Let's discuss spark advance
 

As some of you know, I recently came into a good deal on an MS3, and so I installed it into my bone stock, naturally-aspirated 1990.

For the initial base-tune, I grabbed an MSQ file from a reputable user here, visually compared the major maps (VE, ignition, etc) to those from a DIY-supplied MSPnP2 map, and judged them to be similar. So I loaded 'em up, hand-tuned the idle a bit, let TunerStudio work its magic on the VE table for a while, and wound up with a tune that's running quite well.

Except that after a tank or two of fuel, I noticed that my fuel economy seemed to be in the shitter as compared to what I'd expect.

One thing I hadn't yet touched was the spark map. I did spend some time fine-tuning the trigger latency, so I know that my actual ignition advance is the same as my commanded advance across the entire RPM range (at least, when the commanded advance is locked to 15°), and I have no reason to suspect that anything is malfunctioning there. I've also doweled the engine, and so I know that my crank pulley is aligned with the crank.

Then I remembered the thread where we were mocking TDR and their "free tuning" thread. And this letter, alleged to be from TDR to Bill Cardell at FM, concerning an analysis of some Dynotronics tunes: Letter To Flying Miata. Re: DP Tune. And FM’s Response…

Specifically, this paragraph:

6.Timing has been cut on the fuel efficiency cruising tables, this causes the car to run low timings at cruise (40’s vs 50’s) decreasing fuel economy and making the car feel slow and heavy

Now, before we go debating who is an asshat and who is not, it got me to thinking. Cruise timing in the 50s? That seems like a lot, but what if it's at least leaning in the right direction.

So here's the spark advance table that I started with, based on copy-and-paste of base tunes from reputable people:

https://www.miataturbo.net/attachmen...1&d=1353963410

Cruise timing in the 30s. The LOW 30s. So over the past few days, I've been gradually adding advance a few degrees at a time. Here's where I stand at the moment:

https://www.miataturbo.net/attachmen...1&d=1353963410

I'm not done yet, nor do I claim that this map is optimal, smooth, useful, etc. But what I do know is that the engine isn't pinging yet, and that's on craptastic 87 octane Californigas. And based entirely on the seat-of-pants dyno, I'm pretty sure that the engine is making quite a lot more power at half-to-full throttle. It's definitely climbing hills faster than it was a week ago.

What's frustrating me is that I'm having a dickens of a time finding any hard data on this topic. I've come up with tons of reference material discussing the underlying theory of ignition advance vs. BMEP, and a lot of guys disagreeing about where to set the static timing on the vacuum-advance distributors of their carbureted V8 engines, but absolutely nothing to the effect of "We put this B-series Mazda engine (or any similar 16v 4 cyl engine) on the dyno, and found that best efficiency at 3,000 RPM at 50% throttle was achieved with X amount of spark advance, and that at 100% throttle, the engine was detonation-limited to Y amount of spark advance."


Am I really the only person who is curious about this apparent dichotomy?

are you reducing fuel like crazy when you're advancing that far?

On my 9:1 engine I found that 34* of advance on 87 octane in cruise was optimal. on the 10:1 engine in 31* of advance. I tried going further and found detonation, took away fuel and detonation stayed, added fuel and detonation became more severe. I've found that I can get 34mpg at 80mph in my 10:1 engine with the headlights up on the attached MSQ.

I can't upload my VVTuner table because it's the wrong extension.

My system to determine peak fuel efficiency:

1. Place brick on throttle
2. adjust spark
3. adjust fuel
4. Does KPA raise or fall?

If I have time on the dyno on 12/15, I'm going to play with this and see what I can find. Considering my current phenomenal MPG numbers, I expect to find no improvement. I think a piston that displaced combustible air to the exhaust side of the chamber would yield a significant increase in fuel economy.

I agree with you, there is virtually no discussion of fuel economy tuning on the interweb.

I'm not sure I understand the reasoning here. Reducing fuel "like crazy" would tend to lower the detonation threshold at WOT, would it not?

