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 :)