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Username Post: Ignition Curves        (Topic#348622)
Raven18940 
Member
Posts: 450

Reg: 09-22-04
12-09-17 02:42 PM - Post#2717422    

So after a few months of slowly soldering, I've assembled my megasquirt ECU and I'm actually ready to start wiring my TBI conversion. I'm not having any luck finding a base map, so I'm creating my own. I'm asking for some guidance on my ignition map. My car came with electronic ignition so my sticker only says set it to 0 and let the computer do the rest. Here's what I'm thinking, tell me if I'm in the ball park. This is a stock 305, so nothing aggressive is needed.

6 initial (500 RPMs)
30 total at 3500
Vacuum advance adding 5 degrees at 20".

Does that sound reasonable or am I way off? This should be a 9.5:1 car since it's equipped with a knock sensor, so I want to be on the conservative side.



 




Rick_L 
Honored Member
Posts: 27306
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
12-09-17 05:08 PM - Post#2717438    
    In response to Raven18940

That's VERY conservative unless you have high compression and run 87 octane. You'll need more of everything, and the engine will run better for it.




 
IgnitionMan 
Valued Contributor
Posts: 3290

Reg: 04-15-05
12-09-17 07:01 PM - Post#2717448    
    In response to Raven18940

I'd go with (in crankshaft degrees)

10 initial
34 total, limit 3,100 rpms
Vacuum advance to give 10, sourced for full manifold vacuum, NOT ported computation

Adjust from there

What is the EFI manufacturer's open loop timing reference degrees supposed to be set to? What EFI system are you using?



 
Raven18940 
Member
Posts: 450

Reg: 09-22-04
12-09-17 07:51 PM - Post#2717451    
    In response to IgnitionMan

  • IgnitionMan Said:
I'd go with (in crankshaft degrees)

10 initial
34 total, limit 3,100 rpms
Vacuum advance to give 10, sourced for full manifold vacuum, NOT ported computation

Adjust from there

What is the EFI manufacturer's open loop timing reference degrees supposed to be set to? What EFI system are you using?



It's a Megasquirt 3 Base, it's a build your own ECU that can use all the stock GM electronics. I'm not sure what "open loop timing reference" refers to. If I understand the terms correctly, you're talking about setting the initial timing with a light? I can literally set that number to anything I want, it's just a check box and number. Please correct me if I'm wrong.

Thanks for the timing suggestion, I'll create a map from there. That's not too much initial+vacuum advance for a LG4 305? That'll produce about 20 degrees at idle.

My plan is to fill it with 93 for the initial fire up, but eventually I want an ignition curve that will play with 87.



Edited by Raven18940 on 12-09-17 07:52 PM. Reason for edit: No reason given.

 
Shepherd 
Frequent Contributor
Posts: 1231

Loc: Lake George, NY
Reg: 11-11-15
12-10-17 07:58 AM - Post#2717472    
    In response to Raven18940

My warmed over .030 over,9.3:1 305 runs great at 15 initial and 35 @ 3k, pretty standard settings. Open loop means the o2 sensor is not controlling fuel mixture and timing, usually because it has not heated up enough to go to closed loop, this refers any Gm efi.I run 91 no ethanol with this set up.



Edited by Shepherd on 12-10-17 08:00 AM. Reason for edit: No reason given.

 
IgnitionMan 
Valued Contributor
Posts: 3290

Reg: 04-15-05
12-10-17 01:02 PM - Post#2717493    
    In response to Raven18940

By "stock electronics", I take it you mean some sort of stock GM EFI controller, modified to eliminate/lock out most of the emissions inputs, possibly modified by the guy that figured it out at GM, Bill Howell, Howell Engineering in Michigan?

And, yes, 20 degrees of timing @ IDLE, and brought back in when vacuum is high/loading is low, to none.

Ported vacuum sourcing grossly over-times engines upon acceleration, causing pinging, which we hear, and detonation that we usually do not hear.

An engine only needs ONE acceleration curve, set correctly, NOT two acceleration curves, with mechanical slowed way down to compensate for too many ported vacuum advance degrees.

Case in point, crate GMPP ZZ4 and other ZZ crate engines. GMPP demands that the vacuum advance gets plugged into ported vacuum, and to compensate for way too much acceleration timing, a dead slow mechanical curve, limiting just past 5,500 (YES, 5,500) RPM's.

Restricting the vacuum advance degrees down to 9 to 10, and connecting the vacuum advance to full manifold vacuum restores good idle, cruise, low and no load performance quality, and fitting mechanical advance springs to speed the mechanical advance back up to real world speeds stops the pinging, acceleration and engine over-heating issues.

NO reason any EFI engine can't do the same with those parameters inputted to the timing area of the fuel system.

Consider this, a timing controlled EFI uses a simple reference point, NOT initial timing, to start the timing process. The computer is going to reference all the sensors, throttle position, and ignition reference point, and compute from that reference point, and sensor inputs, either direction.



