Skip to main content

Could someone out there explain to me the Spark Table generated by the CB Performance Black Box.  What does it mean? what are good numbers? how is it used to improve engine performance? How do you translate the numbers into an advance slope? I am not a Windows user, would it help if I were? Is it all about vacuum?  Help.  Thank you.

Original Post

Replies sorted oldest to newest

@edsnova can certainly chime in with respect to the Black Box software and ignition tables.

Here's my take:

Centrifugal advance: start at 8-10 degrees around idle(800-950), and go up to 32(NO MORE THAN THAT) and probably 28-30 for most motors at 3000rpm. That 30 or so degrees is at WOT/full load/LOW VACUUM conditions only.

Vacuum advance: Under high vacuum conditions(and absolutely NOT at idle) you can advance another 5-12 degrees. High vacuum conditions are USUALLY light load AKA cruising(2500-4000?). Some guys bump the vacuum advance a little just off idle to eliminate that off-idle flat spot that carburetors usually have. This is due to the air changing speed just fine when the throttle opens, but the fuel being a lot heavier takes a split-second to catch up. A little off-idle advance usually fixes this.

Make your advance in smooth steps from lowest to highest value.

With advance tables you can also pull back advance at high rpm. Aircooled VW motors seem to like this: pull back advance 4 degrees per 1000rpm ABOVE 4800rpm.

I've been running this way for almost 40,000 miles since 2008. Zero problems.

Hey Rich, I don't blame you. It IS confusing.

So if you do what you just said, fire up the engine with the Black Box wired to the disty and hooked to a computer, you get a blue screen with some red numbers. Like

IMG_7335

With the engine running the RPM number will be your idle RPM. The TIMING number will show the initial timing at the RPM, so like 12 or 15.  The MAP kPA number is your vacuum reading.

When you rev the engine the RPM and timing numbers will both increase.

This initial timing map is programmed into the Black Box when you get it. There are several choices you can use, but the initial one is something like this. And you can change the number in every cell, so it doesn't matter all that much what you start with. The engine will run.

At this point you'll want to put a normal timing light on the engine and check. The timing you get with the light at idle should match perfectly what the number on the screen says. If it doesn't, you turn the disty ever so slightly until it does, then lock it down. Mine was within a degree when I first lit it up.

Now to your question. That "Timing" number corresponds to one of the numbers in one of the boxes on the grid. To see the grid, go to "edit" (top of screen, second from left) and click on "Spark Table" (which is your only choice). That brings up

IMG_7337

See the green cell, upper right? That's the one that the BB was using to set the timing when I took this picture. She was idling low right after a cold start.

See the top number there? -1.6 or something? That is the vacuum reading the box got that day with no vacuum signal plugged into it.

In other words, that was atmospheric pressure. Nothing to do with the engine at all. And so that column of numbers represented my total possible spark curve. Follow?

And if you took those numbers and plotted them in a line it would look like a spark curve for a centrifugal advance distributer like a 009. That's where I started. No vacuum at all (yet). Basically that's the column (well, that and the two just to the right of it, weather depending) which give me the timing curve at wide-open throttle. You'll notice all three sets of numbers there are the same.

After driving a few miles, I ended up tweaking the timing just a little. I reduced the timing by two degrees right around 2200 RPM to correct what I perceived as a slight knock lugging up hills. The knock went away.

The other day I got the vacuum hoses hooked up and plugged in. Here's how the spark table looked when I started the engine then

See how the green box dances around, but now over on the left side of the grid? That tells you the manifold vacuum is being read by the box, and it's using different timing values than before.

Really they aren't all that different... Max over there is now 34 before instead of 30 before.

But a few degrees' advance at low throttle is said to be good for efficiency, so now I'll drive it and start making small changes to those numbers to see how the car responds.

I was going to start Tuesday but a stuck rear caliper brought me back in after just two laps around the block.

Hope this helps. Don't hesitate to ask more questions.

Attachments

Images (2)
  • IMG_7335
  • IMG_7337

Add Reply

Post Content
×
×
×
×
Link copied to your clipboard.
×
×