I am running closed-loop across the entire map, targeting 14.7 in all conditions except the very top row, where I'm in the mid 13s. I could probably go a tad richer in that zone, though for the moment I've been concentrating mostly in the non-WOT zone, as that's where the car runs during an emissions test.

This isn't just about fuel economy, it also about torque. Although I have no dyno numbers, I do live in a very hilly area. It's quite obvious that power has been significantly improved at (and near) WOT by running roughly 10° more advance than the baseline map I started with. (Again- naturally aspirated, stock C/R, 87 octane.)

When I have a free moment, I will pull the valve cover and visually inspect the cam positioning just to be absolutely certain that it's correct, however I have no reason to suspect that it is not.

Yes, but also lengthen burn duration, creating realizing more output by approaching LPP at the given AFR and piston speed.

Hustler, how do you tune part-throttle areas with your system?

I really want more mechanical octane in my life.

Brick on the throttle then load the dyno to hit the RPM cell I want. I want to make a boat-throttle cable adapter so I can sit at the dyno computer, outside of the car and do it all there. Man, that would be so accurate.

I basically tuned cruise in my car out of boredom and it took 100x longer than it could have at the dyno.

Joe, was your bone stock car running stock ECU with EGR?

Can you compare cruise throttle angles before and after the MS3 swap? Did the throttle angle increase or decrease?

did 90's come with egr?

Ah, I see where you're going.

As I said, I'm targeting 14.7:1 in most of the map, which I ASSUME would also have been true of every one's basemaps. (Why would you want to run richer than 14.7:1 in non-WOT cruise?)

At WOT, I am running in the low to mid 13s. Depending on which textbook you believe, this is either exactly at or slightly leaner than the optimal mixture for maximum flame-front velocity. I can certainly richen the top row and see if it starts knocking. But at the moment, I can floor it at 2,000 RPM in 5th and not get any knock.

EGR was not introduced until 1994. So no, I have never had EGR on this car.

Until installing the MS3, I had neither an analog TPS nor an accurate means of logging anything. I could certainly cobble together a parallel harness to treat the MS3 as a datalogger and re-install the stock ECU if it is felt that this would yield statistically significant data, though I must admit that my desire to do that is not great.

Would you mind doing this with your original map, vs current?

aren't there OEM ecu maps floating around somewhere?

at least I thought I saw some posted some time ago. you could glance at those and get a reference point?

This is something I can probably whip together pretty easily. I will do that tonight.

Wasn't sure on EGR.

OK so I was curious because some efficiency gains can be had by running at higher throttle position for the same drive torque (which is the case with EGR--which you don't have). Pumping losses decrease relative to the work of the air/fuel charge. But you still need optimal timing to provide the best power for the fuel injected or you're just wasting part of the squirt.

Exactly.

Assuming that my target AFR must be 14.7:1, ignition advance is really the only variable that I have control over.

But this still doesn't answer the underlying question, which is why my engine seems to like more advance than most of the basemaps I am seeing for '90-'93 Miatas, given that those engines all operate under the same constraints as mine.

I was running 15.5 AFRs for economy. I haven't a clue what to do about the cruise timing. I'm paying attention, though.

It's not that simple, it's more dynamic. AFR, spark angle, and piston speed must all be considered when looking for the minimum duty cycle to sustain speed at a given MAP. For simplicity sake, keep piston speed or RPM constant and adjust AFR and spark angle to find the lowest overall PW or duty cycle. It's easy as hell to tune for power and drivability, tuning fuel economy is an art.

Mmmmm, data. Engineers like data. :D


I found a nice, secluded back road this evening and did a couple of back-to-back pulls. The road was at an upwards incline, however I was able to match speed almost exactly and use two obvious landmarks as marker points in the log.

