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Blend of Aviation Fine Wire with Auto Plug and 9:1-1 CR

R

riobison

Well Known Member
New to me is a RV9A with 500 hrs AF and engine, O320 carb.
I’m Replacing the old ECI cylinders with the AD with new millennium cylinders and going with 9:1-1 compression ratio.

I’m running one conventional mag on the bottom plugs. As I have on hand I’m thinking of Auburn SR83P fine wire with this mag.

On the top is the Light Speed Plasma 2+ ignition
I’d like to stick with a fine wire for the auto plugs as well.

So, just wondering what the best Auto fine wire for this set up would be to match up with the aviation SR83P plugs?

Home strip is 3000 asl so density altitude is normally north of 4 to 5000+ ft Asl so the timing will probably stay at 25 deg BTC.
Certainly open to suggestions.
Thanks
Tim
 
swjohnsey said:
I run the Densos recommended by Lightspeed.
Click to expand...

+1. I have a mag and a Lightspeed Plasma III on a YIO-360-M1B (parallel valve), 8.5-1 CR. I run aviation Tempest UREM38S fine wire plugs with the mag, and the recommended Denso IK27 (#5312) auto plugs with the Plasma III. I replace the IK27's at each Condition Inspection.


Note this from the Installation and Operation Manual:

"LSE Spark Plug Gap Specifications

Engines normally timed at 25 degrees BTDC:
These are typically engines with compression ratios less than 8.7:1. Gap spark plugs fired by the CDI to .032", max wear limit is .040".

Engines normally timed at 20 degrees BTDC:
These are usually engines with compression ratios of 8.7:1 or higher. Gap spark plugs fired by the CDI to .026", max wear limit is .035"."​
 
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riobison said:
...Home strip is 3000 asl so density altitude is normally north of 4 to 5000+ ft Asl so the timing will probably stay at 25 deg BTC...
Click to expand...

Not sure I follow the above statement. Questions:

Which ignition will "stay" at 25 degrees?
Are you locking out the advance function of the LS and running fixed?
In your mind, what does Density Altitude have to do with ignition timing?
 
Hello Mike

From Light Speed CDI Manual

Engines Normally Timed at 25 degrees BTDC:
These are usually engines with compression ratios less than 8.7:1.
At idle the strobe light should indicate 40º ± 2º when the manifold pressure hose is
connected and 21º ± 2º when disconnected.

Engines Normally Timed at 20 degrees BTDC:
These are usually engines with compression ratios of 8.7:1 or higher.
The timing is retarded another 5 degrees. This setting should show idle strobe light
readings of 35º ± 2º when the manifold pressure hose is connected and 16º ± 2º
when disconnected.

Turbo and Super-Charged engines:
These settings are for turbo and super-charged engines. Turbo normalized engines
should use the above settings for engines normally timed at 20 degrees BTDC.
At idle the engine timing should be 35º ± 2º when the manifold pressure hose is
connected and 24º ± 2º when disconnected. The leading magnet(s) should be
installed 40º BTDC.

Note that these numbers are for sea level. You can add 1 degree for each
1,000 ft of density altitude. The low number (MP hose disconnected) is the
most important!

When I read this again, lol it looks like my ignition still needs to be retarded to 21 deg.

With my set up, Im interested in the mixture of Aviation and Auto plugs.

Thanks

Tim
 
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Thanks for the clarification.

Keep in mind that any ignition system that varies timing on MP does not care about the density altitude of your airport. Just like we do not adjust our idle mixture to perfection at a high altitude airport ( because then its lean for every sea level airport you visit), we want to make sure the airplane responds appropriately to the entire operational altitude block it is subject to.

The key takeaway with the LS (I presume) is understanding that the RPM based timing does not start to advance until some point after idle, so disconnecting the MP line is what determines the baseline timing. Within reason, and with the MP line open to the local atmosphere, the timing map will not begin to add the MAP advance component until you are actually at very high physical altitude when doing your timing. So in short, your base at 3000 MSL (mine is 2600, btw) probably does not even begin to trigger the MAP timing.

That said, if the LS advance schedule DOES show a significant timing addition in the range between sea level and 3000 MSL pressure, then you might be on the right track in trying to "normalize" back to the sea level baseline. However most EI advance schedules I know of are fairly conservative (or should be) in the mid 20 inch range and higher of sensed MAP. And on top of that I have found Lycomings are fairly insensitive (from a power output perspective) to optimized timing at typical TO mixtures and MAP. Based on this, I have programmed a substantial RETARD in the ignition on my Rocket in response to this behavior. My typical full power, 27 inch MAP takeoff from my 2650 MSL airport is 17 degrees advance. I do this because it buys me back a lot of detonation margin at a very small, almost unmeasurable performance cost.

To your original question about the mixture of plugs, I can only add to the experience of the many, many people who have done it before me without any apparent detriment. I have done no before/after performance testing (attributed to plugs, anyway), but my personal opinion is that when EI is involved, aviation spark plugs belong in the scrap bin, not an aircraft engine.
 
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Historically speaking, is in the past as we ran higher compression ratios, turbo charging etc. We went colder on the plugs.

Today, that doesn't seem to be as much of a concern.

That is why I brought up the question.

Thanks

Tim
 
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