Jason, thats pretty much what we're saying already I just dont think anyone said MBT. Its certainly what I was talking about, there should be no need for a plot of torque vs map. Mainly because thats a really damn hard plot to make since the dyno wont know the map and your ecu wont know what they dyno is reading, so you'll have to make the plot externally assuming you can even get the dyno to output the data in a format thats easy to manipulate. Its much easier to look at what cell you're in and look at the live dyno output and keep adding timing until torque stops increasing.

Yes, Jason enjoys cluttering up my threads by re-stating the obvious and attempting to divert them away from the principle topic.

Of course, getting onto a dyno and optimizing my ignition map would be fairly easy (if I could find a load-bearing dyno around here- this is DynoJet country apparently.) Doing so, however, would not answer my underlying question vis-a-vis why we all seem to be stuck in this habit of using grossly sub-optimal spark advance maps, and how the maps that we've all been passing back and forth all these years got to be so poorly shaped in the first place.

At 14.7:1 I get detonation on my stock VVT engine at 35* advance and higher (stock-ish cam advance in that area) and saw an increase in fuel economy by dropping down to ~31* advance. I get what you're saying, but also remember that some of us are getting beyond 30mpg at 75mph+ (34mpg in my case), and that's better than stock.

I'm going to do some experimenting next weekend on the dyno and see what happens.

But is your trigger latency correct?

Is that a problem on the factory NB sensor? I thought the NB sensor meant I didn't have to jack with it.

Sure, here:

https://www.miataturbo.net/attachmen...1&d=1354054649

Keep in mind this was from a long time ago. Looking at it now, I plan to do a LOT of things differently with my current 01. Also considering the engine was built, I could have ran like 30% more timing just about everywhere, but it was "good enough" and I was lazy lol

It's not a "problem", it's just an adjustment. The total end-to-end latency (from the sensor to the spark plug) will be slightly different on every configuration, and this also includes the ECU itself.

Find a new dyno if this is the case. Mustang dynos, at least the new-ish ones, have an internal map sensor with a hose to T into somewhere on the engine.

So, when you say "I ran 40° like a boss" what you actually mean is "I ran high 20s to low 30s in the midrange, just like the first crappy map that Joe posted originally."

Meaning you're retarded. (pun.)


I refuse to believe that my little shortnose 1.6 is somehow special or unique among all Miata engines in that it enjoys 10° more timing across the board than all the rest of them.

By the same token, I don't want to believe that everyone else is running around with crappy, sub-optimal spark advance maps that provide really poor cruise performance which is masked by the fact that they have access to boost when they want to accelerate.

FML

QQ

(i)

I go back to my previous statement "it felt fine/good, and got 29mpg"

On another note, and just being devils advocate here, but what if you pop open your motor in a year and find severely fubard pistons cause it was knocking but you didn't feel/hear it? just sayin

Then I will know that the motor was knocking but I didn't hear it, and I will assume that this is because I had been running too much spark advance.

18psi and I both have 10:1 engines, you have 9.0 or less.

9.4:1, but your point is well taken. NB = slightly higher static CR and probably higher VE for a given MAP / TP. So your 80 kPa is probably closer to my 90 kPa in terms of cylinder fill and chamber pressure.

Still, does this account for 10-° less advance?

I wouldn't be surprised if it did.
Obviously I'm just guessing though.

I'm keeping my eye on this thread and interested to see how your car holds up. Esp since its on 87 (if we call CA 91 "camel piss", then 87 must be "donkey diarrhea" :giggle: )

In my extensive (lol) dyno experience, yes.

It would appear that I may be approaching the point of diminishing returns, at least in this particular load zone.

Ran another set of logs tonight in the exact same spot as last night.

To start with, I ran the same spark map that was the "after" map from last night, just to re-verify it as a baseline.