 
65_Impala 
Very Senior Member
Posts: 3991

Reg: 12-29-02
12-10-17 10:18 PM - Post#2717536    
    In response to IgnitionMan

There is no such thing as ported or manifold vacuum on EFI. EFI uses a 2 dimension table MAP vs rpm. Megasquirt is a very popular aftermarket PCM that is basically open sourced, you can build it yourself or buy in various versions from kits to complete.

As for the curve. Make the high MAP area from 80-100kPa start with about 12* up to 1000rpm then ramp up to 36* at 3000rpm then hold 36* up to the maximum rpm. Through the 0-30kPa range make a similar curve except start at about 25* and ramp up to about 48*. Make the transitions in these curves smooth and also fill in a smooth curve between these 2 areas of the table. If you detect knock, take note of the rpm and MAP where the knock occurs and pull about 4* out of the table, smooth around that area and try it again.

As for the base timing, I'd use 10*. It's rather arbitrary except that you do want the tip of the rotor to be at the plug post when firing the coil throughout the advance angles you use.



 
Raven18940 
Member
Posts: 450

Reg: 09-22-04
12-11-17 06:44 AM - Post#2717550    
    In response to IgnitionMan

IgnitionMan,

When I said stock GM electronics, I meant GM sensors. I built the computer out of component parts (using directions from someone far more experienced in electrical engineering than I).

I think you have the idea though of what I'm asking. It's just a spreadsheet with manifold pressure on one side, RPM on the other, and I'm filling in the numbers. So I have no issue with your suggested ramp rate, I'm just worried that's a bit too much advance overall.

My reasoning is thus, my engine is supposed to be 9.5:1 compression, a 175/195 cam, and it has a 195F thermostat. In theory I have fairly high dynamic compression, so I'm a little worried that 34 degrees at 3000 is too much. On the other hand I'm no expert on what a proper ignition curve for a SBC is. Maybe what you're suggesting is a conservative curve. I really have no idea, I'm just hoping that you know what you're talking about.

I suppose I should just be a little more trusting. It's not a boosted motor, it's only 165hp, I probably won't break it even with wildly wrong ignition advance. Which isn't to say what you've suggested sounds wrong, just that I'm not dealing with high stakes here.



 
IgnitionMan 
Valued Contributor
Posts: 3290

Reg: 04-15-05
12-11-17 05:16 PM - Post#2717607    
    In response to Raven18940

Odd, all the good EFI computers I have seen have provisions to set various parameters, not just a handful. But, then, I use Holley stuff, I used to work there. "megasquirt ECU", no thanks.

Go 10 initial, the computer should make it right as it reads and adjusts. The DCR won't be a problem, and, 195 deg/F., is workable for an EFI engine, even with cast iron block and heads.



 
65_Impala 
Very Senior Member
Posts: 3991

Reg: 12-29-02
12-11-17 06:54 PM - Post#2717623    
    In response to IgnitionMan

  • IgnitionMan Said:
Odd, all the good EFI computers I have seen have provisions to set various parameters, not just a handful. But, then, I use Holley stuff, I used to work there. "megasquirt ECU", no thanks.




Rather clueless response considering the Megasquirt ECU's are "only" one of the most commonly used ECU's in the aftermarket community. LOTS of tunability and very nice software.




 
Raven18940 
Member
Posts: 450

Reg: 09-22-04
12-11-17 07:37 PM - Post#2717630    
    In response to IgnitionMan

  • IgnitionMan Said:
Odd, all the good EFI computers I have seen have provisions to set various parameters, not just a handful. But, then, I use Holley stuff, I used to work there. "megasquirt ECU", no thanks.


I can set every parameter that is configurable with EFI. I can even run the torque converter lockup of my 700R4. However, I asked for an "ignition curve" because this forum tends to the old school and I thought I'd get more responses than asking for an "ignition map." I would love to run Holley stuff, but my pockets aren't that deep for this project. The MS3 ran me $400. Seriously, the Holley stuff is so awesome, it has provisions to run electronic throttles and a 4L60E.

Everything aside, thanks everyone. Your advice has been invaluable. I think I have a solid base map to start my engine. Now I just need to wire everything.



Edited by Raven18940 on 12-11-17 07:41 PM. Reason for edit: No reason given.

 
IgnitionMan 
Valued Contributor
Posts: 3290

Reg: 04-15-05
12-12-17 05:03 PM - Post#2717723    
    In response to Raven18940

"Seriously, the Holley stuff is so awesome, it has provisions to run electronic throttles and a 4L60E".

I rest my case.

I worked for Holley for 5 years, NO better EFI department head, and tech than Doug Flynn.



 
Raven18940 
Member
Posts: 450

Reg: 09-22-04
12-12-17 07:35 PM - Post#2717742    
    In response to IgnitionMan

The trouble is I want a Dominator, but only have a 4150 budget.