The pulls were both done with the engine fully warmed up, and about two minutes apart from one another. I ran in third gear, holding approximately 40 MPH as indicated on the speedo. The only thing which I changed between the two pulls was the actual spark map itself, obtained by exporting a VEX from both my current MSQ and my starting MSQ, and switching between them. Ignore the listed Min and Max values in the logs, as the raw data also included accelerating up to speed, stopping and turning around at the end of the hill, etc.


The first pull, representing the "original" spark map which is common to both the MS3 MSQ I got from a user here as well as the DIYAutoTune basemap for a '90-'03 MSPnP2:

https://www.miataturbo.net/attachmen...1&d=1353984092


And the second pull, using my current spark map which is advanced roughly 8-10° in all areas relative to the first, and is by no means optimized:

https://www.miataturbo.net/attachmen...1&d=1353984092


I then took the raw log data, imported it into Microsoft Excel, trimmed it down to just the marker area, and performed an arithmetic average on all parameters of interest. In both cases, I used the last 7 seconds of data prior to the ending marker, which represented the most even section of the hill. In addition to the mean, I also computed the delta on all parameters, and the variance between min and max was approximately equal for all parameters when compared between the two logs.

For the original map, the averages are as follows:

RPM: 3250
TPS: 26.5%
MAP: 90.6 kPa
Spark: 26°
Fuel PW: 8.7ms

For my current spark map, the averages are:

RPM: 3309
TPS: 18.4%
MAP: 78.8 kPa
Spark: 37.6°
Fuel PW: 7.3ms


Pretty compelling evidence. In the second test I was actually going 1.8% faster, and yet all of the meaningful indicators are lower. TPS was 30.5% lower, MAP was 13% lower, and the most important variable, which is fuel PW, was 16.1% lower.

16% less fuel to go the same speed up the same hill, just by bumping the spark advance from 26° to 37.6°.


So the question remains: why is everyone else so retarded? (pun intended.)

Joe, I don't think these base maps you keep referencing are any sort of "standard". Most stock maps I've seen (on many different cars) run 40-45 and even 50* in cruise. Why should our little turds (that happen to love timing) be any different?

We're all retarded because we're too retarded to explore advance. LOL

Just looked at all my maps from the 2000:

I ran 40* like a boss. So maybe I wasn't that retarded:party:

Thats it, im playing with my spark map as soon as I get back from RA this weekend :party:

Just for shits and giggles, stock subaru map:
https://www.miataturbo.net/attachmen...1&d=1353987354

I noticed your little stealth edit there, Vlad. :D

Wherever I refer to a "stock" map, I am generally referencing the MSQ files which DIYAutoTune publishes for use on their DIYPnP, MSPnP2, etc. Typically, these are the files which we point people towards when they ask "where can I find a base map?"

I have judged the ignition maps in these files to be similar to the ignition maps in the MSQ files which I have seen shared by Braineack and other users here.

The mention of FM also made me curious, and so I went and downloaded their published maps for the old Link ECU (1.6, stock injectors, naturally-aspirated.) After converting them into a more useful format, I found their spark advance map to be similar to DIYs- not an exact match, but in the same general neighborhood.

Given that that you don't hear much about Miata owners re-shaping their combustion chambers, the optimal spark map (in the non-boosted area) ought to be pretty much the same for all B6 engines regardless of whatever else has been done to them. And since spark advance is quite difficult to optimize (as compared to VE, idle, etc.,), I have just always assumed that the maps provided by DIY were already optimized for a typical B6 engine in the non-boosted area. I can understand being at a bit conservative, but we're already at more than +10 degrees and still no knock, on 87 octane gasoline.

Regarding the Subaru map, that's a bit closer to what I'd have expected. I'd love to know how to convert between the MAF-based scaling of that table and something like a MAP-based scaling, but it sort of validates me theory.

I'd *really* love to see the advance table for an OEM Miata ECU. I've been searching through the infamous "Socketing" thread at Miata.net, but I have yet to find anything thus far which is in human-readable form (eg: something other than a raw hex dump with no translation.)

Joe,
What size injector are you running for that PW?

