Tuning N/A engine on 87 octane: Has anyone even bothered?
 

I realize that most of you are concerned with forced induction and/or built (or heavily modified) engines, and therefor use 91 octane or greater fuel, but somewhere along the line I thought it might be a good idea to tune a base map for 87 octane. I will likely move on to 91-93 octane fuel soon, but I felt that it would be nice to finish up my 87 octane base maps and see how the car drives in comparison to the stock computer before doing so.

I worked up a rough emulation of the spark map on my 1.8 '97 using my OBD2 reader, but I had to guesstimate on a few cell blocks. I was wondering if anyone who is familiar enough with these things could take a look at my spark map and tell me if anything looks particularly troublesome? I did dial back the timing slightly in the peak areas because I've heard what I believe to be knock at times (hot humid South Texas weather) on the OBD2 computer. Does the scaling seem reasonable for a bone stock engine? I have a feeling that I could see some improvements by altering the scaling to focus more resolution on key areas rather than being so linear...

Helpful suggestions, comments, and criticism are appreciated. (Though the criticism is less appreciated than the suggestions and other comments.)

Pertinent data:
87-octane fuel
Stock 1997 Miata 1.8L OBD2 engine (only relevant modification is a coolant reroute)
MegaSquirt 1v3, parallel install
GM IAT & CLT sensors
Innovate LC-1 wideband O2 sensor (nb emulation to OBD2 computer and wideband signal to MS unit)

If thats what the stock map looks like, theres way more timing than I would have guessed.

Dann

how did you interfere between 0-100kpa and what the AFM flows for the fuel load?
I've seen various stock maps from 1.6 and 1.8s and the say on their load between 1 to 15 without indication with what the numbers refer to and without knowing what 100kpa is at what AFM flow I wasn't gonna just throw a map together like that

My method for compiling this map was to run the car entirely from the OBD2 computer and determine where the stock computer sets what timing. Using my OBD2 reader I monitored the stock ignition timing at various rpm-vs-kpa and fleshed out the chart. The MegaSquirt was not really necessary at this stage, so it was only hooked up receiving signal inputs (IAT, CLT, AFR, CPS, CKP, MAP) but not controlling anything. This made the process a little bit easier as I simply had to target the desired cell and determine the timing that the OBD2 computer was using at a given rpm-kpa and copy that value to the cell on my spark map (rather than scribble down a bunch of charts/lists and convert from inHg to kpa to put together a table).

All of the OBD2 values testing was done with the car running around CLT of 195F-205F, IAT of 96F-110F, near sea-level, and with the high humidity that we live with down here. But basically, what you see in that table are the values that the OBD2 computer spits out for the corresponding rpm-vs-kpa. The MegaSquirt was only hooked up (parallel boomslang harness sharing only 12v+ power and CKP & CMP signals) for observation during this stage.

I did not obtain any MAF readings during any of this testing, as I was not sure how relevant that data would be (since MS is using map+iat to calculate air mass, correct?) and I'm not even sure how I would go about getting the MAF readings. I did monitor the AFR of the stock computer and it seemed to stay in line with what you might expect. Hovering between 14-15 at low kpa, dipping towards 12-13 near redline at low kpa and as you approach 100kpa.

I did notice that the timing is pretty advanced at upper-mid rpms and low load, at least compared to most ignition tables that I've seen. That's basically a large part of why I posted this thread in the first place. Did I miss a key factor when working up this spark table and am I about to do something very stupid?

it looks about right from what I"ve seen on other maps
interesting though

your sparktable looks very tame to me, especially in the higher map/rpm range. I'm running about 10* average more advance than you in the same range. This is on 95 RON fuel though. No idea what that equates to for your fuels. 95 is also the lowest available commercially, so it could very well be that 87 octane is significantly worse so to speak that it warrants such a spark table.

