Discussion On Ignition Timing - Miata Turbo Forum - Boost cars, acquire cats.

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Old 10-12-2008, 01:42 AM   #1
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Default Discussion On Ignition Timing

From what I've ever heard and read, timing shouldn't change linearly with boost. Yet most maps I see are setup linearly. For example, retard X degrees per PSI and that value for X never changes. But each degree of timing you retard does more and more. That is, each degree you retard shifts the location of maximum pressure in the cylinder further and further away from TDC. So as you get higher and higher into boost, you should actually retard less and less to keep shifting max cylinder pressure the same amount. It just seems the timing map should reflect this. But nobody does this...

Right, wrong, or dangerous, I made one of what I 'think' it should be like. It's not perfect by any means. In fact I can already see I need to redo it in some ways. But tomorrow I'm gonna put this into MS and see what happens. Granted I"m not boosted so I can't test those cells. But if anyone's brave/stupid/ignorant enough to try it I'd like to hear what you think.

Row * came from my ***. I made those numbers up by looking at a torque curve for a 1.8 and from looking at timing maps from other members on the forum. Then I put least timing at peak torque.

Row ** also came from my *** and from other members maps.
Starting from * going to **, I said "minus one" then that value minus two, then minus two, minus two, till I got to **

Star is *-17 degrees, which IMO is too retarded for a small turbo setup. But... that's the "trend" I got from looking at others maps. I think it should be more like *-14 or something for something like a 2560. Anyways, starting from Star going down, I said "minus two, that minus three, minus tree, etc".

Like I said I'm already thinking of redoing that map to make all the changes less abrupt. I might try to come up with some exponential equation to model timing as a function of boost. Any feedback's appreciated.

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Old 10-12-2008, 02:41 AM   #2
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i sorta see what you are saying, but i think there are factors not being considered like IAT. turbos start blowin hot in that top right corner.
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Old 10-12-2008, 03:00 AM   #3
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I ran something similar, albeit with much less advance up top. I was down to 9-10 degrees through about 5500 and then back up to nearly 20 by redline. I backed it down since I was worried about melting stuff; when I get an EGT probe into the MS I will crank it back up. The car pulls MUCH harder with the extra timing in there.

Edit: Added the chart. I ran this back in April. Built it on the road with the help of a very well set-up KnocksenseMS.

(Experimental spark map, use at your own risk. Don't come crying to me when you **** up your motor, I'll just laugh at you.)
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Old 10-12-2008, 12:24 PM   #4
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Quote:
Originally Posted by akaryrye View Post
i sorta see what you are saying, but i think there are factors not being considered like IAT. turbos start blowin hot in that top right
corner.
http://www.miata.net/garage/KnowYourCar/S10_Timing.html

this is a good read.
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Old 10-12-2008, 01:33 PM   #5
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I can't find a source on this, but doesn't knock resistance improve as RPM increases? that would account for the non-linear timing retard suggestions.
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Old 10-12-2008, 01:40 PM   #6
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Well I know it's a complicated matter. Total advance is a function of MANY variables:

  • AIT's
  • The faster you spin the more you have to advance just to keep the spark happening at the same phase in the engine's compression stroke.
  • Least advance at a given MAP values is at max torque which is max VE. This is when it's got the most "stuff" to burn. The more stuff, the faster the burn. So you have to retard here. But, as VE drops off, you can add advance. How much? Dunno.
  • 30 other things.
Here's the map I have above in a pretty picture. I'm going to try it out right now.

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Old 10-12-2008, 02:46 PM   #7
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Thank you Pat for this thread. This has the makings of a great one for us "mechanically challenged" Miata owners.

Thanks also to braineack for that link.

Please keep the info flowing.

I'll try to upload my current timing map to get some feedback.

Much appreciated!
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Old 10-12-2008, 02:57 PM   #8
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Hmm. It definitely runs different. If I'm cruising around 20-30 mph I barely have to touch the gas pedal at all. Kinda like I'm driving a V8 automatic Crown Vic. From a datalog I was cruising at 1575 RPMs in 5th gear, 37 kPa, and 24* advance. Idle is 26 kPa.

WOT is also different. It pulls. And the motor is "louder". It's not knocking, but it's definitely louder, mainly above 5500. And did I mention it pulls?

Take a look at this screen shot. I was running 12.5-13 :1 AFR's at WOT before this timing map. Now I'm running 14:1 ish? Weird.

At 5000 w/27 degrees total advance My AFR is 13.4 and that's with a 86 for VE in that cell.

At 5500 w/27.5 degrees total advance my AFR is 14.6 and that's with a 85 for VE in that cell.

