Ignition Interrupter Switch

[MCfan]

In my on-going and somewhat frustrating efforts to get my HEI set up properly for my quirky, modified 402, I have been reading everything I can get my hands on about HEI's and how to set them up for performance street applications.

 

I recently read about an "ignition interrupter switch" and how and why it is used when starting an engine with more initial advance than normal stock specifications.

 

A simple toggle switch is wired in-line with the power wire to the HEI to allow the starter to engage and get the engine turning before switching on power to the distributor/coil to fire it. The whole objective is to prevent "kickback" from plugs firing further BTDC at low starting rpms. Seemed like a simple and logical solution to a potential problem yet I don't remember ever hearing about it before, including on these forums.

 

Suddenly it dawned on me that I already had one on my car (installed by a previous owner) and I simply didn't know what it was! Duh ... I thought maybe it was just a simple theft deterrent device (like the one on my wife's Linclon Continental that cost me a hefty towing bill when my daughters accidently and unknowingly flipped it ).

 

The switch was mounted on the lower edge of the dash just above the driver's left knee and simply cut power to the original coil. It worked as a "kill switch", of course, but was a bit too obvious to be a theft deterrent IMO. I remember the timing was set at 16* initial with NO vacuum advance when I got the car. No wonder the PO complained about poor cruising mileage!

 

When I installed the HEI, I ran a new dedicated 14 ga wire from the IGN lug on my fuse panel direct to the power plug on the HEI, bypassing the original "ignition interrupter switch" in the process. A couple of terminal crimps later, I now have the switch back in operation with my HEI and it works as advertised.

 

Since I'm currently experimenting with initial advance settings in the 8* to 12* range, I'm trying to train myself to use the switch during the starting process. Although I'm not sure it is even needed for that range of intitial advance, the technique seems to provide a more consistent and reliable engine start whether cold or hot.

 

 

Just wondering how many others use an "ignition interrupter switch" and if the alleged benefits of "kickback protection" are real and worthwhile? Also, if anyone has any words of wisdom on setting up HEI's for street fun, I would love to hear them. Thanks.

[footballubet]

That's a new one for me. But people will try anything.

[Mo's70MCs]

Yeah! I see where it could have a dual function. Yet engine kickback is as early as the stater brace many people do away with in the old standard starters. Though first I've heard of an interrupter switch to intentionally kill the power to the ignition. As a kill switch & theft deterrent, a must.

[Toppless72]

Just a thought... You could eleminate the "kill switch" and power the circuit with a delay relay. It would not allow power to the HEI until the set point threshold was met. Once it had reached it's set point resistance it would close and complete the circuit allowing power to the HEI.

 

Again... Just a thought.

[7tonemonte]

Interesting, never heard of that. I like Joes idea as an alternative if you have to use one