I cruise at 3700rpm at 64kpa and 5.1-5.3ms of PW on NB injectors at 80mph.

Ignore the whacked-out TPS signal, that's fixed now:
https://www.miataturbo.net/attachmen...ine=1353993466
Attachment 239792
Any more advance means detonation without fuel, and adding fuel increases PW without reducing MAP. So, I stopped here.

As I said, this engine is bone stock. Stock 1.6 injectors, cleaned and flowtested last year.



Sounds about right. You'll note that the logs I posted above were going uphill at a steady speed. Additionally, your fuel pressure is higher than mine in cruise, because you have an NB and I have an NA, so the effective flowrate is greater. So 7.3 ms for me going up a hill at 78 kPa and 5.2 ms for you at steady cruise at 64 kPa is basically the same thing.


Something is seriously wrong with your setup if you're detonation-limited to 15° at 2500 RPM at 100 kPa.

I question whether 15° in your log is actually 15° in real life.

Also, why do your log and your spark table not match? The log indicates 34° at 56 kPa at 3850 RPM. Your spark table says 31° in that region.

Reality check.

35* of intake cam advance on 87 octane with 10:1 compression. :)

I only see about 93kpa since I'm in Dallas and it's a long ways from the ocean.

I did very minor tweeking and reduced spark angle a touch and cleared out all my junk logs...that's why it doesn't match. I'll try to make a new log tomorrow on the way to work. The example was a recent adjustment where I alternated between two settings that showed good results. I went with the one that suggests .2ms shorter PW.

My 11.5:1 engine with the MSM intake cam on NA sensors (good riddance) and 93 octane:
https://www.miataturbo.net/attachmen...ine=1353995046
Don't chastize me over the lazy tune on this...it's a total Barrett Jackson tune that spits fire, bucks, and genuinely drives like shit. However, it got me to the track for M@H.

I know the topic here is primarily spark advance, but since it was spurred by unsatisfactory fuel economy... sure, you can see some improvement by tweaking the advance, but...

You can absolutely run leaner than 14.7 in cruise. Since you live in a hilly area, you need to be careful in tuning this. I'd try to map what kPa you're at at each RPM in your typical cruise modes. Say, 35-80 mph in top gear on flat ground. That is true cruise.

You should be able to EASILY set those areas to 15.5. For lower speeds (say, under 60), you can probably go leaner than that. Some people claim to have run as lean as 17-18:1.

Try setting the center of your cruise area to 15.5, taper to 14.7 by maybe 70-80 kPa, and then to your preferred richness at 100 kPa. Anything BELOW cruise MAP can taper even leaner, you won't be doing anything down there, anyway. Couple that with as much advance as you can get away with in cruise... should make a HUGE improvement in fuel economy.

Also, be sure your fuel-cut is set so that you don't use fuel anytime you're off-throttle coasting. That's a trick that all modern cars use (they call it Deceleration Fuel Cut Off) that can help a lot with economy.

There is definitely some discussion on the topic of fuel economy on the Megasquirt forums if you dig for it. Also a little bit on some of the eco-geek forums (like ecomodder.com), but those guys are more into lightness, aero and driving technique than ECU tuning.

FWIW, I've seen 48 mpg in my stock 1991 Miata. (had to "hypermile" the hell out of it to get that, but I did... hoping for 50+ once I get the MS tuned) More recently, I actually achieved 43 in city driving. (also hypermiling... but not so much that it affected how long it took me to get anywhere, or held up anybody else)

Chasing fuel economy is an interesting diversion... and generally isn't likely to get me into as much trouble as chasing speed.

Ok, so that's now two highly modified engines whose tune is irrelevant to a discussion on stock basemaps.

Thanks for playing, and enjoy your free copy of our home game.


Yes, and my last car was ultimately tuned this way. I may eventually go in that direction with this one, but for the moment I need to generate a tune that will breeze through California emissions. That means oscillating around stoich in cruise.