I was a little bit conservative in the upper rpms and particularly in the peak power areas, pulling the timing back anywhere from 1 to 3 degrees compared to what the OBD2 reader was telling me, but this was done because I've had concerns about occasional knock even though I'm running 10-degrees base timing and a stock engine configuration. The hot humid weather down here can possibly be the reason for my woes, as it not only makes the air entering the engine less-than-desirable, but the humidity also gets absorbed into the gasoline more readily now that 10% ethanol is being used to achieve the specified octane.

EDIT: I just found this generalized comparison of octane ratings-
92 RON ~ 87-88 AKI
95 RON ~ 90-91 AKI
98 RON ~ 93-94 AKI

It's reassuring to hear that the table seems relatively viable. I'm not ultimately planning to stick with 87 octane, so I'm doing this is mostly just to serve as a relatively safe base map that I can drive around on for a couple of months (or less, if at all possible). But I'm wanting to use this as a way of getting comfortable with the MegaSquirt and TunerStudio before I start making any real changes/upgrades to the fueling and engine.

I did some tuning the other day and it went surprisingly smoothly, and the car was running quite well on the MegaSquirt, but I think that I could probably tweak the spark map a bit to improve stability--I think I need more resolution in a few blocks and could easily sacrifice it in other areas--and I'm sure that I still need to dial in my fuel map a bit better.

To the guy from the netherlands as OP has said in america their fuel is basically graded about 5 octane points lower for the same fuel. This is due to the way its calculated there.

To OP you will find it strange first time you tune a computer that all your AFRs are perfect but the car isnt perfectly smooth, sometimes you just have to play with the fuel cells around your hiccup and you might find they are a bit off perfect AFRs to get that part of the map nice.

Dann

Subscribed. This is wholly pertinent to my interests for the time being. Nice job Andrew!

^Same. Before I went turbo in my '93, I only ever ran 87, and tha for awhile with the timing at 16*... never missed.

My eventual '99 will be NA for some time while I do supporting mods and would love to up the stock ante. This thread will make money for people.

I am aware of the calculations being different. It's why I said 95 RON ;). I don't think that we have fuel comparable to your 87 octane availabe here. We mostly get 95 and 98, 100 is available just over te border in Germany.

In for results too. I just compiled my timing map from Hustler's and a few others that have been posted here. Tuned the fuel table (that was already close) with VE live and called it quits. You'd think I would hit the dyno and do some real tuning since I have free access at work, but whatever.

Good work.

Which cells were from actual measurements and which were interpolated?

Has anyone actually tuned 50 or 75 kPa spark timing on the dyno?

I believe americas 87 is a 93 ron equivalent.

Dann

I'm glad to hear that this is something others have interest in as well!

I had noticed some quirky behavior in a few transition areas, so I've decided to basically start fresh with a different table scaling, which I think will give me something a little more stable. I did some driveway-revving as well as some driving around under different conditions and got a better feel for which areas needed more focus. Tomorrow evening I will see if I can't start fleshing the table out a bit. Once I am able to patch together a reasonably good emulation of the stock ignition map and have a chance to verify that it's relatively close to OEM, I will post it up. Just bear in mind that it's based on a stock 1997 OBD2 1.8L engine (with California emissions, I think), so it may require some tweaking on other configurations.

In the original map that I posted, the cells in 36+24 kpa rows were pretty much all measured, but the peak ignition advance (around 4700 rpm) was pulled back from 42 to 39 (for the reasons previously mentioned). 58-44kpa from 1900 rpm and up to redline were basically measured. 80 kpa and up from 700-1900 rpm were measured. 96 kpa up to redline was measured. There seemed to be some inconsistency in transition points between a handful of cells when comparing the OBD2 readings with the MS map though, which is why I decided to start fresh with a different scale.

The other cells were more difficult to map, so they are mostly interpolation and guesswork, but I think they were pretty close.

I'm pretty interested in your findings. I have a 94 and my brother has a 94-95 motor in his 93, both megasquirted... We're going to the megameet, and I'm going to take detcans and tune the crap out of the cruise region on the 10 hour drive... He's been getting terrible mileage using the base diypnp ign map on an otherwise reasonably tuned NA car.

Timing in vacuum is almost never detonation-limited. You can advance way beyond MBT and not get ping.

