What determines the right ignition advance?

[Jerry]

I've been thinking about using the megasquirt to control spark too, as some people here have said that it would really be worth it. I have alot of questions, and i'd hope that even some of the might get answered.

1. Is it in general more preferable to have alot or little ignition advance?

2. How does the cam shaft affect the ignition advance? For example between a T-cam and a K-cam? more or less advance? On the whole rev-range or not? on high load, low load or all load conditions?

2. How does a bigger cylinder bore affect ignition advance? more or less advance? On the whole rev-range or not? on high load, low load or all load conditions?

4. What general rules are there about ignition advance?

5. tell me more.

[kyle242gt]

Just about all you need to know Spark Timing Myths (http://www.innovatemotorsports.com/resources/myths.php) That should be enough to thoroughly confuse you.

1) It's preferable to have the right ignition advance.
2) The cam affects the cylinder fill rate and (maybe) the swirl. Cams generally need less advance where they're most efficient.
3) Bigger bore, longer distance for the flame to travel, you need more advance. But only where it doens't interact with the cam/head/etc to be a more homogenous, faster burning mixture. Confused yet?
4) Higher RPM, more advance; richer mix, less advance.
5) If it surges, it's too lean or too advanced; more advance is better with lean mixtures for cruising; you have to cut out a lot of timing in boost if you have crappy gas. I run 87.

I basically copied Kenny's 531-head map and tweaked from there. Here's what I'm running... there's still a little bit of pinging at low RPM, mid boost (7-10PSI) that I need to track down. My engine specs are in my sig.

Just because its on the same page: You Can Be Too Rich (http://www.innovatemotorsports.com/resources/rich.php)

[benflynn]

Just about all you need to know Spark Timing Myths (http://www.innovatemotorsports.com/resources/myths.php) That should be enough to thoroughly confuse you.

1) It's preferable to have the right ignition advance.
2) The cam affects the cylinder fill rate and (maybe) the swirl. Cams generally need less advance where they're most efficient.
3) Bigger bore, longer distance for the flame to travel, you need more advance. But only where it doens't interact with the cam/head/etc to be a more homogenous, faster burning mixture. Confused yet?
4) Higher RPM, more advance; richer mix, less advance.
5) If it surges, it's too lean or too advanced; more advance is better with lean mixtures for cruising; you have to cut out a lot of timing in boost if you have crappy gas. I run 87.

I basically copied Kenny's 531-head map and tweaked from there. Here's what I'm running... there's still a little bit of pinging at low RPM, mid boost (7-10PSI) that I need to track down. My engine specs are in my sig.

Just because its on the same page: You Can Be Too Rich (http://www.innovatemotorsports.com/resources/rich.php)


b21 or b230 iam running much more in boost

[linuxman51]

Ideas for timing curves:

1) start low and ramp up quickly from about 1300 to 3000 or so, and then gently increase in increments of 1-2 per 1k rpm

2) bigger bores can take more timing usually... flame front takes longer to develop

3) bigger cams take less normally but not always

4) more efficient heads take less always (and do more with less)

5) higher compression takes less most of the time

6) timing can be a crutch for a bad fuel map (or a hole in a piston)

7) the general idea is to run the least amount of timing that will still give you the power you want

8) its a fine art that you can try and cultivate or pay someone whose good at it to do for you :)

[Paul_VR6]

Holy crap 45deg advance, is this for a Hemi motor with a 5" bore? :-P Yikes. Might be no pinging, but you might make more power with less timing. Only the dyno tells that story though.

[kyle242gt]

Hey Paul-

Bearing in mind that I run 16:1 AFR at 100Kpa, lots of timing is probably a good idea. I don't start richening up until 110Kpa. I agree, though, a better idea would be some time spent on the dyno :-P I've been meaning to see if I can make a buddy's smog dyno fit the bill. :???:

I copied Kenny's map because he's smarter than I am.

I am getting more vacuum at cruise at 50* than at 37*. My goal is fuel economy at anything under about 140Kpa; If I want more power it's just a push away.