Assume for the moment that 14.7:1 in cruise is a given. That's how the OEM ECU operates, and it was good for around 30 MPG highway, mid to high 20s in the city. If you were to look at a complete log of my daily commute, you'd wonder if I was aware that the throttle has any possible positions other than wide-open or fully-closed. And you'll note that I am aggressively advancing the timing at 100 kPa as well, a region in which I think we can all agree that running at or leaner than stoich is generally not a good idea.

If I had a dyno in my garage, I'd be posting logs of WOT operation and comparing torque rather than fuel pulsewidth. But as all I have access to is the street, I have to go about this indirectly and assume that lower MAP and PW for a constant, partial-throttle load means higher efficiency (which I can measure directly) and will tend to translate into greater available peak torque at WOT (which I cannot directly measure.)

Given this, it's obvious that a lot of us are flailing around with grossly conservative ignition maps. I want to find out two things.

1: Why?

2: How far do we need to push the spark advance map to find the sweet spot?


I appreciate your reasoning, but fuel economy was merely a symptom which spurred my curiosity. That, in combination with a recent thread in which a third-party criticized the ignition map of a fourth-party's ECU tune, gave me a sort of Dr. House moment. Screw the patient, I'm interested in the disease.

My end-goal here is knowledge, not some arbitrary mileage number.

That said, if you'd care to share your ignition map, I'd love to see it.

I'm on a stolen ignition map at present and have done no tuning at all on my MS (just installed it a few days ago). The map I'm running is one that was dyno-tuned on a stock 1.8 making 130 rwhp, so it's worthy of consideration even though I have little experience with it. It's here: https://www.miataturbo.net/megasquir...e2/#post903093

My previous MPG-runs were done on a stock ECU (8MHz overclocked to 9MHz) and base timing set to about 16 degrees. Overclocking the ecu "stretches" the timing map, so stock timing would have come on about 10% later than stock. And I'm 6 degrees more advanced than stock... whatever that map is.

But, really, my MPG numbers are more a factor of the combination of lightness (2060#), narrow tires (175's), gearing (4.1 vs 4.3 and taller tires), aero (hard top and right mirror delete)... but mostly how I drove it. To get close to 50 mpg out of a Miata takes a lot of "momentum driving", hardcore "pulse and glide" and judicious use of engine-off neutral-coasting. Not exactly the kind of thing the typical commuter or most "normal" drivers do. I get 28-30 mpg around town without trying. (just from good habits) 30-36 on the highway depending on how fast I run.

Ending fuel economy tangent.

Good timing definitely unlocks power. My previous Miata (96R) also had an overclocked ECU, and timing advanced to 18. But, it was using a Bipes, which pulled some timing above 3500. I have a dyno chart of that setup (and comparison with the stock ECU and no Bipes) somewhere... actually, I'm sure it's in the archives of Miata.Net. I was pulling something like 118-120 hp to the wheels with a very healthy torque curve.

Ah, here is is:
Dyno - ECU Mod & Bipes - MX-5 Miata Forum

Pretty much demonstrates that bumping timing from a "typical" 14 degrees (which is already 4 degrees greater than stock) to 22 degrees can yield significant torque and power increases. The Bipes was pulling a max of 12 degrees starting at 3500.

In this instance, I'm sure some of the power increase came from decreasing the overly rich fuel mixture (12-12.5 stock) to something leaner (14ish below 4k, less than 13 until over 6500).

Based on this experimentation, if you started with a stock map, it seems that you could add 10-12 degrees below 4000, and then taper that down to near stock level from there to 7k+.

A knock sensor is on my list of things to do with the MS. I plan to do some real world "find the limits" testing and create my timing map from those results. Don't know how long it will be before I do that.

Ok, so no valid data there, either.


Yes, but there's the rub. I have utterly no idea what a "stock map" looks like under moderate load at 4,000 RPM, so I don't know what 10-12 degrees more than it would be.

That's kind of the whole point of this thread.

