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VE and Throttle Position Fuel Maps

EFI Tuning Fundamentals

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New guy here. I hope y'all might be able to assist me.

I have an aRacer RC Super 2 ECU on my Yami MT-07 race bike (2 cylinder, DOHC 4 valve, NA). It primarily relies on volumetric efficiency (intake air pressure) and rpm for its base fuel and spark maps. There are also throttle position by rpm fuel and spark maps which appear to be intended, when appropriate, to modify the air pressure-based maps. As I understand how the two sets of maps interact, the TP maps can increase or decrease the numbers generated by the VE-based maps by a percentage. The base throttle position maps provided by aRacer are set at 100% (so, basically, the throttle position maps don't have an effect on the VE-based maps). As an example, if I were to input 102 into the TP fuel map at 50% TP and up, my fuel would be enrichened by 2% when 1/2 throttle to WOT.

Can anyone help me to understand when/why I might want to use the throttle position maps to "trim" (reduce or increase) the fuel or spark generated by the air pressure maps rather than making changes directly to the air pressure-based maps? My initial tune will be done on a load-bearing dyno, while any at-track adjustments might be more easily done (at least easier for me to understand) by using the TP-based maps. Have I answered my own question?

My understanding is most motorcycle aftermarket ECUs (actually, piggy-back systems) rely on TP-based maps, and I've found that most folks in the motorcycle tuning world seem uncomfortable dealing with VE-based tuning software. There is also a dearth of english-language support from aRacer (Taiwanese company), so we end users are left to figure this stuff out on our own.

No idea about this particular ECU, but I'll talk about generic information.

MT-07 have individual throttle bodies, so in general it should be the TPS as main fuel load. This method is called Alpha-N. The reason why it is used with ITBs is because the flow is very non-linear in accordance with the throttle opening. At low opening, the air flow increases rapidly compared to high opening. You can still use MAP with alpha-n, but it uses a compensation table to account for the increased pressure in certain areas. This is useful when using boost.

MAP can still be used for ignition.

Thanks for your thoughts, Frank. Yes, the MT-07, like nearly every other fuel injected motorcycle has individual throttle bodies. What you didn't quite say but likely were assuming is that measured intake pressure at moderate loads is not significantly different from what it is at high loads; which, if so, would certainly make relying on intake pressure a poor basis for determining fuel supply.

I don't have access to the formulas used by the aRacer ECU but I can tell you from reviewing data log tracings of rpm, AFR, throttle position, and "engine air pressure" that the tracings of throttle position and engine air pressure are very similar (they go up and down together and reasonably proportionately, and air pressure is at its highest at WOT and lowest at closed throttle. As would be expected with the non-linear flow, throttle changes in that upper third (66% and up TPS) are greater than the corresponding changes in air pressure. The engine air pressure data certainly doesn't reflect anywhere near the same values at 1/2 throttle or 2/3 throttle as at full throttle.

In any event, I'm stuck with intake air pressure as the primary determinant for fuel supply unless I want to change my ECU.

I think you're missing a critical factor, the throttle position.

Exactly where is this "air pressure" being measured? I would assume it's in the air box.

Have a GOOD look around the throttle bodies, if there is any sort of electrical connection there, then there will be a TPS map you need to account for. I would expect you to find at least one as darned if I can see how the mapping would work otherwise.

Thanks Gord. Air pressure is measured after the butterfly and right before the rubber boot that mounts the throttle body to the cylinder head for the #1 cylinder. There is no connection to the second throttle body and there is no air box; just a nice bell mouth and a K&N filter.

There are throttle position based fuel and spark advance tables, as I indicated in my initial post, but they are intended by the ECU manufacturer as a way to adjust the intake air pressure-based maps rather than to replace them.

As an example, imagine a base fuel map with rpm on one axis and air pressure on the other axis. Each of the cells then has a number ranging from 180 to 300 or so. The TPS x rpm fuel map from aRacer also has many cells but they all read 100. ARacer indicates that 100 means no change in the fueling (based on the air pressure map), and that 95 would mean a 5% decrease in fuel at that throttle opening and 105 would mean a 5% increase in fuel, for example.

The cells of the air x rpm spark map contain the spark advance in degrees. The TPS x rpm spark map then allows changes from the air pressure based map in the advance of x degrees at the indicated rpm and throttle position. Although aRacer intends that spark advance be determined primarily based on intake air pressure, I can at least see a straightforward way to rely exclusively on throttle position for spark advance (put 1s in all the cells of the air-based map and then the desired spark advance, less one degree, in the TPS spark table. Well, it should work, anyways. I could try to do the same thing with the fuel maps but it would be decidedly more complicated than setting spark advance based on throttle position.

I believe the stock Yamaha ECU relies primarily on intake air pressure x rpm for fueling up to around 50% throttle, and then it relies primarily or nearly exclusively on throttle position thereafter. The piggy-back fuel controllers for motorcycles, like the Dynojet products, all seem to rely on throttle position for making changes to fuel.I don't know why aRacer decided to follow its own course and, much to my chagrin, there is no one to ask, at least not in English. That's why I'm bothering you guys....

I wonder if they are generating a pseudo MAP channel based on throttle position, working like the Inlet Manifold Pressure Estimate table does in a MoTeC M1 configured to operate with ITB's?

I dunno, Stephen. All of the intended applications for the aRacer stuff use ITBs, so perhaps something is going on in the background calculations. The only guidance aRacer provides is limited to a bunch of videos and a power-point presentation.

They show how to use the software to modify the numbers in base fuel map (intake air pressure based) provided by aRacer to achieve target AFR but, other than pointing to the existence of a throttle based map to add or subtract % fuel as calculated by the air pressure map, don't say or show anything about using the throttle based maps. For what is is worth, the target AFR map is throttle-based, and so are the maps that allow fuel (by percentage of fuel from the base air pressure map) and spark (by degrees) changes by gear, but they don't actually use those tables in their materials.

Ah, I mis-understood before, and may still be doing so, I thought it may have been a pressure monitor for the ram air pressure change.

It's basically air flow/density vs rpm, which is much simpler.

It seems like the eRacer ECU has multiple options, some of which may not be used with this application - for example, it seems like there's no TPS on the bike, so that can't affect the fueling map because there will be no way to change that map

Gord, there is a throttle position sensor on the motor, and their are TPS based maps; they just aren't used for base fuel settings, but instead, according to aRacer, are intended to be used to adjust the intake air pressure map. I can make manual changes to all maps and, more specifically, I can make changes to the base air pressure map and/or the throttle position map based on WBO2 AFR readings. Most of the maps and options seem pretty typical for an aftermarket ECU; what is weird, I'm now learning, is the aRacer ECU's intention that intake air pressure be the predominate basis for determining engine load and fuel.

Thanks for your interest in helping me to understand what I have and how I'm supposed to use it. I wouldn't have to do this if I could find someone in the eastern third of the U.S. that has experience with aRacer tuning, but the very few are too busy preparing their Moto America bikes for Daytona. Instead, I have to go with someone with dyno-based tuning experience to whom I can try to explain the aRacer software.

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