Spark latency

**myburb** · 11-01-2015

I am using 6395 and 7427 OE 7.4 bins but that doesn't really affect the question which is what does everyone do about latency? Between various sbc and bbc the latency charts are all over the place yet replacement distributors and ignition modules are all the same numbers. The factory ones do have different numbers but as I said they all crossreference to the same numbers. So does that mean when ever you have a replacement dist or module your bin latency numbers are anyone's guess? I realize you could try using a timing lite with your heads just over a 5000 rpm fan but would rather not go that route so anyone got ideas? I have searched the net but it seems pretty gray.

**1project2many** · 11-01-2015

You can use a two channel scope to capture the time between the EST signal and spark. Forse the max and min advance to a set value so the timing can't change no matter the rpm then measure latency at several rpm points.

**myburb** · 11-01-2015

Thanks, I have never used an oscilloscope but will research it. I see there is some apps for tablets. I wonder if that would work and what other things would be needed.

**1project2many** · 11-01-2015

One factor to consider is how important is it to you to have the number in the software match the number at the crank. After all, the engine doesn't need to know what number the ecm is commanding to provide feedback.

I have little experience with tablets so I don't want to provide wrong advice. Some of the software I was viewing years ago for desktops was pretty good provided you had the hardware to go with it. There were a few apps that used microphone inputs that guys tried using with various degrees of success.

I suppose it would be possible to use a timing light to try and dial in latency. Like the 'scope, you'd need to set min and max max advance to prevent advance from moving. And also like the scope, you'd want to pick rpm steps to take measurements. The idea is to watch displayed advance with the light and if it's off, change the latency value in the chip. It would work best with an emulator of course for real time changes. And you aren't likely to get the same level of precision as a scope. But it would be an interesting experiment.

**myburb** · 11-05-2015

Problem solved. My burb has two timing tabs and one of them you see from below and time from the #5 cylinder. I was going thru computer store and saw $15 USB web cam and the wheels started turning. Got a block of wood and propped up the timing light and the web cam usb'd to the laptop in the cab. All work fine to see advance from cab. When I did the motor upgrade I put on a balancer with marks to 50 degrees so didn't even have to use tape. Next step is to burn a 20 chip and record at 500 rpm intervals and change latency to match the 20 degrees.