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

[Adam Wade]

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

> But where in the intake tract would you find MAP >
> atmosphere?

If you were measuring in the throttled volume, you
would find it right before you opened the intake
valve, IIANM.

> Oh, another point (non-linear thought process), if
> you have > atmospheric pressure through a MAF,
> reversion becomes a non-issue, because the intertia
> of the air prevents reversion.

I suppose that depends on what's on the other side of
the MAF, yes?  Surely you can get air to move
backwards at any intake pressure, if you have enough
pressure behind it.  I doubt you'd ever see this in a
real vehicle when intake pressure is above 1 atm.

>> As for MAF on motorbikes I have yet to see a
>> workable MAF solution that works with IR systems
>> and teeny throttled volumes without screwing up the
>> throttle response.

> I understand "if it ain't broke don't fix it".  But
> how would that be fun or challenging?

Definitely it's good to learn, although sometimes it
pays to learn from reading what's written by those who
tried it already in lieu of trying it yourself.  ;)

> Seems to me that "MAF lag" is really the inertia of
> the measured volume.

If that were the case, then MAF wouldn't need any
accel enrichment, would it?  If you were mapped to
always run at best power, adding more fuel would
create LESS acceleration...

> This goes back to Jeff Clarke's DIY-EFI discussion
> on MAP lag vs TPS.  MAP just has less lag than MAF
> due to where it's measured.

I can measure MAP in the airbox (and several bike
manufacturers do).  Doesn't MAP still have the
advantage, because when the throttle changes position
the MAP will change closer to instantaneously than a
MAF would?  Heck, wouldn't having a MAP in the
throttled volume beat having it in the airbox?

> If you made 4 tiny MAF sensors into each of the TBs,
> I'm sure you'd have a very low lag, but then you
> have a bunch of other problems.

Might make for a very interesting experiment to
demonstrate some theoretical points...

Ahh, for a research grant.  ;)

> I see the logic in MAF systems and have been working
> with one for a couple of years.

I never used to understand why they weren't on
motorcycles, but bit by bit, some reasons seems to be
coming out in my mind.

=====
| 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     |

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