At 7200 w/33.5 degrees total advance my AFR is 14.5 and that's with a 78 for VE in that cell.

This thing loves fuel apparently. Gonna have to redo the fuel maps it looks like cause 14:1 at WOT isn't good for power. Is anyone N/A having to run this much fuel? I guess it's the head work. I'm running 550cc injectors at 62 PSI (so there really bigger than 550's) and hitting 30.5% duty cycle with a lean engine.

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Old 10-12-2008, 02:58 PM   #9
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40degs at WOT just doesn't "sound" safe. but it will be interesting to see the results.
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Old 10-12-2008, 04:35 PM   #10
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Quote:
Originally Posted by bryantaylor View Post
40degs at WOT just doesn't "sound" safe. but it will be interesting to see the results.
I'm running close to that... at 101kPa at redline I'm at 38-39 deg. Course WOT doesn't mean much there. That's more part-throttle.

WOT represents a pretty narrow line on the average 3D map (RPM vs. MAP with spark or fuel as the cell).
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Old 10-12-2008, 06:08 PM   #11
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Quote:
Originally Posted by patsmx5 View Post
Take a look at this screen shot. I was running 12.5-13 :1 AFR's at WOT before this timing map. Now I'm running 14:1 ish? Weird.
not really, you're giving the fuel far more time to burn than before, so it's burning more completely which means there's less fuel in the air mix therefore a leaner AFR.

I've a feeling you've made a pretty big jump in timing as normal 1/2/3 deg increments don't affect the AFR's too much.

you're running a LOT more advance than I do (tho the form of FI is different, and your AIT cooling is far better than my A/W IC, I do have WI), it's still impressive you don't have any knock.

I really should re-tune my car when I get it back!
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Old 10-12-2008, 07:17 PM   #12
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Ok; I think this is my current timing map:
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Old 10-12-2008, 07:20 PM   #13
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Quote:
Originally Posted by y8s View Post
I'm running close to that... at 101kPa at redline I'm at 38-39 deg. Course WOT doesn't mean much there. That's more part-throttle.

Here's your map in plotted in a MS 12x12 map:

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Old 10-12-2008, 07:22 PM   #14
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Quote:
Originally Posted by richyvrlimited View Post
not really, you're giving the fuel far more time to burn than before, so it's burning more completely which means there's less fuel in the air mix therefore a leaner AFR.

I've a feeling you've made a pretty big jump in timing as normal 1/2/3 deg increments don't affect the AFR's too much.

you're running a LOT more advance than I do (tho the form of FI is different, and your AIT cooling is far better than my A/W IC, I do have WI), it's still impressive you don't have any knock.

I really should re-tune my car when I get it back!
Oxygen sensors look at O2, not fuel. So if the timing helped the burn be more complete that means there would be less O2, so it should read richer. I'm not sure but it reads lean now.

Also, I have NOT tested the boosted cells yet as I am turboless. If anyone N/A wants to test it I'd like to hear what happens. It should be safe for anyone N/A as the headwork I have done means I can't run as much timing as someone with the same engine and a stock head. If someone boosted wants to try it, do so at your own risk. I can email it to anyone that wants to try it. (I don't know how to host it).
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Old 10-12-2008, 07:26 PM   #15
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Stock timing on a 1.6L at WOT at redline should be 34*. A lot of us used to run 14-16* static. That would put us at 40-42* at 100kPa from 5000-7000 RPM.

I'll see if I can did up the stock timing maps... But see the link I posted above:


Code:
Table 1 Mazda MX-5 1.6 litre Timing Movements (Standard Set)

RPM 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
BTDC 10 10 12 17 22 24 28 28 31 34 36 36 36 36
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Old 10-13-2008, 10:50 AM   #16
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I made a few changes to my map, specifically adding a touch more in high rpms (where the torque drop exists) and add more to my cruise cells to match the stock timing curve. No complaints, out-of-boost drive ability has improved, pulls strong with no signs of detonation.

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Old 10-13-2008, 11:18 AM   #17
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Yeah I can't run quite as much timing as everyone else because of the head work I did. AT 5K I'm running 29 vs. your 36. I might could run more, I dunno. I'm going to try adding more timing in cruise sometime. Like you said, I saw a nice improvement in drive ability.

Take a look at your 3400 column. Your running 33 total advance at 100kPa, but then at 84 kPa it goes down? Then back to 33, then it climbs as vac increases. If you can run 33 at 100kPa without knock, you can certainly run more advance at less map. Same idea on all your columns. Advance stays the same for half the map values.
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