[Diy_efi] Importance of TPS with lightweight cars

[Adam Wade]

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

>>> Seems like the more responsiveness the engine/
>>> vehicle combination has (lightweight, easy-revving
>>> motor combined with light chassis), the LESS it
>>> needs acceleration mapping, because it can
>>> accelerate enough to keep intake air velocity up.

> Adam: Is some of this related to the fact that
> goosing the throttle on a sports bike is a very bad
> thing to do and the power/weight is such that you
> need to feed the throttle in far more carefully?

Well, while in most riding conditions you are correct,
often you WANT to whack the throttle open for drag
racing or wheelies, and motorcycles don't bog when you
do that (if tuned properly).  So while fine throttle
control is necessary to not wreck on bikes, especially
light/powerful ones, I don't believe that we're
looking at anything to do with being sensitive to
full-throttle application.

In fact, when dyno testing, I would often test
responsiveness on carbed bikes especially by whacking
the throttle wide open under load.  Now, CV carbs have
a self-controlling slide, not opening any more quickly
than the bike can accept the increase in venturi size,
but they still open really quickly compared to most
vehicles.

A good comparison for the finesse necessary would be
to think of driving a 427 Cobra around a corner.  You
don't stay off heavy throttle application to prevent
the engine bogging, you stay off it because you'll
spin the car if you try.

> Given how much more sensitive to bog a low inertia
> engine is there must be some sort of TPSdot
> fitted.

I disagree.  I think low-inertia small engines are
LESS sensitive to bog, because they can spool up much
more quickly, and don't let the IA velocity drop as
much.  As I mentioned, the bigger the pistons, the
more of an issue this becomes, and the only bikes *I*
have seen that use PE maps on their stock systems are
1000cc v-twins.

IT would be very interesting to track IA velocity in a
number of different bikes and cars, checking design
criteria (engine speed, TB diameter, intake
runner/port diameter, cylinder displacement, and
reciprocating mass of the engine).  I came to my
conclusion based on a combination of experience and
theory, and I'd be interested to see if I could make
them overlap thoroughly enough to be able to make a
pronouncement on the subject that was largely
irrefutable.  I was sort of hoping more people would
weigh in, and add to the data pool.

=====
| 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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