[Diy_efi] Speed-density vs. MAF/MAP...

[Adam Wade]

--- Perry Harrington <pedward at apsoft.com> wrote:

> If you take the MAP reading in sync with the tach
> signal every time you read it, the signal is
> consistent with that point in time.

And on an inline-four, where you get an intake event
every 180 degrees of crank rotation...  *light dawns*

At lower rpms, the sample rate isn't even very high.

*why do you 'need' to switch from speed-density to
alpha-n when VE goes over 100%?*

> Speed density is based on the air pressure in the
> intake being the same as the pressure on the back of
> the intake valve.  Once you hit atmospheric, which
> usually happens at 100%VE, you have run out of that
> component.  Thus it merely becomes a table where you
> are reading RPM and looking up a fueling amount for
> that RPM.

Doesn't that hold true for any speed density reading? 
You have to know the VE or the intake pressure doesn't
mean a lot, yes?

> With Alpha-N, you at least have a second component
> when the MAP runs out of resolution.

I would think that would more be a function of
properly "sizing" the sensor, or is some lighbulb
still not screwed in all the way here?

> Alpha-N is basically lower than MAP in terms of data
> inferred from sensors.  MAP is lower than MAF, as
> MAF tells you actual mass, whereas MAP infers it.

Yep, that much I had pretty much gotten, but I was
under the impression that some ranges of operation
were more "reasonable" for one system or another.

> I believe that above 100Kpa they are inferring mass
> airflow from those throttle angles.  It only makes
> sense.

Let's compare a situation where the engine is making
the same amount of power, and thus the vehicle is
running at the same speed...  In once case, at a
higher rpm but with a smaller throttle opening; in the
other, a lower rpm at a greater throttle opening.

The VE of the engine with the smaller throttle opening
is likely going to be lower (even taking into account
cam setup), yes?  So to be making the same power with
a higher VE, there's a higher air velocity, and thus a
lower pressure, yes?

Since the VE of the engine changes based on throttle
position, where's the compensation for differences in
actual air mass ingested vs. MAP (assuming you are
reading the MAP from the airbox, as a goodly number of
the vehicles I am thinking of actually use)?

> That depends on the manuf.  All the Honda EFI stuff
> I've seen has a vacuum tree tied to each TB below
> the plate.

I unfortunately haven't had a lot of chance to look at
Honda stuff yet.  I've spent most of my time with
Kawasaki and Suzuki, which do not.  I'm interested to
see how all the different manufacturers do it.

*accel enrichment*

> No, it's simpler than you think.  It goes to the old
> tuning adage of "give it what it wants".  I have
just
> recently started messing with accel enrichment on my
> 5.0 motor with the stock computer.  It's MAF and was
> most definitely suffering from lean enrichment, so I
> fattened it up.  Right now I'm running about 3x the
> enrichment at low throttle angles that the stock
> setup was running.  I also have a TB that is 67%
> larger than stock, a MAF sensor that is 72% larger,
> and the motor makes ~44% more HP and ~25% more
> torque, all within 4CID displacement.

That's pretty respectable.  I suppose my question is
then, how important is best power for anyone creating
these settings?  It's certainly possible to make it
BETTER than it was, and definitely to make it more
DRIVABLE.  I tend to think in terms of "If you're not
using something capable of achieving best power, then
why go in that direction?"  Certainly there are many
ways of making a vehicle drivable when you mash the
pedal (accelerator pumps on carbs are quite drivable),
but many of them are going to introduce fuel that is
not appropriate over the course of the acceleration
event, or not in the best manner...  Again
acceleration pumps come to mind, which clearly are not
the most efficient way of delivering fuel for an
acceleration event, and can obviously be improved
upon.

> MAF should work equally well at all points in the
> engine output.

I was more thinking of reversion issues.  They can be
minimized with a large enough airbox, of course...  I
wonder if airboxes that are designed to current
thinking would be big enough to make MAF practical at
low engine speeds on motorcycles, and maybe use the
alpha-n to run JUST an acceleration enrichment map...

> You only have to ensure it doesnt go back through
> the MAF.  If you place the MAF at the actual opening
> for the intake ducting it'd go a long way.

I now wish I had an appropriate MAF and a sportbike
sitting around to play with.  ;)

*intake exploiting large pulsations*

> Nope, I'm merely saying that you don't want your
> pulsations leaving the plenum.  If they do, you need
> to increase your intake tubing length until the MAF
> is undisturbed. 

It's inevitable that SOME energy will leave that way. 
But yes, you can reduce it to almost meaningless
levels.

> Putting large plenums before and after the MAF helps
> with this too.

Many manufacturers are fond of putting resonation
chambers right inside the intake opening to lower
intake noise levels...  I would think that in between
that resonator and the main airbox would be a good
spot.  It's also convenient physically.


=====
| Adam Wade                       1990 Kwak Zephyr 550 (Daphne) |
|   http://y42.photos.yahoo.com/bc/espresso_doppio/lst?.dir=/   |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |

__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com

_______________________________________________
Diy_efi mailing list
Diy_efi at diy-efi.org
http://www.diy-efi.org/mailman/listinfo/diy_efi