Interesting Thread!. Joe how are u monitoring knock/detonation?

Cheers
Scott

23 years of Miatas and nobody's cracked the stock timing map? (no, I don't have it, either... but I'm kind of surprised that it's not out there somewhere)

I was reading a thread here on MT last night where a guy mapped the "achievable" parts of the stock timing map by monitoring it through the OBDII. That seems like it could give us a good idea of what the stock map is where it matters. (I'd do it, but no OBDII)

Here it is. It's not much, but it's something.
https://www.miataturbo.net/megasquir...93/#post713985

https://www.miataturbo.net/attachmen...ine=1354007070

Pretty sure that this is the table 18psi mentioned. The load scale is next to useless however.

id think it would be safe to say 15 is max load and 0 min, perhaps guestimate 0 as 0kpa and 15 as 110kpa to allow for differnt elevations. im about to sleep but im sure someone can put taht in excell and adverage out the values in steps of 10kpa and then adverage each cell based on the ones arround it. like that smoothing spread sheet does thats about somewhere. its not 100% but it would get you pretty darn close id imagine.

The VVT engine is stock and runs only 10* of cam advance in cruise.

I think you know the answer to the 2 questions:
1) a few years ago a gt2860rs turbo was considered huge on a miata. bipes and fmu were considered satisfactory. The Link and MS1 were considered cutting edge new technology. idling and cruising @ 13:1 on pos ev1 injectors was standard. Its JUST THE WAY IT IS.
Now we got folks questioning things. Questioning tuning strategies. Setups. Etc. Figuring out more efficient ways of doing things, buying better technology.
You get the idea.
Basically: " We were too retarded to even know we were retarded "

You're among the few on here (hopefully) making strides in the right direction. Hell, I bet half the folks on here are still running FM/BEGi/DIY base maps or ones they stole/borrowed/copied from others and don't even question the values because "it runs good enough".


2) I don't think there is a set number. Esp since you're running a dinky 1.6 low comp engine. I bet you can advance it to 50* or something like that. I say test the limits til you hit det, a brick wall, or start using more fuel than normal then back off a little.

Which is most likely what you are going to do anyway.

/coffee infused morning rant

yessir. I think there's another one or two as well, but they may have been for an NB
Agreed. On all counts.

Someone like Joe can probably do that in his sleep.

In the same load/rpm my ignition map is around 29°. I was averaging around 27mpg city with rx7 460cc injectors driving 10 miles a day, 5 days a week; never getting above 50mph.

I wasalways hapy with that, and I've never tried to tune for more since I harly drive it on the highway or extended periods.

But yeah, generally speaking, as you advance spark you can reduce fuel. This is because the flame speed is reduced as you lean out, and you add advance to put the flame front back to the same spot realitevly speaking.

I think you'll be most fuel efficient if you can maintain 16.0:1 AFR with the lowest PW as determined by the spark angle.

Joe, you mentioned not having a dyno in the garage. Have you tried Virtual Dyno? It yields repeatable results which is what you need for tuning. I've been meaning to use it for spark tuning, but have been waiting for a mod that outputs the calculated torque so I can divide by MAP and smooth things out for boost variability. Given that you are NA, this would not be an issue.

I knew I had seen that stock map somewhere. Peak advance above 40 certainly suggests that our spark MAPs are overly conservative. I'm leary of directly equating the non-dimensional load numbers to pressure values though. It may not be a simple ratio conversion.


WARNING, what follows is a super-simplified spark theory 101 intended for noobs reading the thread. Worth having a few rules of thumb handy to follow the discussion.

/Begin Spark Theory 101

The objective of spark advance is to achieve peak cylinder pressure at a rotational crank position that yields best torque. The two variables are RPM and how fast the fuel burns. RPM is easy to deal with. How fast the fuel burns is affected by several factors. The main ones are:

1. What is the fuel? Some fuels are engineered to burn slowly (like AVGAS), some quickly (like race fuel).

2. What is the AFR? For gasoline, your fastest burn happens in the range of 12.5:1 to 13:1. Go richer or leaner and the burn speed slows down.