The map:

https://www.miataturbo.net/attachmen...1&d=1354070352

And the log:

https://www.miataturbo.net/attachmen...1&d=1354070352

Pretty close to last night's results. A tad more fuel, but then conditions were slightly different.



The I loaded a more advanced map:

https://www.miataturbo.net/attachmen...1&d=1354070352

And logged it:

https://www.miataturbo.net/attachmen...1&d=1354070352

I didn't quite nail this one perfectly, as the RPM was slightly too high and I was also accelerating very slowly. You can see that I am very gradually letting off the throttle in this map. Comparatively, it's interesting. Very slightly more TPS and RPM, MAP is exactly the same at the point where the cursor is sitting (makes sense) and fuel PW is very slightly lower. So an improvement, but not nearly as dramatic as the last set.

The averages:

Run 1:

RPM: 3291
TPS: 17.9%
MAP: 76.7 kPa
Spark: 37.6°
Fuel PW: 7.34 ms


Run 2:

RPM: 3336
TPS: 18.2%
MAP: 76.6 kPa
Spark: 43.5°
Fuel PW: 7.29 ms

Actually, those two runs were closer than I though. All variables within 0.5% or less, average AFR was within 0.15 between the two runs as well (damn, I'm good.), and fuel decreased by an almost immeasurable amount. It's in the noise floor.

I think I have found the most optimum spark advance for 3,300 RPM at 76 kPa- I'm gonna call it ~ 38°. Only a hundred and forty-three more cells to test.

I think it's important to lay down the concept, if only for others, that the spark map should be at MBT in all cells (barring knock).

And this is actually quite a difficult concept to grasp for a lot of "tuners".

Lots of load holding dynos have a hose that you plug into your IM in order for it to log MAP. They also log the engine RPM, and wheel torque. It's a matter of a quick and easy software routine to plot torque vs. MAP, or torque/MAP vs. MAP. To me its fucking obvious, and I'm surprised the tuning dyno cos haven't written it. I guess, and mt.net is a testament to it, "tuners" aren't interested in part-throttle optimization.

Have you actually tried it? It's hard to hit and hold a fixed part-throttle MAP value with your right foot, the engine heats up, and it's hard to get consistency, enough to find 2% changes in torque with timing changes. It is frustratingly time consuming, compared to WOT tuning, while the dyno clock is ticking at $2 per minute.

When tuning WOT spark, most people will sweep RPM and plot torque vs. RPM. Then they advance the whole MAP row by 2* and repeat, and look for which RPMs where there were gains. They do this instead of tuning one cell at a time. The reason for doing this is you do one pull, and you get to look at multiple RPMs. It saves time. If a dyno could plot torque vs. MAP at a fixed RPM, then you could more quickly tune multiple MAP points for a given RPM, because you sweep an entire RPM row, at multiple MAP points.

And, my whole point in starting that other thread, was due to frustration with tuning part-throttle spark maps, on the street. Joe seems happy to tune 1 cell at a time on the street. I'm not happy even doing it on a dyno one cell at a time. Try doing that with 16 cells.

The "official" OE way to do it (read: lots of time and automated dynos), is indeed 1 cell at a time, but you generate a "spark hook" (IIRC), per cell. The "spark hook" curve is the most accurate (but time consuming) way of finding MBT. You plot torque vs. advance for a given cell (one combo of RPM and MAP), and you look at the resulting bell shaped "hook" curve. You can very accurately interpolate the highest torque point.

I've done it that way, and the car has a cvt which complicated things quite a bit. I basically had to do it backwards and side ways since the dyno could hold a certain wheel speed which would give me a range of RPM and load that I could work in with tps before moving to the next wheel speed. It feels really weird to be a 95kpa at 11k rpm and hitting a plateau at 48* of timing pushing past 50* to see if there's any more power up there then backing it back down... and being excited you improved from 20 ft-lb to 24 ft-lb.

But I havent had that kind of time on a dyno outside of those cars, since I havent had something really worthy of that level of dyno tune.