Barometric timing correction?

[Philip Lochner]

I think I've requested this before but respectfully want to again request this feature. I know very little about programming but I recon this feature should take the likes of James etc, 3 minutes flat to implement this feature.

Just like fuel is vitally corrected for barometric changes, please could we (us living in hilly areas) have exactly the same but for timing?

An engine tuned at sea level can have its timing advanced when travelling to higher altitudes for optimized performance at altitude. Likewise a (high compression) engine tuned at higher altitudes MUST have its timing retarded when going to lower altitudes, to prevent excessive pinging ( as I'm having ).

I live and tune at 85kpa and find that I have to retard timing by about 4 degrees when traveling to the coast (100kpa). The opposite would apply for an engine tuned at the coast. (Default curve)

[gslender]

Interesting.

I assume you mean some kind of pre-start compensation curve whereby it adds/subtracts ign etc.

Generally, why doesn't the combination of map based ign tables work? Has the air become significantly warmer/colder too? In which case, do you use the mat tables to correct for that (but just lack ign) ??

G

[Philip Lochner]

Hi G

No, I mean REAL TIME barometric timing correction.

I build ALL my MS's with real time barometric sensors having found how important it is to correct fuelling for barometric changes.

But I have found that it is just as important to correct timing for barometric changes. I live at 1500m above sea level and tune my cars at this altitude. By the time I get to 1000m above sea level my cars are pinging as if designed to do so!! This then requires manual correction of the base timing (I normally change the timing offset) but in principle this should not be necessary if this requested feature could be made available.

Map based ignition tables don't compensate for barometric changes because of dynamic differences that exist between different barometric pressures. 70kpa engine load at 85kpa barometric pressure will tolerate eg 20 deg advance but 70kpa engine load at 100kpa barometric pressure will only tolerate eg 17 deg advance. I THINK the reason for this that at 100kpa the air rushing into the engine (creating 70kpa MAP) has much greater momentum due to the greater pressure difference over the throttle and this greater momentum results in better cylinder filling meaning more fuel is required (which is why barometric fuelling correction is needed) and less advance is required (which is why I'm asking for this feature. This is also (to me anyway) the main advantage of using a MAF for load determination rather than MAP based (even though I dont use MAFs)

This problem manifests more prominently with higher compression engines where knocking is a very real problem when running on inferior fuels (too low octane). Low compression engines has a much lesser tendency to knock depending on compression ration and octane.

[Philip Lochner]

Sorry, I wanted to add:

I do use MAT based timing correction as MAT also plays a major role wrt knocking but the MAT correction table does nothing wrt barometric changes.

But yes, I hope that the code for the MAT correction can be "copied and pasted" with just a change of one variable (MAT vs Baro) and the addition of this "AdvBaroCor" factor in the timing equation. If I knew just a bit more about programming, I would attempt to do so myself. Frustrating...

[gslender]

I build ALL my MS's with real time barometric sensors having found how important it is to correct fuelling for barometric changes.

Never knew it supported them. I've added mods and sniff over most of the ms2 code and admit I've never seen mention of them either. Not sure even how to begin to help...

G

[muythaibxr]

It shouldn't be too hard to do an offset.

Ken

[dontz125]

<cheeky code-clueless heckler mode/> You're doing major coding mods, and you DON'T KNOW ALL THE POSSIBLE OPERATING MODES?! For shame! </hc-chm>

Seriously, a lot of people do use the real-time baro correction. With full-power 20-20 hindsight, it does seem pretty obvious, and I'm surprised that it's taken this long for it to be recognised as an issue. I would wager that a 2x2 chart (adder deg vs Baro kPa; 0 @ 85, -3 @ 100, to use Philip's example above) would solve most of the problem. I'd be surprised if a 6x6 chart was needed.


Philip: You're somewhat correct in your analysis regarding momentum, in that there are more molecules sitting in the intake manifold available to be drawn in.