Would you kindly circle or mark the cells or regions you measured?

The numbers enclosed in red boxes are the numbers that I measured with a fair amount on confidence, but I would like to re-emphasize that much of this was measured rather roughly while driving and I have not double-checked all of these cells to verify complete accuracy. The other cells were a little more difficult to nail down, so they have been interpolated and extrapolated from surrounding cells and on-the-fly readings from the OBD2 port.

For serious, I'd totally abuse free dyno time :)

I would be curious to see any results also if anyone has any. I have started working on my 1991 miata with the plan to eventually turbocharge and even though everyone says once you start you'll want more power I'm not sure (of course I haven't started yet so everyone could be correct ;)).

I plan improving to better set of wheels, brake improvements, suspension upgrades then moving on to power. I would like to install Megasquirt paired with injectors to see what could be gotten out of that combo then evaluate what my turbo needs from there.

In some ways I am trying to avoid new clutch, differential, and everything else if I don't feel I need all that power. I might well feel I need that power and at that point I guess I'll dive in but it would be nice to know what has been achieved on the way up that ladder as I suspect that most don't wake up one day and add a couple of hundred horsepower to their cars it is done in stages and I've never really seen anyone discuss at each stage what was accomplished.

Well, I've finally had some time to play with the car again. I've got a pretty decent map (I think) that covers most scenarios and seems to synch up pretty well to the OBD2. I'll probably do another test drive or two to continue monitoring it and look for inconsistencies--and fine-tune as needed--but it seems like a pretty good starting point.

I did notice that the OBD2 computer seems to be able to generate the timing value based on some different inputs though, such as being in 5th gear and letting it lug the car at idle. This situation tends to receive 0-degrees of timing when it could be getting 10-degrees at the same rpm-vs-kPa in a different gear. Anybody have some insight into this?

I also have a question for anyone who might know: When decelerating in gear while applying heavy brake, I can get the engine to pull more vacuum than usual, and once it gets into the lower RPMs I've noticed the OBD2 computer putting the timing into negative values. How important is it to try and replicate this? I think it can be done by merging a couple rows around 69kPa and adding another low-kPa row at the bottom to cover these values, but I don't know if this is something that I should really be concerned with or not?

Jason- I've also attached a copy with some of the values enclosed in red boxes. These are the values that I'm fairly confident should match with the stock OBD2 computer. The others were extrapolated and roughed-in as best as I could do with the tools and methods at hand.

can you get MAF data from the obd2 computer using your device?

Nope. Well, actually, I might be able to but I'm not sure how to. I'm just using a ScanGaugeII to display the IGN timing as a gauge output. Sadly the early OBD2 systems have pretty limited capabilities and pathetic refresh rates, which makes it challenging. I would have to do some digging to see if I could set up an xgauge to feed me data from the MAF sensor. I'm also not sure how I could use that data to my benefit for this particular project.

I had some more time to drive around and check my spark map today. It seemed pretty good but I noticed some oddity/inconsistency around the idle cells under different conditions, so I rescaled my map yet again, adjusted the low rpm cells and also tweaked it some more in other areas. The map now seems to match up to the OBD2 fairly consistently, although the OBD2 computer is a bit inconsistent in the low rpm areas across the various gears, so those values are sort of averaged out to best fit what seems to be a middle ground. Hopefully I won't be spending much time at low rpm and high load anyhow...

I will probably drive around a few more times to keep an eye on this map before I call it "ready," but I think it's getting there.

This map is definitely not as smooth as the previous map from a 3D view, but it definitely synchs up to my OBD2 readings closer than before. A smoother map may actually be more beneficial, but I figured that as close to OEM as possible is the best starting point for me. I can always smooth it out later and see if that makes things better or worse.

Now, my next question: Should the VE table be scaled the same way the spark table is scaled, or is there some reason why it might be better to scale it differently?

Jason- Areas in green I am pretty confident about. Area in red is the best compromise I felt I could get. All other areas are extrapolated from fewer data points but should be fairly appropriate.

that would be interesting to see how it works, nice info

Would you be a dear and take note of how the timing changes at idle/load when the a/c is turned on?

