Ballast resistor

[00fxd]

My ballast resistor seeems to have almost no resistance, so I checked and it has 12v at both sides with the key on. I'm expecting it to show about 7v on the neg side. What resistance should it show?

 

[JohnZ]

At room temperature, with the wires at both ends disconnected (so you're only measuring the resistor itself), it should show between 1.0 and 2.5 ohms; you'll need a digital VOM to measure it accurately. Original specs were 0.6 ohm prior to '65 and 1.6-1.8 ohms from '65 on, but there's a lot of variabiilty, especially with the reproductions.

 

[00fxd]

Thanks again John. Yes it does show a resistance of 1.9 ohms. How should that affect the voltage to the coil? I thought the coil got a full 12 volts on the 'start' circuit, then the voltage was resisted down to 7ish volts through the resistor on the 'run' circuit to maximize point life.

 

[JohnZ]

Yes, that's correct - the coil gets a full 12 volts when cranking through the wire from the "R" terminal on the starter solenoid, and gets resistor-reduced voltage through the other wire when you're in the "run" position. You have to measure the resistor-reduced voltage at the coil (+) terminal, so there's a load applied to the resistor; a VOM doesn't provide the same load.

 

[00fxd]

So with 12v to the resistor, I'm measuring 12v on the coil side as well. There is no back feeding from any other source.
John, I've been meaning to mention, in a previous thread, some time ago, you mentioned that using a small block front sway bar with a bb rear sway bar would result in oversteer. Your dead on! I'm now on the hunt for a larger dia front sway bar. It was quite a suprise to me, considering the wimpy dia of the rear sway bar.

 

[JohnZ]

The Corvette engineers spent a lot of time and effort balancing the chassis setup for close-to-neutral handling, with terminal understeer for safety in limit-handling situations. It doesn't take much to "un-balance" that production setup, and adding a rear stabilizer bar to a car that didn't have one originally is guaranteed to upset the chassis balance (due to increased rear roll stiffness) so limit oversteer becomes a problem. Most people don't understand chassis tuning and the drastic effects minor changes can make, especially when they're only made at one end of the car; it's pretty tough to "out-engineer" the engineers when it comes to suspension development.

The aftermarket outfits that sell sway bars do their customers a great disservice by not explaining that you can't fiddle with the setup at just one end of the car without generating undesirable limit-handling results.

 

[midyear]

I noticed the same oversteer problem when I tried a larger aftermarket rear bar on my BB 67. after a year I pulled it and put the stock bar back on. car now handles better with just that itty bitty bar.

 

[Vettewine]

The Corvette engineers spent a lot of time and effort balancing the chassis setup for close-to-neutral handling, with terminal understeer for safety in limit-handling situations. It doesn't take much to "un-balance" that production setup, and adding a rear stabilizer bar to a car that didn't have one originally is guaranteed to upset the chassis balance (due to increased rear roll stiffness) so limit oversteer becomes a problem. Most people don't understand chassis tuning and the drastic effects minor changes can make, especially when they're only made at one end of the car; it's pretty tough to "out-engineer" the engineers when it comes to suspension development.

The aftermarket outfits that sell sway bars do their customers a great disservice by not explaining that you can't fiddle with the setup at just one end of the car without generating undesirable limit-handling results.

How about increasing the diameter of the front (anti)sway bar when adding a rear where none existed before? This should be OK, no? :naughty:

 

[JohnZ]

How about increasing the diameter of the front (anti)sway bar when adding a rear where none existed before? This should be OK, no? :naughty:

Yes, that's a necessity in order to maintain the chassis balance; the factory BB rear bar was always paired with a 7/8" front bar (SB was 3/4") or 15/16" with F41 springs.