Big injectors + MS hi-res question?
 

Granted hi-res gives you better resolution for larger injectors, but my question is this:

If using, say 1000cc injectors, the req fuel will be very small and I know that this is just a muliplier, but I've also read that haveing too small a req fuel can cause issues with fine tuning. So is it better to run a larger req fuel number and have lower VE numbers in the fuel table (scale the table for a higher req fuel) or just go with the lower req fuel and usual VE numbers?

low req fuel and high numbers in the VE bins will give you more resolution

low req_fuel. fiddle ve table.

throw a restrictor on the fpr line to lower the pressures :)

Ah, so then my only issue would be to re-scale if one of my VEs was above the 255 limit, which I do not expect. Thanks guys.

Right. Ideally, you want to take advantage of as much of the space as possible that's been provided for you in the VE cells- you've got from 0 - 255 to play with. I'd guess that is resolution is the concern, ideally you'd want to be well into the low 200's in the upper cells, to really maximize the range of tuning available to you.

It's ironic that this came up this morning, I just got done re-scaling my own VE table not 10 minutes ago to gain some more resolution...

n/a portion for boosted?

No. I decreased my Req. Fuel value by dividing the old value (6.1) by 1.4, giving me a new Req Fuel of 4.4. I then scaled the entire VE table by 1.4, resulting in larger numbers in each cell. IOW, I'm giving myself some more resolution to work with, causing each +/- 1 in the VE cells to be a finer increment.

Interesting. I should try a lower req fuel for the heck of it. Have the results been good so far? Are you using MLV or autotune for tuning?

The results have been that since building the new table earlier this morning, I've pretty much sat here in my pajamas drinking beer and futzing around on the forum, instead of going out to the car and loading the new MSQ. :D

MLV. I played with autotune early on, but it has a serious flaw- Autotune only tunes the one cell that you happen to be closest to at any given time, and it does not scale its correction relative to how far from the center of that cell you happen to be in. MLV is much smarter- if a certain record happens to be between four cells, slightly closer to the top ones, then MLV will portion out its corrections appropriately, weighting correction more heavily towards the upper cells.

This was the same thing that used to piss me off about the "Sampling Map" that Greddy added to the 2.1x builds of the EMU software- it recorded only one value per cell, without regard for whether you were on the edge of the cell or right in the middle. When I built the 1.6 AFM map for the EMU, I basically did the same thing (by hand) that MLV does automatically.

I've come up with a new theory- I'd like opinions.

I never got around to testing the rescaled map I did this morning, but I decided to change it again. This time, rather than pulling a number out of the air, I specifically chose 3.5 as my ReqFuel constant. Why? According to the MegaManual, the resolution of the injector PW computation with MSnS-E HR is 0.035ms. Assuming that my understanding of the PW calculation is correct, that ignoring enrichments and lag, PWactual = (VE/100)*ReqFuel, then there is now a perfect correlation in the steps between VE numbers and actual output- each VE increment of 1 should increment actual PW by exactly one step of its native resolution. This should, in theory, yield the most precise control possible.

Of course, my VE table (which I multiplied by 1.74) now has some fairly large numbers in it. Bear in mind that a lot of these cells are still untuned, but here's what it looks like presently.

http://img407.imageshack.us/img407/3418/vexv2.gif


Thoughts?

I'll take this map for a drive tomorrow and see how it goes.

Man... You are on a thought provoking streak right now. First the dyno quest thread, then the WI thermodynamics thread, and now this... Great stuff, all of it :bigtu:

It is late so I'll check your pw numbers sometime later. But, details aside, this is an excellent idea IMO.

so did you just multiply your whole table by 1.4?

basically yes

jesus christ tom. did i miss a build thread? 1000cc... what do you have up your sleeve?

Yes you missed his build thread, he bought neos old car and is getting ready to strap a rocket engine turbo to it's ass.

yeah, just got to that. this thread was more recent.

curious question/comment: does the MS extrapolate values that fall below the table values or does it make them zero? I ask because you periodically DO get below 800 rpm (cranking) and below 23 kpa (compression braking) and I'm wondering if it makes the car go haywire when you drop below those #s.

corollary: if it doesn't extrapolate, the lowest column / row should be set to a number well below you ever see. ie zero kpa / zero rpm. the hydra has this hard coded so there's always a 0 on both.

The MS has separate features that account for cranking and compression braking. Those being the cranking table where the ve table isnt active until after the car has started, and over run fuel cut where the injectors are shut down after being below a user set kpa for >1s.

Success. The new table works nicely with the 3.5 ReqFuel constant. It needs some fine-tuning (nothing that MLV has been unable to deal with) but it's definitely operational. Took it all the way to 11PSI with nary a hiccup, and I'm hoping it's not my imagination, but my idle AFRs seem a tad more stable. I wonder if my recent troubles in finding a dyno have been the work of a higher power, denying me access until this hurdle was overcome...

What a happy coincidence that the fueling requirements of the Miata engine, coupled with the 440cc injectors that I just happened to have, allowed this rather unusual ReqFuel configuration to work.

y8s, the MS does indeed seem to extrapolate off the edges of the table. My idle, which is still not 100% perfect, occasionally dips down into the 500-600 range, and even then the fueling continues properly.

Damn it Joe, I didn't want you to find out but I'm busted. Now you may go find a dyno.