I use two timing maps, one with a/c activation and would like to see what the factory ECU does.

Doesn't have to be. The tables operate independently of each other.

This is part of what led me to discover that I should re-scale the table this last time. When the A/C kicks on, the kPa rises and the revs rise by about 150rpm. The timing usually surges to ~15 for a split second and then settles back down to average around 10 degrees. It seems to "hunt" a little bit more (frequently jumping between ~8 and ~13, but spending the bulk of time at 10) than with the A/C off (occasionally dips between ~7 and ~12, but spending the bulk of time around 10), but it's still essentially set at 10 degrees.

I haven't yet experimented with monitoring the timing across the board when the A/C is on though. I'll try do that next time I go out for a test session.

I know that operate independently, but I was wondering if there were any particular drawbacks or benefits by doing it one way vs. the other?

Could someone explain the -10 timing in the lower left boxes? Right now I'm running a bit higher in those boxes to help the engine catch itself if the revs fall, which makes sense to me. Why would someone want to run a negative timing here?

Those cells were filled in based on rough extrapolation from the behavior of the stock OBD2 computer on my 1997 NA. You will hopefully never see the engine in those cells as the RPMs are so low and the vacuum is extremely high, but by making the outlying values that extreme, it will (hopefully) created the desired values in the transition area between the various cells.

As the vehicle decelerates in gear (without the brakes applied) the engine will probably be somewhere around 24 kPa (could be a little higher or lower) until you get closer to idle at which point the ECU should be kicking in a bit of fuel and idle air which will raise the kPa as it approaches idle. My stock OBD2 computer set the timing in the upper RPM range very close to the values when low-load throttle was applied, then it plateaus at 28-degrees for the mid-low range and then starts dropping back towards 10 at idle. However, if you apply heavy braking while decelerating in gear it pulls more vacuum than you would normally see, at which point I was seeing timing values as low as 0-degrees during the transition from the 28-degree plateau to idle.

I'm still a supern00b when it comes to *why* the timing is set the way it is in this area, but my thinking is that you don't want advanced timing down there because (A) you're coming out of fuel-cut/overrun cells and back into idle so if something isn't right you don't want to be running lean on advanced timing, and (B) ... well, I've forgotten what B was, but I swear there was a B. It had something to do with wanting to pull timing and add fuel when under load, I think? I'm actually really tired at the moment and not totally on my game right now. (If I've made any claim that is totally stupid in this post, please disregard it. I will try to correct it tomorrow when I'm feeling a bit more refreshed.)

Less timing = more engine braking. But then, does it do this when injectors are on or off?

When in fuel over run cut, the injectors generally appear to cut back on somewhere around 1200-1500 rpm (IIRC).

jnshk
WOT up top, what is the airflow\load number at when you rev out to 7k?

I will try to check what the load % is next time I go out test driving. I have no access to airflow data at present.

For reference, all of this is being done on essentially flat ground, ~13' above sea level, ambient temps between 78-90 F, ridiculously high humidity, and after the engine has been fully engine warmed up.

Didn't have any time to do any real test driving with the MegaSquirt to verify my spark map, but I did do a couple of redline runs on my way home from work. My OBD2 reader indicated a load of ~80% for WOT from 6K to 7K in second and third gears.

thats tells me a lot of info, thanks

Is there a how-to hidden somewhere for advancing timing?

Yep, step 1 - take to reputable dyno, step 2 - success!

I do know a few old guys that live by the "advance it till it pings and back it off a notch" philosophy but that's not only dangerous but it's not the best way to make power.

Well I guess I need a reputable dyno shop in the Frederick area...

Finally had a chance to get out there and do some more test driving. The spark map seems to not be quite as tightly synchronized with the OBD2 when the AC is on full blast (as opposed to not being on at all), but it generally still follows the same readings as I get from the OBD2. So I'm thinking that my most recently posted spark map is a pretty good emulation of the OEM OBD2 for 96-97 Miatas.