[DeathWagon]

Hey Paul-

Bearing in mind that I run 16:1 AFR at 100Kpa, lots of timing is probably a good idea. I don't start richening up until 110Kpa. I agree, though, a better idea would be some time spent on the dyno :-P I've been meaning to see if I can make a buddy's smog dyno fit the bill. :???:

I copied Kenny's map because he's smarter than I am.

I am getting more vacuum at cruise at 50* than at 37*. My goal is fuel economy at anything under about 140Kpa; If I want more power it's just a push away.


you do not need to be running it that lean at 100kpa, i wouldn't be any leaner than 14.0, you're liable to burn something up
-linux

[kyle242gt]

:omg: that's news to me. Why so? Seems if the engine's really under any kind of load, it's going to be in boost. :rant: right about the time I thought I knew something :roll:

[adrianpike]

:omg: that's news to me. Why so? Seems if the engine's really under any kind of load, it's going to be in boost. :rant: right about the time I thought I knew something :roll:

If that's true, then you're turbo is obviously too small. :-D

[kyle242gt]

shaddap you :nono: :-P

I do have a small turbo; that sumbitch spools by about 2000 RPM. My 90-110Kpa bins are at 14.0 below spool RPM.

I really don't want to cook valves or pistons; but I'm really curious why it should be richened up if it's not under load.

Besides, isn't lean = hot = fast spool?

[linuxman51]

shaddap you :nono: :-P

I do have a small turbo; that sumbitch spools by about 2000 RPM. My 90-110Kpa bins are at 14.0 below spool RPM.

I really don't want to cook valves or pistons; but I'm really curious why it should be richened up if it's not under load.

Besides, isn't lean = hot = fast spool?

mm not really, actually the fastest spool is with retarded timing and a rich condition where you get a flame front moving through the exhaust manifold

tired. maybe more later.

[ovlov760]

5) If it surges, it's too lean or too advanced; more advance is better with lean mixtures for cruising; you have to cut out a lot of timing in boost if you have crappy gas. I run 87.


What exactly do you mean by surge? If you mean surge as in pulling forward how are you to distinguish that from acceleration?

[linuxman51]

What exactly do you mean by surge? If you mean surge as in pulling forward how are you to distinguish that from acceleration?

a surge is generaly defined as something a bit violent, forwards and backwards motion. overtly lean conditions can cause it as well, but generally if you're too lean the car just rolls forward on its face and doesnt go anywhere.


also, another guideline i've been sticking to for power (and a little bit for cruise but not much), run the least timing you can to make the power you need/want to (Stealthfti).
More is not always better, and you can go too far without causing damage to things, all you're doing tho is wasting gas, as you start the flame propogation too early and develop the peak pressure too early, and not nearly as much work gets done on the piston.

[Paul_VR6]

also, another guideline i've been sticking to for power (and a little bit for cruise but not much), run the least timing you can to make the power you need/want to (Stealthfti).
More is not always better, and you can go too far without causing damage to things, all you're doing tho is wasting gas, as you start the flame propogation too early and develop the peak pressure too early, and not nearly as much work gets done on the piston.

Definitely true, and err on the less timing side of that peak by a bit (2deg). You don't want heatsoak, or a hot day ruining things easily.


I know you're trying to tune for lowest KPA for a certain RPM bin but that's HARD to do on a turbo car especially on the boost transition. The problem there is that as you change your ign timing in your current bin, the MAP will change, which puts you slightly out of where you're tuning, and you end up chasing your tail. I think that if you try and tune with a locked timing value and keep the throttle steady and just bump timing till you get a good RPM/MAP number (high vacuum), you'll be better off. That's a PAIN to to on a turbo car though, because I wouldn't want to lock a 45deg value and then accidentally spool.

Also, a good place to start is the stock WOT timing map, add 2-3deg to it for a big cam, and then add 4-5deg at part throttle. Start dropping 1deg for every lb boost at about 3-4 psi and you're making decent power, safely on almost anything.

Again, why bother 'tuning' if you don't know if you're making things better or not.

Someone come out with that ion sensing stuff so we can have an 'ignition wideband' :-P

[linuxman51]

Someone come out with that ion sensing stuff so we can have an 'ignition wideband' :-P


w3rd.

[kyle242gt]

mm not really, actually the fastest spool is with retarded timing and a rich condition where you get a flame front moving through the exhaust manifold

tired. maybe more later.

