EDIS iginition timing advance help please

[SidWell]

L28 block and head, N/A, MS 2.886, EDIS ignition system.

The fuel portion of my engine is pretty smooth but I am trying to figure out how to properly curve the ignition advance. The documentation is not all that clear to me. Other than using the butt dyno is there a right way to figure out how to properly advance the EDIS ignition based on RPM and MAP? Are there things NOT to do?

[cygnusx1]

What is your compression ratio? That will affect your maximum advance...

 

General rule is to be "all-in" by about 3000rpms and pull about 1.5 degrees out for every PSI boost. Can anyone correct me if I am wrong here?

[SidWell]

What is your compression ratio? That will affect your maximum advance...

 

General rule is to be "all-in" by about 3000rpms and pull about 1.5 degrees out for every PSI boost. Can anyone correct me if I am wrong here?

 

 

It is a stock block and stock compression ratio. I can burn 87 octaine without pinging.

[cygnusx1]

You can use this rule above but keep your initial and max advances conservative. I run 27initial/38max on the, lower compression, L28ET engine.

 

You may want to keep max around 30???? Wild guess.... anyone with the L28E motor have a max advance suggestion for Sidwell?

[SidWell]

Another part to the question; is the advance linear or is there a curve to it?

 

As I understand it full advance above 3K rpm. Does that change with manifold vacuum? What about at 2K rpm full throttle and 2K rpm cruising down the street, is the advance the same for both? What rate does the advance change between 1K rpm and 3K rpm at full throttle and at moderate throttle?

 

My idle MAP is 80 KPa and at wide open throttle it is 99.9 KPa. The min KPa at closed throttle deceleration is 25KPa. At freeway cruise speed my MAP is around 65KPa.

 

How does the change in MAP affect the ignition advance?

 

I have read the theory but the practical application for my motor is a little hard to extrapolate. As I understand it, advance the spark until it starts to ping and then back off a couple of degrees. That is easy to do at normal cruising speeds (65 KPa) but hard to do under full throttle acceleration. If I get it set for cruising, can I say "advance the spark 1 degree for every 10 KPa increase or decrease the spark 1 degree for every 10 KPa decrease?

Edited November 14, 2009 by SidWell
clarification

[Zmanco]

I wouldn't worry too much about the shape of the advance curve below 3k. Similar to what cygnusx1 said, I'd be all in with the advance by 3.5k. When I ran NA I was able to go as far as 35 degrees total advance, and although I don't remember where I read it, that seems to be the generally accepted max advance for our NA engines. I never dyno tuned, but I've read others say that after 30 - 35 advance there is no more power to be gained. Of course, this all assumes that you can run that much without detonation. Above you said you can run 87 octane, but you didn't say at what advance.

 

In any event, with a stock cam you can run between 12 and 20 degrees of advance at idle. I found that with a larger cam it liked more advance, and the closer to stock with the cam profile the less advance I needed. Here's the last advance curve I ran with my NA (flat top pistons, shaved P90, moderate cam, megasquirt, etc.).

[SidWell]

Zmanco... Thanks.... a bit of a sanity check is always welcome..

[BRAAP]

Sidwell,

Yes, finding each engines ideal ignition curve is a trial an error process. There is no specific curve that will work for everyone, but most curves for comparable set ups are good starting points form which to fine tune.

 

Zmanco, how much was your P-90 shaved? If not much, then I'd venture to guess there is still some power left at WOT if you bump up your total timing in that region.

 

 

Here was my EDIS-6 timing curve on the N/A race car, very mild Schiender cam, (only .465" lift), not fully dialed in and being a race car, I didn't put much effort into the part throttle region of my ignition map. At WOT, (102ish KPa) it was pretty close to ideal for this engine. I also like to set my MAP/Load scale with at least one more row above typical WOT conditions so as to cover those extraneous cold high pressure days and ram air.

 

 

Due to the L-series inefficient chamber design, N/A L-6's with stock or near stock comp ratios prefer a little more ignition advance vs. a more efficient 2 valve combustion chamber, as much as 38-42 degrees total timing at WOT for a typical near stock comp ratio N/A L-6.

[cygnusx1]

Let me join the party. Here is my latest guess.

[Zmanco]

Zmanco, how much was your P-90 shaved? If not much, then I'd venture to guess there is still some power left at WOT if you bump up your total timing in that region.

It was shaved .080" yielding 45.5 cc chambers. LEngine predicted a CR of 10.3:1 so I was detonation limited. FYI, Paul, before I built that engine you had warned about the tradeoffs of higher CR forcing less timing advance and that the opposite was the better way to go. I am now a convert!

 

Of course, I've since gone to the turbo dark side ...

 

BTW, Paul, what was the CR of that race motor?

[BRAAP]

...

Of course, I've since gone to the turbo dark side ...

 

Boost is addictive!

 

...

BTW, Paul, what was the CR of that race motor?

 

Race motor was MN47 head on L-28 OE flat top pistons, over 11:1, running slower burning Av Gas. For a stock compression N/A L-28 with good pump gas, my map is is close to the edge of max.

 

I'm still on the fence over the MN47 head with flat tops on the street, especially with pump gas! That combo has definitely proven itself to be safer than the E88, N42, zN47, etc on the flat top L-28 bottom end... Maybe the cooling passages in the head were revised?!?!?That's a discussion for another thread already in progress...