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Old 06-15-2010, 07:17 PM   #1
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Default trigger angle addition

I have had my ms1 running for about a yaer now 4 months of that on boost and frankly the tune is pretty good at this stage. However I was just poking around in settings (after having finally spent the money to get full use of t/s back) and realised two things.

1. I have trigger angle [email protected] set to +22.5

2. I have no idea why or what it is even for

Anyone want to shed any light? As I remember it the trigger angle is the base timing setting set with the timing locked asnd the timing light hooked up to make sure it is reading right. I did that in the beginning and it was/is right on the money. And the dizzy has not been moved since then. So I can only assume it is still correct.

However after a brief search on the subject I see that it is recomended that we set the addition to 0. If I was to make that change will I now have thrown the timing way off?

SO should I turn it off? or just leave it as it is since the car is running properly?

A noob question I know, but I just spotted it so go easy on me....
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Old 06-15-2010, 07:27 PM   #2
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Hang on, I meant cas not dizzy, And now that I think about it the cam cover has in fact been off recently and the cas for a new seal. I am an idiot. I'll get the light out and just reset it tomorrow. I miss tuning anyway.

Feel free to tell me why this was set to +22.5 though. I am working off of the diypnp base map (though I am now FAR from it) so that is where it must have come from.
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Old 06-15-2010, 10:04 PM   #3
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its the keep the algorithm in check. if you turn it to 0 and add 22.5* to your trigger angle number your timing will sync up again.
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Old 06-15-2010, 10:54 PM   #4
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Quote:
Originally Posted by Blaize View Post
2. I have no idea why or what it is even for
The combination of Trigger Angle and Trigger Angle Addition describe to the Megasquirt the physical relationship between the CAS and the crankshaft. Specifically, you are telling it how many degrees BTDC the crank will be at when it receives the trigger pulse (CKP) from the CAS, so it knows how many degrees of engine rotation it has to wait (as computed in microseconds) before it actually fires the ignition to achieve whatever spark advance it wants.

Put simply, the CAS needs to be set up so that it gives a trigger pulse which is further advanced (further before TDC) than the maximum possible spark advance plus the maximum dwell time. So typically, we see trigger angles of 60-70 BTDC. In essence, we tell the MS "When you see a trigger pulse, that means that the crank is at 65 BTDC (or whatever)," and from that, the MS will figure out how long to wait to fire the ignition.

Now, the reason that there are two different fields (angle and angle addition) has purely to do with some internal software constraints. The code can't deal with advance angles larger than 90, so if you find that you actual advance angle is greater than 90, you select one of the standard adders, subtract that from the actual angle, and type in the difference. So if your actual trigger advance is 100 (impossible on the Miata) you'd select an addition of +22.5, subtract 22.5 from 100 (giving you 77.5) and then enter 77.5 into Trigger Angle.

In the Miata, we typically don't need this. So we leave the addition at 0, and just enter the actual advance angle.
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Old 06-16-2010, 05:33 AM   #5
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Thanks guys. All clear now.

I think this is the most typical mt thread ever. Somone asks a dumb but at least well written question. Brain gives the short answer and J Perez explains the why. All we need now is for old hustler to tell me what he has been doing with my sister and hyper can pop over to tell me how to reroute the cas into the trunk.
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Old 06-16-2010, 10:01 AM   #6
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Quote:
Originally Posted by Blaize View Post
I think this is the most typical mt thread ever. Somone asks a dumb but at least well written question. Brain gives the short answer and J Perez explains the why. All we need now is for old hustler to tell me what he has been doing with my sister and hyper can pop over to tell me how to reroute the cas into the trunk.

Good analysis.
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Old 06-16-2010, 10:29 AM   #7
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Quote:
Originally Posted by Blaize View Post
Thanks guys. All clear now.

I think this is the most typical mt thread ever. Somone asks a dumb but at least well written question. Brain gives the short answer and J Perez explains the why. All we need now is for old hustler to tell me what he has been doing with my sister and hyper can pop over to tell me how to reroute the cas into the trunk.
lol!

Waiting for Hustler
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Old 06-16-2010, 10:48 AM   #8
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Your sister and I were making out on the couch and things were going really well, so I said "**** it" and jumped from first base to third. Well, I was pretty surprised when she pushed back and said, "Don't you think you're being a little presumptuous jumping into 3rd base so quickly?"

..."'Presumptuous'? that's a pretty big word for a 12-year old."
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Old 06-16-2010, 06:05 PM   #9
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So It turns out I was 11 deg retarded. At 11 psi that is a difference of what feels like around 20-25 hp.

Suddenly the spark map I swiped from brain is making alot more sense
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Old 06-28-2010, 04:10 AM   #10
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My Trigger angle is 64, and trig angle addition is set to 22.5.

I presume there is no disadvantage to this? And that I could just set it to 86.5 if I wanted to.

I might get the timing light out again to be sure, but there is no negative to having the addition is there?
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Old 06-28-2010, 01:34 PM   #11
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Should be same-same. As long as you verified it with a timing light when you first did the install, there should be no need to mess with it. Unless you just want to try it for your own amusement.
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