Okay so that link has died, but there is a new page:
Power-Off Time Delay Relayhttp://www.bowdenshobbycircuits.info/page2.htm#relay_i.gifI used the pic on the right, which uses a pot to adjust the extra time it stays open.
I'm also posting because that circuit died this year. I substituted a TIP31 for the 2n2222 and a 1n4001 for the 1n40002 diode, so I'm not sure what died exactly. I'd guess the cheap RadioShack transistor. I'm also guessing it could be the lower voltage diode I used and the big, inefficient, power-hungry CDM relay. Those fuckers get hot to the touch from it's internal coil, thats w/o current flowing through the contacts.
Anyways, the cutout still works fine when I bypass the delay circuit. I've put a few thousand miles on it and it's still working perfect. All I'd change is the stock return spring on the t-body (lower rate with more pre-load). None the less, it's fooled a couple cops so far. ;D
Edit: rebuilt the circuit, used a signal relay (11mA coil power vs 150mA for the 30A relay), and it works great. It uses a smaller cap, so the delay time is consistent.
One other thing:
I'll eventually scrap this for a better idea. Someone saw this a while back, copied it, but used a servo instead. Oddly enough I parked next to him at the King Motorsports BBQ day last year. Silver 4rd EK with a 375whp GSR. All you need is a simple PWM controller ($5 in parts), and replace the adjustable pot with 2 fixed resistors. That will give the servo only 2 possitions. I tried it with my injector cleaner PWM controller, and I got a normal RC servo (standard 60* Futaba) to move a full 90* with authority...although it was a fairly sloppy signal & jittered (it drives injectors directly).