Ian C Posted January 3, 2002 Share Posted January 3, 2002 In my further quest for knowledge, I come to the subject of Air/Fuel Controllers. I don't know where the Air Flow Meter is located on the MkIV, but if it's post-turbo, and thus measures the airflow rate after it's been boosted, why would you need an A/FC? The ECU gets the airflow information and adjusts it's fuelling map to compensate, surely? A/FCs seem to function by intercepting the AFM voltage signal and 'frigging' it in a number of configurable ways. The A/FC I have, the Apexi unit, seems (on initial investigation) to add a generic percentage of adjustment, and then a further % adjustment curve defined by eight points across the rev range. This can be set up for a 'low' throttle opening, and a 'hi' throttle opening. Why would you need a generic % adjustment across the whole rev range, though? Surely bigger/better turbos only need extra fuelling a +ve boost pressures? And that brings me back to the AFM business, surely the ECU knows the incoming air flow anyway and will fuel it properly? And would the initial setup of these things generally just enrich the flow as revs increase in the 'Hi' throttle mode? And also, doesn't the fuelling requirements hinge around boost pressure/air flow rather than just rpm? Confused. -Ian Quote Link to comment Share on other sites More sharing options...
Alex Posted January 4, 2002 Share Posted January 4, 2002 As I understand it....and I maybe very wrong 1 thing that you may or may not be aware of is that the fuel map the stock ECU has is for up to 1 bar of boost. As you increase air at higher boost the ECU simply doesn't know what to do about it. thus you run lean. But, running Hybrids means that the amount of air at 1 bar of pressure is larger than the amount of air from stock T's therefore without a fuel computer to re-calibrate for the extra air (the Hybrids give you) you would run lean throughout the WOT rev range. I realise I'm being ultra simplistic but I hope that helps...have you tried talking to Leon about your fueling issue? He should be fully aware of who to set up a fuel computer when Hybrids are inplace. Can anyone confirm or deny my understanding of the fueling issue...would I be right in assuming that if you know the % of volume increase you can gestimate the % of increased fueling required? Quote Link to comment Share on other sites More sharing options...
Ian C Posted January 4, 2002 Author Share Posted January 4, 2002 I've made a blooper already - there isn't a generic adjustment %age, I don't know *where* I got that from I've also learned that the AFC takes the eight rpm range settings for both the hi and lo throttle settings, and interpolates between them, not only across the whole rev range but also across the whole throttle position range! So, e.g., if you are at 55% throttle at 4500rpm but have only got settings for 4000 and 5000 rpm at 15% and 85% throttle, it will compute an intelligent 'average' with the revs and throttle position. Does that make sense? All this means that setting them up must be a right bugger, and I've long discounted trying to guesstimate, especially with one detonated engine behind me (literally when working on the car in the garage - laugh). Regarding the volume of air increase with hybrids issue, again wouldn't the stock AFM catch any of that and fuel adequately for it, up to 1bar of pressure? And if the AFC is then only needed over 1bar, why the cluck doesn't it use a wider ranging AFM instead of ferkling around with revs and throttle position? Is this, ultimately, the reason why they are considered a 'cludge' style add on? Because they can't really *react* to the airflow and fuelling requirements of the modified engine but instead follow a strict setup map that needs to be revisited and revised with each modification? And they would always have to be worst-case scenario, e.g. set up for the highest boost you will run, and therefore probably overfuelling if you don't run full boost (thus negating the need for the two boost settings on the Apexi AVC-R?!?!) I can understand the arguments for a remappable ECU in light of these investigations... This sort of addon will probably always overfuel to be safe. Arguments on a post card to - Ian's got it all wrong, c/o the MkIVSupraNet bbs :biggrin: -Ian Quote Link to comment Share on other sites More sharing options...
Alex Posted January 4, 2002 Share Posted January 4, 2002 Quote: from Ian C on 12:24 am on Jan. 4, 2002[br] Regarding the volume of air increase with hybrids issue, again wouldn't the stock AFM catch any of that and fuel adequately for it, up to 1bar of pressure? And if the AFC is then only needed over 1bar, why the cluck doesn't it use a wider ranging AFM instead of ferkling around with revs and throttle position? I see your point but I believe you think the ECU is more intelligent and unconstrained than it really is. Otherwise why would someone pay £1400 for a Mines ECU which had a new map for up to *only* 1.1bar. Quote Link to comment Share on other sites More sharing options...