[Philip Lochner]

I would wager that a 2x2 chart (adder deg vs Baro kPa; 0 @ 85, -3 @ 100, to use Philip's example above) would solve most of the problem. I'd be surprised if a 6x6 chart was needed.

Well spotted! Yes, I would like to suggest a 3x3 chart (for dudes like me who tune at altitude). Very little in the internal combustion engine is ever linear. This would enable timing retardation when going to lower altitudes and advance when going to higher altitudes. Guys who tune at sea level (I hope they realise how fortunate the are in a MS sense ...) will only need to adjust in one direction, advancing for higher altitudes.

PS: It would not surprise me if optimal timing adjustment is not just a function of baro but also RPM and MAP - but let's not go there...

[pigga]

Hi Philip - just out of curiosity: What's the Octane number of the fuel available at your location?
Thomas

[gslender]

Ok, I've read up now on the 2nd Map sensor option and see in the code where it's used as the baro correction for fuel.

It would be fairly trivial to add a spark correction table ... a 3 x 3 table would be a simple to do.

As I'm currently away from home and bound to an iPad, and unable to launch TS, can you outline for me which sensor input the 2nd baro map sensor uses... As the MS2 is fairly limited in the number of inputs, just curious what it consumes to get that 2nd sensor reading in....

G

[gslender]

As I'm currently away from home and bound to an iPad, and unable to launch TS, can you outline for me which sensor input the 2nd baro map sensor uses... As the MS2 is fairly limited in the number of inputs, just curious what it consumes to get that 2nd sensor reading in....

I see in the docs it is recommended to solder sensor input to JS5 on the CPU board... So that's AD6 I think. Does TS let you choose the input or is it always JS5 ?

G

[hassmaschine]

doesn't % baro already do this for you? is your timing map 100% flat or something?

[dontz125]

gslender - you can use JS4 or JS5; using Jean's IOx board it can come in on one of eight (0-7) 'remote' ADCs.

[Philip Lochner]

Hi Philip - just out of curiosity: What's the Octane number of the fuel available at your location?
Thomas

We have 93 and 95 (unreliable supply) available where I stay - if one were to believe those numbers, that is. There is no point in tuning for 95 as every now and then 95 is unavailable and the car is un-driveable on 93 if tuned on 95.

[Philip Lochner]

doesn't % baro already do this for you? is your timing map 100% flat or something?

I dont use % baro and I dont want to use it either. I can not see how % Baro would solve my problem because at 85kpa MAP at 85KPa Baro (100% load with %baro) I can have eg 24 deg advance but at 85kpa MAP at 100kpa baro (85% load with % baro) the engine will only allow eg 20 deg Adv due to whatever dynamic effect is at play here.

My timing table is not flat at all but shaped in a typical way as for normally aspirated engines. Not sure why you would ask that?

[Token]

I will be finishing up an Alpha-N ITB'd 4age pretty soon here and the MAP is already setup for baro correction, this timing feature would be a great plus- its a high compression 4age build and the owner loves canyon runs.

[TheSilverBuick]

I would use this feature as well. Normal atmospheric pressure here is ~85kPa, and I do fairly often drive to sea level. I have the intake temp ignition retard setup, which helps when rolling through Las Vegas in summer and it's 110+*F out, but I do run into the same problems mentioned above and have to manually pull timing out of the table from what I've had setup from driving around where I live from the simple air density increase.

[gslender]

So this new function/feature of a 3x3 table that does an adder to spark, do you envisage the baro correction being realtime, or only before cranking/startup?

If I was to give this a crack, who'd be the test bunny?

G

[Red_Baron]

Barometric correction *IS* real time so it would have to be a live table that is always being looked at

RB

[TheSilverBuick]

I have a MAPDaddy real time baro installed. I won't be driving off the hill in my car for a couple months (could be March, April or May...) to really test it. I am looking at installing your firmware with the Idle targeting modifications. Mine works decently, but the reports on yours sound pretty good.