3. Charge Pressure. The higher the pressure, the faster the burn speed. That's why you retard for boost. That's why Hustler's spark maps use less advance on higher compression engines.

So what do all these variables mean? You have to tune for it and it's a PITA. Most (like me) are lazy, burn in a safe spark tune and dream about having the time and equipment to actually do it right someday. And to really do it right takes a lot more than a few full-throttle blasts on the neighborhood dyno with a "tuner."

/End Spark Theory 101.

It takes a lot more money and time then most people are willing to throw at it considering most people are averaging high 20's low 30's combined driving and that is satisfactory, especially for the turbo cars.

I feel as though to really do this right would take many many hours on a load dyno and would cost a lot of money.

Not really. You can run lots of authority on EGO with two different AFR tables (if PID EGO is set-up right) and then adjust spark and fuel to measure output with MAP constant (brick on throttle).

You can also lock wheel speed and go for the smallest duty or PW to maintain that speed, but that takes some throttle finesse and I try to eliminate as many human variables as possible. Realistically, you can fine-tune fuel in cruise in ~30minutes. You have to go in with a plan though

I was always under the impression that adding fuel reduced the flame front speed, that's why it helps starve off knock by being too rich.

More advance means you're igniting the fuel earlier, which also means you can reduce the amount of fuel, said fuel then burns faster - which doesn't matter as it's been ignited earlier.

MAx flame speed is ~12.5-13.5 AFR, flame speed is reduced everywhere else. The reason you advance spark angle with a lean AFR is to adjust cylinder pressures at the target piston speeds.

Ideally, you run a longer duration burn at low pistons speeds, shorter duration at peak piston speeds. There are other variables that affect this though, so I run static AFR targets from 0-4000rpm, 5000-7000rpm.

AFR vs. flame speed looks like this: ^

The tip is around 12.5 to 13:1. Go richer or leaner and flame speed slows. Starting from 14.7:1 and going leaner slows flame speed. Starting from 12:1 and going richer also slows flame speed.

Apparently, Hustler types faster, hence the name.

here:

https://www.miataturbo.net/attachmen...ine=1354030158

https://www.miataturbo.net/attachmen...ine=1354030158

https://www.miataturbo.net/attachmen...ine=1354030158

https://www.miataturbo.net/attachmen...ine=1354030158


that posted OEM map vs. a typical basemap you might end up with:

https://www.miataturbo.net/attachmen...1&d=1354030137

I'm guessing on the load values, but it makes sense to me. or shoudl I assume the row I marked at 60% should be 100% load? I need to find the old thread where someone was taking obdII data and populating a spark map...


but there's also a huge thing to remember.... hold on while I set it up...

Trouble with using VD to tune cruise spark is that its just as useful as looking at injector pulse width in a log afterwards. It takes a long time. If you're on a proper load varying dyno you can literally lock into a wheel speed hold the throttle so you stay in one cell, and keep hitting the +1* button in your tuning software until the torque on the dyno display plateaus (or it knocks), then back down one. Then move to the next cell. Or if you are trying to max it out, once thats done, you can lower commanded afr and add more spark while keeping the torque number the same or higher. Basically what hustler is saying.

Thanks for the clarification, makes sense :)

so while the stock timing map is intersting to look at, this is the AFR map it also follows:

https://www.miataturbo.net/attachmen...1&d=1354032455

so I mean, really, not the best point of reference... because that timing drop at 5K correlates to all that extra fuel being dumped in during open loop.

I should note that the goal is almsot always the longest duration burn, hence the awesomeness of the soft-head piston design. However without mechanical octane in that type of combustion chamber, we run a shorter duration burn at higher piston speeds because it creates more peak-dynamic cylinder pressure.

I don't have a steady-state dyno sitting in the garage. Wish I did.