Rich J Posted January 4, 2002 Share Posted January 4, 2002 Regarding the volume of air increase with hybrids issue, again wouldn't the stock AFM catch any of that and fuel adequately for it, up to 1bar of pressure? And if the AFC is then only needed over 1bar, why the cluck doesn't it use a wider ranging AFM instead of ferkling around with revs and throttle position? The Jap spec Supra does not have an AFM it only has a MAP sensor, so you can't "measure" the amount of air coming in you can only use manifold pressure, revs, and throttle pos. etc. and calculate how much air is coming in from that, with the hybrids in the ECU will not not calc the amount of air properly as the air "pumped" at 1bar will be more by volume with the hybrid turbos than with std turbos. Quote Link to comment Share on other sites More sharing options...
Ian C Posted January 4, 2002 Author Share Posted January 4, 2002 Aha, well, that's a start on the path of learning! Righto, the MAP sensor is, I assume after the turbos in the induction path, i.e. in the actual intake manifold. What I don't understand, though, is the pressure/volume thing. Surely if you measure 1 bar of pressure in the manifold, it's got to be x volume of air, no matter what turbos are pushing it in? If you shove in more air, the volume will be the same as it physically can't take up more space in the induction system, so the pressure (and therefore density) goes up instead. So the intake pressure would be directly related to the amount of air going in, and nowt to do with volume as that's a constant. This is not gospel, please educate me I recall others saying the boost pressure isn't the be all and end all, but I can't figure out why not :biggrin: Alex - someone would spend cash on a MINES ECU for exactly the reasons I covered - it would read in the info from the engine sensors and control the fuelling for a modified engine (once set up) across the board like the stock ECU does for a stock engine, and unlike the AFC which fudges the stock ECU with averages based on relatively few mapping points and not a lot of feedback from the engine sensors. A bit like comparing GPS to roadsigns... But I could be utterly wrong, I mean, for all I know the stock ECU just has a few mapping points and extrapolates interim values from them, like the AFC does! I'm not saying any of this horse puckey I'm spouting is correct, I'm just trying to learn what's what, and discussion like this is the best way -Ian Quote Link to comment Share on other sites More sharing options...
GavinL Posted January 4, 2002 Share Posted January 4, 2002 Quote: from Ian C on 11:18 am on Jan. 4, 2002[br]Aha, well, that's a start on the path of learning! Righto, the MAP sensor is, I assume after the turbos in the induction path, i.e. in the actual intake manifold. What I don't understand, though, is the pressure/volume thing. Surely if you measure 1 bar of pressure in the manifold, it's got to be x volume of air, no matter what turbos are pushing it in? If you shove in more air, the volume will be the same as it physically can't take up more space in the induction system, so the pressure (and therefore density) goes up instead. So the intake pressure would be directly related to the amount of air going in, and nowt to do with volume as that's a constant. -Ian I'm no expert but would flow rates be a factor in this discusssion. I agree that 1 bar in the manifold is 1 bar in the manifold regardless of what turbo is doing the work. But a hybrid turbo or above should by it's nature be capable of not only greater boost levels but greater air flow rates as well. on the other hand I may well be talking rubbish Quote Link to comment Share on other sites More sharing options...
Bradb Posted January 4, 2002 Share Posted January 4, 2002 What's a manifold? I really wish I could understand this thread. Quote Link to comment Share on other sites More sharing options...
Ian C Posted January 4, 2002 Author Share Posted January 4, 2002 It's an origami model. -Ian Quote Link to comment Share on other sites More sharing options...
Ian C Posted January 4, 2002 Author Share Posted January 4, 2002 Quote: from GavinL on 12:19 pm on Jan. 4, 2002[br] I'm no expert but would flow rates be a factor in this discusssion. I agree that 1 bar in the manifold is 1 bar in the manifold regardless of what turbo is doing the work. But a hybrid turbo or above should by it's nature be capable of not only greater boost levels but greater air flow rates as well. on the other hand I may well be talking rubbish Oi - I'm the one talking rubbish here You mention the flow rate of a hybrid turbo. I think that's again just so that they can get to higher boost pressures while remaining within their efficiency island. I recall a technical discussion that I read a while back about MR2 turbo's. They use a CT-26 turbo, the same as the MkIII Supra, but they boost to 21psi with it. Now, this seemed odd to me as on the MkIII you couldn't go past 14psi without leaving it's efficiency map. What the technical thread proceeded to explain, though, is that flow rates affect turbo efficiency. As the MR2 has 2.0l capacity and the Supra has 3.0l capacity, the same air *flow* rate from a ct-26 will give 50% more pressure in the MR2 as the Supra has 50% more space to fit it into. Hence, 14psi max boost on the Supra, 21psi max boost on the MR2, but still the same amount of air delivered... So from this I figure that the more air you flow, the higher the (boost) pressure you are running - the hybrids just allow a higher boost pressure, and it leads me to these questions for us to mull over: *What psi can hybrids run up to over and above stock turbos due to their improved flow characteristics? *Would the stock ECU function perfectly OK with 1bar or less pressures, regardless of the turbos used to generate this pressure? *Would the HKS GT Twin kit running at 1bar, or a big f-off single running at 1bar, give the same airflow as stock twins running at 1bar? -Ian Quote Link to comment Share on other sites More sharing options...