 
Rick_L 
Honored Member
Posts: 27306
Rick_L
Loc: Katy, Tx, USA
Reg: 07-06-00
12-12-17 07:49 PM - Post#2717744    
    In response to Raven18940

The advice given here should be able to get you a good starting place for an ignition map. You have the start and end points, a smooth curve between them will do the job.

The Megasquirt "community" should also be able to provide you similar information.

There are more sophisticated things you could do beyond this, like knock sensors and dyno tuning.

The nice thing about a computer controlled ignition map is you don't have to have that smooth curve from start to end if it's of benefit. That's where the "real" tuning comes in.



 
65_Impala 
Very Senior Member
Posts: 3991

Reg: 12-29-02
12-13-17 11:33 AM - Post#2717797    
    In response to IgnitionMan

You can run any GM engine and transmission that a Holley can operate with a Megasquirt setup instead.

Being open source, if you're smart enough you can modify the code for the Megasquirt to do anything that is not supported, or to change the functionality of a feature to suit your needs. Can't do that with a Holley.

DBW is about the only sticky part with Megasquirt, mostly because people writing code for free don't want the liability. There are a few people who have done it themselves anyways.



 
1983G20Van 
Super Senior Member
Posts: 3689

Loc: Bedford, Texas, USA
Reg: 11-13-02
12-13-17 03:14 PM - Post#2717826    
    In response to Raven18940

  • Raven18940 Said:
So after a few months of slowly soldering, I've assembled my megasquirt ECU and I'm actually ready to start wiring my TBI conversion. I'm not having any luck finding a base map, so I'm creating my own. I'm asking for some guidance on my ignition map. My car came with electronic ignition so my sticker only says set it to 0 and let the computer do the rest. Here's what I'm thinking, tell me if I'm in the ball park. This is a stock 305, so nothing aggressive is needed.

6 initial (500 RPMs)
30 total at 3500
Vacuum advance adding 5 degrees at 20".

Does that sound reasonable or am I way off? This should be a 9.5:1 car since it's equipped with a knock sensor, so I want to be on the conservative side.



I once pulled the timing advance values from a CCC Q-Jet ECM running a 305 G20 van. Used them to program into the TPI ECM as a starting point because the Camaro/Firebird timing advance table pinged horribly. The factory G20 van engine was flat top pistons with 6cc worth of valve reliefs sitting roughly .025" down the bore, 53cc 601 heads, and .020" compressed steel shim head gaskets. When you calculate the compression ratio on that, you will scratch your head!!! Cranking PSI on that setup was 210 PSI! It had a knock sensor on it too.

At 100 KPA and 1,000 rpm timing advance was 10* BTDC. 100 KPA and 2,400 rpm, timing was 20* BTDC. At 100KPA by 3,200 rpm the timing advance maxed out at 26*. I would experiment between 26 and 32* total all in between 2,800 and 3,800 rpm to figure out where it wants maximum timing. At 40 KPA and 600 rpm there was 24* of timing at idle. Cruise timing at or under 50 KPA and 3,200+ rpm was 43* BTDC. I had a LG4 305 in an Elcamino that ran best at 16* initial, 22* centrifical all in by 3,200 for 38* total timing and it had a ~10* @ 10 in/hg L82 vacuum advance on it.

1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals


Edited by 1983G20Van on 12-13-17 03:17 PM. Reason for edit: No reason given.

 
Raven18940 
Member
Posts: 450

Reg: 09-22-04
12-14-17 08:40 PM - Post#2717983    
    In response to 1983G20Van

  • 1983G20Van Said:
I once pulled the timing advance values from a CCC Q-Jet ECM running a 305 G20 van. Used them to program into the TPI ECM as a starting point because the Camaro/Firebird timing advance table pinged horribly. The factory G20 van engine was flat top pistons with 6cc worth of valve reliefs sitting roughly .025" down the bore, 53cc 601 heads, and .020" compressed steel shim head gaskets. When you calculate the compression ratio on that, you will scratch your head!!! Cranking PSI on that setup was 210 PSI! It had a knock sensor on it too.

At 100 KPA and 1,000 rpm timing advance was 10* BTDC. 100 KPA and 2,400 rpm, timing was 20* BTDC. At 100KPA by 3,200 rpm the timing advance maxed out at 26*. I would experiment between 26 and 32* total all in between 2,800 and 3,800 rpm to figure out where it wants maximum timing. At 40 KPA and 600 rpm there was 24* of timing at idle. Cruise timing at or under 50 KPA and 3,200+ rpm was 43* BTDC. I had a LG4 305 in an Elcamino that ran best at 16* initial, 22* centrifical all in by 3,200 for 38* total timing and it had a ~10* @ 10 in/hg L82 vacuum advance on it.


Thanks for the input, appreciate it.



 




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