Which spark plug wires go where?

dwilson · #1 08-13-2006, 10:26 PM

Building an RV9a with lycoming O360 B2C. Slick mag on Left and Lightspeed on Right.
Lightspeed will fire the top plugs and mag will fire the bottom plugs.(???)

Put the cap with all the plug wires on the Slick mag today. The #1 wire is marked on the cap and there is only one way it fits, so I am assuming I did that right.

I am struggling to figure out which cylinders the other three wires go to.

Here is my thinking:
Rotation of Slick mag on the left as seen from cockpit is clockwise.
Firing order of engine is 1-3-2-4

Sooooo. The wire 1 position clockwise should go to #3 right? But that wire barely reaches if I streach it straight from the cap to the cylinder and don't route it along any reasonable routing. And the wires to 2 and 4 are very long!!!!

I could change positions of the wires on the Slick mag cap, but that seems like a BAD idea and should not be needed.

Can anyone clue me in on where my reasoning is falty?

Thanks,
Duane

dan · #2 08-13-2006, 10:30 PM

The spark plug connectors on the wires are marked, like "T1, B2, T3, B4". I didn't see that either 'til somebody pointed it out.

dwilson · #3 08-13-2006, 10:37 PM

Wow Dan,
I feel about as smart as a half spueezed rivet!!! I just went out to the garage and looked and YOU ARE RIGHT!!!!

Follow on question though, T1 means top 1 and B2 means bottom 2. But my understanding is that the lightspeed will go to all of the top plugs and the Slick to the bottom. I assume the mag doesn't really care if the T1 really goes to B1?

Thanks for your help.

Duane

dan · #4 08-13-2006, 10:40 PM

Quote:

Originally Posted by dwilson

I feel about as smart as a half spueezed rivet!!!

I know how you feel...I wasn't kidding about missing that until somebody pointed it out!

Quote:

I assume the mag doesn't really care if the T1 really goes to B1?

Not one bit. FWIW, my one Slick mag fires all bottom plugs.

Scott Will · #5 08-14-2006, 06:36 AM

Same setup as you... put T1 on B1 and T3 on B3. Fired it up for the first time yesterday and it worked like a charm. Make sure you have the Lightspeed firing the correct plugs, too. I had mine backward til a local RV'er caught it.

chuck · #6 08-14-2006, 08:58 AM

What is the purpose of changing t/b - b/t per mag/EI to t/t - b/b? Is this only done if mixing mag and EI?

dan · #7 08-14-2006, 09:02 AM

Quote:

Originally Posted by chuck

What is the purpose of changing t/b - b/t per mag/EI to t/t - b/b? Is this only done if mixing mag and EI?

Yeah. With an EI like Lightspeed, where you have coils that can mount to the top of the engine case, it's easiest to run very short wires to all top plugs...and you don't need to penetrate the baffles anywhere for plug wires (just tiny penetration(s) for the coil trigger wires...my coax splits into individual, relatively small wires prior to passing through the baffles).

It also greatly simplifies troubleshooting in a way, in case you have a bad plug or a bad wire or something.

There are those who advocate putting the "stronger" (EI) spark on the bottom plugs, since those are more likely to foul, but I personally opted for the simpler installation. EI fires all top plugs, mag fires all bottom. I have not ever, not once in 1033 hours, had a fouled plug despite the "weaker" spark firing the bottom plugs.

cytoxin · #8 08-14-2006, 03:37 PM

Quote:

Originally Posted by dan

. I have not ever, not once in 1033 hours, had a fouled plug despite the "weaker" spark firing the bottom plugs.

dan we know you dont foul plugs, how could you? i guess this is a benefit if your lop ops

Joey · #9 08-14-2006, 03:59 PM

Quote:

Originally Posted by dan

The spark plug connectors on the wires are marked, like "T1, B2, T3, B4". I didn't see that either 'til somebody pointed it out.

In my Recip Troubleshooting class in college, the professors would intentionally mix up the leads. To this day I still don't trust the markings.

hevansrv7a · #10 08-14-2006, 05:27 PM

Aside from stronger spark, the alleged advantage of the electronic ignition is control over timing. In other words, varying it for engine conditions instead of being fixed at, say, 25 deg.

OK, so under load for climb, the EI retards the spark. Meanwhile the normal mag fires - earlier - at 25, so the retardation would have very little effect. And most of your combustion is using only one plug per cylinder.

Then, you are cruising high and in thin air and LOP. You want advanced ignition but your normal mag is firing later, so you are running, again, on only one mag (the EI) and one plug for most of your combustion.

Anyone who has done a mag-drop test knows you lose about 100 rpm out of about 1700 rpm when you reduce the spark to one plug from two. Isn't it reasonable to assume this effect applies at normal cruise/climb rpm's as well?

So, how is using only one EI supposed to be a big help? I don't get it.