Syed Shah Posted January 4, 2002 Share Posted January 4, 2002 Nope, a bigger turbo will flow more air at a given boost pressure, which is why a big turbo can give you more power even at lower boost levels Quote Link to comment Share on other sites More sharing options...
Ian C Posted January 5, 2002 Author Share Posted January 5, 2002 A bigger turbo may be capable of flowing more air due to it's bigger inlet, exit, and compressor wheels, but it's all still going into the same volume - intercooler, manifold, cylinders, and associated piping. Therefore, how can more air enter that same volume without the pressure going up? Am I missing something fundamental here? Also, at what point do we measure the boost pressure? I thought it was in the manifold? Quote Link to comment Share on other sites More sharing options...
GavinL Posted January 5, 2002 Share Posted January 5, 2002 Quote: from Ian C on 12:58 am on Jan. 5, 2002[br]A bigger turbo may be capable of flowing more air due to it's bigger inlet, exit, and compressor wheels, but it's all still going into the same volume - intercooler, manifold, cylinders, and associated piping. Therefore, how can more air enter that same volume without the pressure going up? Am I missing something fundamental here? quote] How about it just goes in and out quicker. i.e you can pump more water through a 4" pipe at 1 bar than a 2" pipe at 1 bar. Uprated turbos often come with larger manifolds along with larger intercoolers, bigger exhausts etc to ensure good flow I think the pressure increase will be manifest itself in the cylinders as this is ultimately more air and fuel = more power. In practice this must be the case. I have hybrid turbo's on my car and there is more power at stock boost than with the standard turbo's. Quote Link to comment Share on other sites More sharing options...
Ian C Posted January 5, 2002 Author Share Posted January 5, 2002 Righto. If you have experimental proof, cool. Theory aside (phew, says everyone) then, the AFC is needed with hybrids, and especially hybrids that run above 1bar boost, yes? So mostly the AFC would trick the ECU into adding fuel at fairly wide throttle openings, yes? Why would it ever need to lean the mixture out? -Ian Quote Link to comment Share on other sites More sharing options...
Rich J Posted January 5, 2002 Share Posted January 5, 2002 Quote: from Ian C on 2:10 pm on Jan. 5, 2002[br]Righto. If you have experimental proof, cool. Theory aside (phew, says everyone) then, the AFC is needed with hybrids, and especially hybrids that run above 1bar boost, yes? So mostly the AFC would trick the ECU into adding fuel at fairly wide throttle openings, yes? Why would it ever need to lean the mixture out? -Ian You will need bigger injectors or increased fuel pressure first as the AFC adjusts the MAP sensor pressure signal so if you increase the pressure signal (to get more fuel) you will just hit fuel cut earlier, so you have to start from a rich condition (with the bigger injectors or raised fuel pressure) and then use the AFC to lean out the rich spots. Probably best to get the WOT just right/slightly rich and then use the AFC to lean out/enrichen any spots and the non-WOT fueling Quote Link to comment Share on other sites More sharing options...
Ian C Posted January 6, 2002 Author Share Posted January 6, 2002 Sounds reasonable. Basically it's factoring up the fuel by the same amount as the increased air supply, so the ECU thinks both are still stock, and then fine-tuning the range to avoid over or under fuelled spots. I had an epiphany whilst talking to Alex, regarding how a bigger/better turbo can flow more air at the same pressure. The third side of the equation is temperature, and a more efficient turbo / one with bigger ports will not heat the air as much as it compresses! Therefore, cooler air at the same pressure = more oxygen = more power. Sound reasonable? Blimey - I'm happier now as I know some more - thanks all that participated in this :biggrin: -Ian Quote Link to comment Share on other sites More sharing options...
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