Yeah, I got that when messing with trigger angle. Thought it was really cool to be spooling at 1200 RPM in neutral. Until I read Baldur's (?) anti-lag proposal on msefi.com :yikes:

I would really appreciate more input on running lean at 100Kpa if you feel like it.

[Jerry]

Good info, i was secretly hoping that linuxman would answer. Well, anywho, tell me now that what is wrong in the following ignition chart and why? (for b21et)


............. 1000.. 1500.. 2000.. 2500.. 3000.. 3500.. 4000.. 4500.. 5000.. 5500.. 6000.. 7000..
260kPa.... 6........ 7........ 7....... 10...... 11...... 11...... 15...... 17..... 20..... 20..... 17....... 13
240kPa.... 6........ 7........ 7....... 10...... 11...... 12...... 16...... 18..... 21..... 21..... 18....... 14
220kPa.... 6........ 7........ 7....... 10...... 11...... 14...... 18...... 20..... 23..... 23..... 20....... 16
200kPa.... 6........ 7........ 7....... 10...... 13...... 16...... 20...... 22..... 25..... 25..... 22....... 18
180kPa.... 6........ 7........ 9....... 12...... 15...... 18...... 22...... 24..... 27..... 27..... 24....... 20
160kPa.... 8........ 9........ 11..... 14...... 17...... 20...... 24...... 26..... 29..... 29..... 26....... 22
140kPa.... 10...... 11...... 13...... 16...... 19...... 22...... 26...... 28..... 31..... 31..... 28....... 24
120kPa.... 11...... 12...... 15...... 18...... 21...... 24...... 28...... 30..... 33..... 33..... 30....... 26
100kPa.... 13...... 14...... 17...... 20...... 23...... 26...... 30...... 32..... 35..... 35..... 32....... 28
70kPa...... 25...... 26...... 29...... 32...... 35...... 38...... 42...... 44..... 47..... 47..... 44....... 40
40kPa...... 27...... 28...... 31...... 34...... 37...... 40...... 44...... 46..... 49..... 49..... 46....... 42
20kPa...... 27...... 28...... 31...... 34...... 37...... 40...... 44...... 46..... 49..... 49..... 46....... 42





It might only look right when the display is set to 1024*768. I don't have any way to upload images so thats the only way. Anyway, all feedback is greatly appreciated.

[Unregistered]

Well, it still doesn't look right, but if you copy it and paste it to word, it should look OK.

[kyle242gt]

Why are you pulling timing at 6000 and 7000?

I'm not sure you can even hit 260Kpa unless you change MAP sensor.

What's your engine and CR? Looks like a sh!tload of timing in high boost.

You should be able to run more timing at 100Kpa.

[benflynn]

on the msefi setup page they said more advance after 3000 rpm is not needed since the higher rpms adds enough turbulance to speed the burn rate

[kyle242gt]

wellnow then doesn't that just make a 12x12 spark map regoddamdiculous? :-P

[Jerry]

Kyle242gt: I've been told that you should have less timing on upper rpm to accomodate heat soak (if that is the correct term, english is not my native). Is that not right?



Yes, i know that mega only sees up to 1,5 bar over atmosphere. It just happened to be at 260 kpa. That map is just what i constructed based on b21et and then modded it according to some instructions i've found on the net.

There is a great possibility that it's all wrong. But i wanät to know where it goes wrong and why, because i want to learn things.


The static cr is 7,5:1 and standard squish, engine is already completeally rebuilt, so no changing those things.

But i'm also interested to hear how it would make things different with a 8,8:1 cr (for another engine).

[kyle242gt]

Can't say about heatsoak. Ben's comment re: full advance by 3000 seems a little rapid, but my map bears that out... again, though, I stole it from Kenny :love: the only real way to know is on a dyno - you'd have to get your fuel maps sorted out so you can keep the AFR constant, then do back to back runs with static timing from 3K up versus pulling a few degrees at high/higher RPM.

7.5:1 will need lots more timing than 8.8, so your map probably isn't as crazy as it looks to me with 8.7:1 and crappy crappy gasoline. My timing at 210Kpa is about 10 to 12 across the board, 12.5:1 AFR.