Is my SpeedPro ignition output rising edge or falling edge?


New Member
May 27, 2001
If possible, I'd like to verify whether my SpeedPro unit's ignition output signal rising edge or falling edge.

I have what I believe is the "generic" bank-to-bank inductive box, which I use with a MSD 6A box as my ignitor. My understanding is that the MSD box triggers on rising edge input, which would make my SpeedPro setup for rising edge output. Am I correct in this assumption? Also, is this a fixed property of the hardware configuration? I'd like to know, as I may explore some different ignition options in the future.


If your interfaced to an MSD 6A ignition, It is configured for a points type output. This is an open collector type out put that switches to ground (like a coil being energized at the start of dwell period) and then released when time to fire spark. So in effect it is a rising edge output. This is the most common type of ignition drive. The ECU is configured for this output from the factory and is on a dedicated pin. Depending on exactly what you had in mind for levels and timing, the options for the spark output are somewhat broad but trivial.

I'm a bit stumped at why you would want only this output signal modified. Usually the request is for compatibilty with a particular factory ignition interface which needs compatibilty with the input and the output signals.
Thank you for the explanation, Lance. :) I'm not really interested in modifying the SpeedPro per se, but I needed to verify whether my particular unit had a rising or falling edge output. As I mentioned on this board several weeks ago, I'm thinking about trying a J&S SafeGuard knock control unit, as even with the signal attenuator circuit you posted for me a few weeks ago, I am still not getting satisfactory results from the GM ESC circuit on my Toyota -- even for SOHC engines, the Toyota 22Rx is noisy.

I have a friend-of-a-friend who has a J&S unit he isn't currently using, so I want to give it a try. I've swapped some email with John at J&S about using his unit in conjunction with the SP, and it should work fine: the unit I have is configured for a rising edge input signal, it will provide the MSD box with a rising edge output signal, so it should sit between the SP and the MSD boxes without complaint. With the J&S unit, I can retard cylinders individually or all at once, adjust input sensitivity to work with the stock Toyota knock sensor, and monitor what it's doing. (Obviously, I can't datalog the results, but otherwise I think the feature set is a good compliment to the SP.)

It can pull as much as 20° of timing out, if necessary, in one or two degree increments. Since I am still getting a handle on tuning my ignition advance table under boost, my hope is that this will give me the added margin of safety I think I need. I'm going to give it a try and see if I like it; I can always pull it back out if it doesn't do anything for me.

Anyway, thanks again for your help.

Their web site is:

Telephone: (714) 534 6975


Mailing Address: P.O.B. 2199, Garden Grove, California, 92842-2199 USA

You can read through their product descriptions on the site for more info. Their two primary products contain features that are duplicated (and better served) by features on the Speed Pro (e.g., boost retard), but they will make up a cheaper version that's dedicated to just knock control if you ask them.


>I am still not getting satisfactory results from the GM ESC circuit on my Toyota -- even for SOHC engines, the Toyota 22Rx is noisy.

Well try out the J&S but again, keep in mind that if there's alot of acoustic noise at the knock frequency there's nothing you can do really to fix that situation, at least with a basic aproach :) You can attenuate the input but it will also attenuate the desired signal along with it too, so the net result is probably no improvement in the signal/noise ratio. You can probably get the box to be quiet whilke cruising but then you won't know for sure if it's still able to detect real knock or not. It's not an easy job. Just FWIW.