[Diy_efi] Importance of TPS with lightweight cars

[Adam Wade]

--- William Shurvinton <shurvinton at orange.net> wrote:

> I'm well ware of the need for alpha-n operation on
> bikes at low speeds having helped put one of the
> MegaSquirts on a fireblade.

Didn't mean to doubt your knowledge.  I was just using
motorcycles as an example of a low-mass motor drivign
a low-mass vehicle.

Incidentally, I'd really like to discuss your
experiences with the MS and the 'blade off-list, as I
am writing a series of books on motorcycle fuel
injection.

> However I'm less concerned with air velocity issues
> and more concerned with the best tuning approach.

I believe they go hand-in-hand.  If the air velocity
doesn't drop, there's no need for an enirchening setup
for acceleration; you'll get as good atomization as
with steady-state running, and will require an almost
identical mixture.  As I'm sure you know, this is a
big advantage to CV carbs, and why Yamaha (funnily
enough) made their throttle bodies on the R1 as
vacuum-slide bodies, like a CV carb with no fuel.

If a vehicle's drivetrain is responsive enough, and
mass is low enough, then the intake velocity won't
drop much upon throttle opening, and an acceleration
enrichment map won't be necessary.  If the engine is
sluggish, or the vehicle heavy in comparison to the
power output, then the throttle can be opened quickly
with a huge drop in IA velocity, necessitating
enrichment.  So it would mostly seem to depend on the
COMBINATION of engine design/mass, and vehicle
power/mass ratio, although I have not looked deeply
enough into it to give a useful formula for making
that decision.

> Still answers the question why bikes have MAP
> sensors connected to the runners, which I had
> wondered about.

Especially on big twins, it is difficult to get a
useful reading of IAP from the airbox.  It jumps aqll
over the place.  Only at very high rpms does it start
to "smooth out".  Which of course is the whole reason
most vehicles have both a TPS and a MAP/MAF setup... 
Not only for acceleration fueling off delta TPS, but
because MAP/MAF is much more useful at higher engine
speeds, but is more erratic at lower ones.

=====
| 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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