[Diy_efi] Importance of TPS with lightweight cars

[Adam Wade]

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

> Makes me wonder if the tuning strategy shouldn't be
> to lean off as far as possible through most of the
> range and then have a fairly agressive acceleration
> and PE strategy  to handle when you open out the
> throttle.  Seems to be sensible, but most of the
> stuff I have read on tuning light cars has been
> track oriented, where you focus on peak power and
> are less worried about the drivability and economy
> side of it.

Not with cars, but plenty with motorcycles.

Most bikes don't have acceleration tables AFAIK.  They
run TPS almost exclusively at small throttle openings,
and MAP/IAT at wider throttle openings and higher
rpms, in most cases.  Since the vehicles are light and
the engines have low inertia, there is very little
drop in airspeed when one whacks the throttle open
(except at very low RPMs), and as long as the
injection is efficient at lower airspeeds (i.e.,
injector is as close to the intake valve as possible),
there is no problem.

The only bikes I can recall having seen with an
acceleration map built in to the ECU right off are big
v-twin engines, where the throttle bodies are much
larger and you can drop the intake air velocity much
more by both a larger minimum restriction at WOT and a
heavier, slower-turning engine that takes longer to
accelerate, especially at low rpms.

You'll also notice that nearly no motorcycle
carburetors have accelerator pumps, and aside from the
widespread use of CV carbs in recent bikes, there has
been extensive historical and racing use of
cable-operated slide carbs that have nothing but
intake air velocity to draw fuel, and they have gotten
along all right.

Seems like the more responsiveness the engine/vehicle
combination has (lightweight, easy-revving motor
combines with light chassis), the LESS it needs
acceleration mapping, because it can accelerate enough
to keep intake air velocity up.  Like with starting
issues, the big problem seems to be when intake
velocity drops.

=====
| 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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