle, I have experienced no heat issues, none. I'll take the aluminum which has greater conductivity: a sure spark. Thanks very much. By the way, I wonder what the racers use?
Last edited by synoptic12; Feb 4, 2022 at 05:53 PM.
I would like to know if brass contacts are better, or more preferred than aluminum. Aluminum has better conductivity at 61% as opposed to brass at around 28%.
You've asked a good question. Follow along with me as I figure out the answer.
We need to find both amperage and resistance to figure voltage loss.
At idle, an HEI spark has 60 milliamps, and it drops as rpm increases (about 30 milliamps by 3000 rpm).
We can approximate the HEI contact as a 1/4" rod, 1/2" long. That would have a cross sectional area of 10 square mm. If made of aluminum, its resistance would be 2.7 ohms per 1000 meters or 0.4 milliohms for the 1/2" length.
Brass resistivity is 3.4 times greater than aluminum, so its resistance would be 1.4 milliohms for the same length.
We can get the loss of spark voltage by multiplying amps times resistance.
So, worst-case voltage loss would be at idle. For aluminum this loss would be 60 milliamps times 0.4 milliohms = 25 microvolts (0.000025 volts).
For brass this loss would be 60 milliamps times 1.4 milliohms = 84 microvolts (0.000084 volts).
In practical terms, the voltage loss in the aluminum post would be zero, and the voltage loss in the brass post would be 3.4 times zero = zero.
So go with Kenneth's advice and experience. Choose corrosion-free brass.
You've asked a good question. Follow along with me as I figure out the answer.
We need to find both amperage and resistance to figure voltage loss.
At idle, an HEI spark has 60 milliamps, and it drops as rpm increases (about 30 milliamps by 3000 rpm).
We can approximate the HEI contact as a 1/4" rod, 1/2" long. That would have a cross sectional area of 10 square mm. If made of aluminum, its resistance would be 2.7 ohms per 1000 meters or 0.4 milliohms for the 1/2" length.
Brass resistivity is 3.4 times greater than aluminum, so its resistance would be 1.4 milliohms for the same length.
We can get the loss of spark voltage by multiplying amps times resistance.
So, worst-case voltage loss would be at idle. For aluminum this loss would be 60 milliamps times 0.4 milliohms = 25 microvolts (0.000025 volts).
For brass this loss would be 60 milliamps times 1.4 milliohms = 84 microvolts (0.000084 volts).
In practical terms, the voltage loss in the aluminum post would be zero, and the voltage loss in the brass post would be 3.4 times zero = zero.
So go with Kenneth's advice and experience. Choose corrosion-free brass.
*So, is it more efficient to have more resistance (brass) rather than conductivity (aluminum) ? "Resistivity (ρ) is an intrinsic property of a material relating to the materials resistance to the flow of electrical current. A high resistivity indicates that a material is not a good conductor of electricity."
Last edited by synoptic12; Feb 5, 2022 at 02:17 AM.
So, is it more efficient to have more resistance (brass) rather than conductivity (aluminum)?
I didn't explain effectively.
Here's another ignition system example...
Most people use spiral core spark plug wires to reduce interference with electronics (radio and ignition boxes).
Spiral core wires with best conductivity have resistance of about 50 ohms per foot. The shortest plug wire on our engines is about 18 inches, meaning it has about 75 ohms resistance.
Compare that to the resistance of the brass HEI post which has 1.4 milliohms resistance. Therefore, the short plug wire has 54,000 times the resistance of a brass HEI post.
If you shortened that plug wire by 3 ten-thousandths of an inch you would cancel the total resistance of the brass HEI post.
The bad news is that unless you make your plug wires the ABSOLUTE shortest you can, you are adding a MASSIVE amount of extra resistance to your ignition system.
The good news is that resistance doesn't matter when amperage is so low (0.06 amps).
That short plug wire drops the spark voltage by 4.5 V out of 20,000 V available.
A brass HEI post drops the spark voltage by 0.00008 V.
An aluminum HEI post would drop the spark voltage by 0.00002 V.
I ordered two ACdelco Distributor Caps and both had bent terminals and both terminals were loose. Ordered from Amazon. In addition, the terminal heads of the Dist. Cap were somewhat charred or missing. Here are some pictures. Would a loose terminal be a detriment in terms of arcing or otherwise? I really hate to use bad ignition parts when I have to perform the labor. All replies are appreciated. I may have to find another brand. Been using ACDelco for thirty-five years with no problems.
Seeking HEI Distributor Cap Info
