Dan Bailey

MEGA late responding to this, I had an insane year last year but this stuff still hasn't left my mind. Agreed, the MAP/EMAP pressure ratio option would be quite nice too and I have in my head added that as a wishlist item at some point in the past and wasn't well received - though I've asked for a few weird things ;) A couple of things which come to mind as an advantage for IMAP/EMAP aside from what you already listed, is if people are playing with things which manipulate the exhaust flow to improve spool etc. Variable geometry turbos, quick spool valves, compressed gas injection into the turbine etc which would result in the engine's VE changing for a given RPM/MGP cell.

Know that situation too well. All good, cheers!

Cheers Adam, yeah I am pretty familiar with how the Link does it's base fuel calculations - or at least with how the documentation states it does it, and have been tuning them for a few years now so thus far I think I am reasonably familiar with it though absolutely accept that I don't know EXACTLY how it works so understand I could be incorrect. All the documentation and logging seem to indicate that the MGP value recommended to be used in the fuel table look up is "MAP - BAP" and that is what I am suggesting isn't ideal. Just to be clear here, I'm talking about looking up a value from the fuel table - NOT the fuel calculation done after the fact. I understand the Fuel=MAP part of the fuel equation later down the line deals with baro etc correction, but if the VE or PW value looked up from the main fuel table in the first place is incorrect then it's just doing good calculations on the wrong data. Also, I realise that in most cases people probably won't have any real issue - however to show where and how there could/probably would be issue if you are being pedantic I threw together a graph showing how far off the "MGP" look up would be from what it SHOULD be looking up if you had a properly corrected load look up. This example assumes a car was tuned on a "typical" day at sealevel, say 1013ish hPa - the X-axis is to show different ambient pressures, each line represents manifold absolute pressure and on the Y-axis you can see the error (+/- x kPa) that the fuel table look up would be for that given MAP and BAP combination. It shows that in any situation the baro pressure is exactly that every load point will be on point, however the more baro correction involved, the greater the error. Unfortunately I don't have the ability to take a car with a Link in it for a drive to Taupo and back to Wellington to get logging to prove the theory, a bit of a shame as timed right this low coming through could really offer some pretty sweet barometric pressures if you were at a decent altitude I've also attached a screenshot of some code from one of the freely available MoTEC M1 Packages showing they do the same thing as what I am suggesting/requesting. Obviously, if this change happens this can't be a "fix" as any fuel map done using gauge pressure would need the fuel table to be remapped - it would be a different kind of load option. Hope this explains what I'm getting at and why, let me know if there is anything clearly wrong with what I'm saying - especially if the Link actually does something to deal with this. Cheers

Hi there, It has been pointed out to me, and after doing some thinking and mathsing - seems evident that using MGP as the fuel table look up axis is not an entirely accurate way of doing that look up for a VE/PW value, albeit usually being "close enough" in most cases. This is because you are just using a fixed offset from the ambient air pressure, when infact if you are operating in a different ambient pressure situation - the whole density has changed, meaning that the table you use as a part of how to effectively estimate air mass needs to be treated as running on a different scale... not just by using an offset. Funnily enough, as MAP pressure gets closer to BAP the current fuel calculation gets more "accurate" - but particularly as MAP gets lower when BAP is different to the environment the car was tuned to, the error from what it "should be" looking up gets bigger and bigger... to the point where in full vacuum you could be doing look ups to quite incorrect load zones for the environment. The logical load axis should be MAP/BAP as opposed to the current MAP-BAP - which presumably would flatten the table a little more, as well as make mixtures more consistent in different barometric conditions. I of course accept that I could just have my wires crossed, but I'm just trying to communicate as clearly as possible what has recently come up and couple explain a few things. Obviously any error is not enormous, we've been using this for YEARS with decent results - but you know, ignorance is bliss and now knowing that perhaps it could or should be better is pretty hard to ignore. Any input, corrections, questions, or changes if it makes sense would be massively appreciated Thanks, Dan [edit - I could SWEAR I put this in the Wishlist forum, though it seems to have shown up in G4+... not sure how I did that wrong, but I can't delete or change it. Sorry!!]

For sure, though that is quite similar to existing MAF based tuning solutions many people already used. Check out "engine load normalised" here: http://www.gtrlife.com/forums/topic/94501-motec-m1-tuning-questions/#entry1322267

Absolutely, I understand that - so it'd be fully usable and do the basic thing I was looking for with minimal change, it's just that the calculation I showed gives a more intuitive and "consistent" number to work with. For example, the load axis would end up looking a LITTLE like a KPA load axis with (MAP x VE) with scaling for temp correction... well the way I pictured doing it. So to just pull numbers out of the air... if your MAP was 202kpa, your VE was 110% and your IAT trim was +2% - perhaps you'd end up with 202 x 1.10 x 1.02 = 227 MagicLithUnits and it'd be a familiar looking scale... and one which would arguably be more portable, if you know what I mean? On the other hand g/cyl is locked to that engine's displacement etc.

Hi Scott, thanks for the response - I was just getting back to this... Yeah, I found that "measured" existed, but not "estimated". Actually, if it were an option (I just pulled estimated airflow/cylinder out because it was an existing parameter which was arguably a better load measure than just MAP) would be: (MAP x VE) / IAT I think there are different "nicknames" for that by other brands, but it basically adds up as meaning that the ignition table look up is done off cylinder filling at that moment but is still semi-intuitive to work with as it is normalised - the airflow numbers would be relatively arbitrary by comparison. Apologies for not making the first post a bit clearer in regards to what was hoping to achieve. Cheers, Dan

Hi Scott, Calculated Airflow: Perhaps being pedantic, but having the option of doing a timing look up based on closer to the actual mass of air going into the engine - I guess mimicking a MAF setup. There are 4d overlays which I do when tuning to deal with things which could effect VE from the base VE map "describes". At this stage for the most part it's possible to just mimic the same adjustments by doing overlays of the ignition table as well, but if there was a way of having the ignition table look up done based off what the air mass / cyl calculation (so basically incorporating VE + 4d/5d table correction, MAP and IAT) to get look up into a singular timing table. I figured it shouldn't be a huge wish list item as it is already a thing which appears to be calculated and can be logged. MAP / IMAP: Is already an option with other ECU options on the market, VE table lookup is done based off a ratio of MAP / EMAP but the fuel calc done the same as it is currently. I'll elaborate more when I have a bit more time, but it is another thing which seems to/sounds like it results in being able to dial in a nice tune easier - flattens out the fuel table and also becomes easier to update a map after mechanical changes

Hi guys, A couple of things which would be quite nice additions to "load" axis in fuel and ignition tables would be as the title suggests, calculated airflow - if not effective cylinder filling or something of that kind as an option for the ignition table axis... so for sake of argument, if you were using the modelled fuel equation mode then you could have MAP x VE as a load axis. Another one which would be nice would be MAP / EMAP as an axis option for tables & logging. I'm sure there were others which have occurred to me, but those are ones I'd definitely quite like if they were options Thanks. Dan