For us cheapos, it would seem that a good strategy for street-tuning spark is:

1. Tune part-throttle on a long flat road at either constant MAP or constant RPM. If using constant RPM, you can tune spark for lowest PW or lowest MAP. If using constant MAP, tune for lowest PW or highest RPM.

2. Tune WOT with timed runs or something like VD. Use your part-throttle runs to make sure there is no law-enforcement present ahead of time. :D

I suspect this is a lot easier to do in W. TX than in Southern Cali or the East Coast.

I used to want to do it the cheapo way. BUT 1 speeding ticket pays for most of the dyno time you would need. AND the cheapo way takes forever, FOR-EV-ER, the dyno takes 4 hours tops and gets you better results. Oh yeah, I can road tune a car in decently in 4 hours, but I can make it perfect on the dyno in 4 hours. It'll take months to get it perfect road tuning.

I'm tuning in Rowlette on 12/15 if you want to come play, very cheap dyno time on an MD-250.

All this talk about lean AFR, rich AFR...

Rule for the thread: I am running 14.7:1 AFR in all cells except at the very top of the MAP range, and perhaps the very far end of the RPM range. Assume this to be an unchangeable constant. For the purposes of comparing to STOCK OEM IGNITION TABLES, this is the only valid scenario.


That's the big problem I'm having. I found something similar (from a 1.6) in the last page of the "Socketing" thread, and it had the disadvantage of being ambiguous on both the load and advance scales.

I don't even know if a direct, linear correlation exists between load (as computed from airflow) to MAP, much less what the conversion factor would be.



Mind sharing the ignition map?



That's quite interesting.

If I take that table at face value, it means that the OEM ECU on a '97 car is running spark advance in the high teens / low 20s at the very top, which is roughly 20° less than I have on my engine at the moment.

That's what makes me question the data.

I bumped the non-idle rows another 10% this morning, and it's still making great power with no knock.




Just added another 5% (after taking that screenshot) and we'll run that table tonight.

I think I'm going to install a table-switching switch so that I can do instant A/B comparisons between tables.

https://www.miataturbo.net/attachmen...1&d=1354037741




Two methods:

1: Turn down the radio and listen.

2: If I crack a piston in half, then I'll know I was getting knock that I couldn't hear.

Thanks for the offer. I'll definitely try to do that (assuming I've got the car back together by then). I'll PM as we get closer.

I rented some dyno time once before, specifically to tune spark, and it really didn't work out too well. First, the operator gave me a blank stare when I described what I wanted to do with spark advance. His idea was to just download maps from the internet, as if I hadn't already been doing that. Then, after a couple of runs the dyno broke down (was not communicating with the operator's laptop). Ended up wasting a day for no real gain. Whole thing kind of turned me off. Suspect things would be night and day different with a knowledgeable operator.

it pretty much mirrors the table I made out of the stock map posted in this thread that was supossedly pulled from eprom data.

both my 2.2L i4 and 2.4L i4 only put out mid-low 20° advance in cruise when I monitor on an odbII scanner.



And that thread is privvy to my awesome quote:

Yeah, you're in good hands on this deal.

37.6° is therefore closer to MBT than 26°.

Just in case nobody has stated the obvious yet, timing at MBT will yield best fuel economy. This is true whether you are running at 14.7:1, or leaner. (note that leaner will move MBT point more advanced due to slower burn).

So one can simply find MBT on the dyno for the cruise range, and be done with it.

If a given motor and octane can run at MBT at WOT, it sure as hell can run at MBT (or even past it), at part-throttle, without knocking.

As for AFR, I do believe 15.5:1 (at its MBT) cruising will yield better BSFC than 14.7:1 (at its MBT). 16:1 may start showing inefficient burning, without special swirl/tumble features in the combustion chamber.

How to find MBT at part throttle? This was my proposal. Set dyno to constant RPM mod, sweep slowly through MAP/throttle position, and plot torque vs. MAP, at various RPMs:

https://www.miataturbo.net/ecus-tuni...-can-do-46160/