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Old 09-26-2007, 12:36 AM   #1
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Default Timing vocab question

When someone says that they are running 6btdc they mean thats what it is at idle....right? I mean, that will increase with RPM....right? I am wondering because i will be turboing my mspnp9495'ed miata and im going to need to get my timing right because the base map that comes with that starts at 18btdc.

Thanks in advance
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Old 09-26-2007, 01:05 AM   #2
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Quote:
Originally Posted by wes65 View Post
Thanks in advance
ha.
ha ha ha.

when they say 6 deg BTDC, it could be anywhere. usually it'll be referred to as "Base timing" when it's set (GND + TEN shorted, Idling, warmed up, etc). then advance is added or subtracted from there as RPM or load increases.
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Old 09-26-2007, 04:36 AM   #3
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the "base timing" idea does not apply when you are using megasquirt. It is only important that you synchronize the CAS and the Megasquirt before tuning. I did this by setting all the ignition tuning points near idle to 10* btdc and using a timing light, rotated the CAS until I saw 10* on the crank wheel.
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Old 09-26-2007, 08:49 AM   #4
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So, to jump in here, is it a good idea to reset timing to the stock 10 (from say, 14) when you install megasquirt?
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Old 09-26-2007, 09:14 AM   #5
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megasquirt totally controls your ignition. there's no resetting timing. you have to input the entire timing map (load vs. rpm).

the only thing you have to do is make sure MS see the exact timing it thinks it sees. meaning, once installed, you can tell MS to keep a static 10 no-matter what the situation. this give you a chance to read the timing with a light. if it doesn't show up as 10 click a few mouse buttons can correct it (trigger angle).

Once MS "sees" the correct timing. a few more mous buttons can put you at 20 at idle or 1 at idle. you have complete control to do whatever.


the best way to explain it is, the stock ecu as it's own curve. the only thing you can do is either advance or retard that entire curve. with megasquirt you generate your own curve and you advanced and retard in only the areas you seem fit.

example:

here's my timing curve...i wanted to retard timing in boost (anything over 100kPa) and retard a few degrees at my peak torque 4200RPM.

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Old 09-26-2007, 09:22 AM   #6
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Quote:
Originally Posted by wes65 View Post
When someone says that they are running 6btdc they mean thats what it is at idle....right?
For most purposes, yes. 6* BTDC (Before Top Dead Center) is the "mechanical" timing advance/retard that person is running and has set their timing to, though as Brain and others have said MS can vary the timing as you wish.
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Old 09-26-2007, 09:42 AM   #7
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to put his figures in boost into perspective this is about what the stock ecu runs with a base of 10btdc.
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And consequently what i run as well.
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Old 09-26-2007, 10:27 AM   #8
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Interesting discussion.

Braineack; why retard a few degrees at max' torque?
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Old 09-26-2007, 10:45 AM   #9
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That clears things up a lot, thanks guys. At first i thought this was going to be kind of a short answer kind of thing but thanks for taking the time to explain it!
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Old 09-26-2007, 10:47 AM   #10
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Quote:
Originally Posted by JAG View Post
Interesting discussion.

Braineack; why retard a few degrees at max' torque?

To lower my peak pressure away from TDC (later crank angle) so the knock probability is reduced.

probably dont need to but oh well, too lazy to correct.
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