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...