[Diy_efi] Importance of TPS with lightweight cars

[Adam Wade]

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

>> 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.

> No Probs. The first full tune is not complete, but I
> am building up a pile of MS for other BECs as soon
> as I have moved house, so this summer should
> see a number running.

Great.  My third book is going to be a pratical
performance enhancement and tuning book, and it will
include retrofitting (from sourcing components to
making a base table to work from to actual
fine-tuning), so your experience in the matter would
be of great assistance.  I'll keep in touch.

> we are approaching from different angles I think. My
> fault for use of the word 'acceleration' in my first
> post. If you are not accelerating (TPSdot=0, VSSdot=
> 0) then you can tune lean of stoich. If you open up
> the throttle then VSSdot becomes positive and you
> need to go richer to get the wanted kick in the
> back. The dyno would tune for best power, so you
> wouldn't necessarily have this transition to worry
> about.

That's a thought.  However, if you tune for best power
at cruise, you will cruise at a smaller throttle
opening for a given engine speed, and less fuel. 
Likely you can get somewhat better cruise efficiency
from running lean of that (although I still believe
the true gains come from running WAY lean of that
point), but to what degree?  Enough that it becomes
worth the actual effort?

I suppose what might make more realistic sense would
eb the ECU having a best power map, which would be
used for high-load cruise and non-cruise situations,
and the ECU using closed-loop mode for cruise; then
watching TPSdot to allow switching between the two. 
To my mind, that's not the same as using a VE table in
concept; rather the opposite.  Instead of thinking of
it as enrichening when accelerating, I think if it as
leaning when at cruise, and returning to "normal" the
rest of the time.  IOW, I think that a best power map
covers 90% of the needs of a light vehicle with good
power/weight and a low reciprocating mass drivetrain,
and more like 95% of those needs if very good cruise
economy or cruise emissions are not a requirement.

> Also in a port injection setup the accel shot is
> less related to atomisation changes than with a carb
> or TBI setup.

Agreed, which is one of the big advantages of port
injection.

>> 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.

> Still reckon this is more due to throttled volume
> than mass, but need to think some more.

I think I understand what you are getting at here. 
However, something to think about...  Is not the
throttled volume of a 1000cc v-twin the same as that
of a 1000cc inline four, at the same rpm?  And yet
cracking the throttle the same amount creates notably
different demands on the fuel map (and by "the same
amount" I mean increasing the amount of airflow by the
same amount, not opening the throttle the same amount
(which would obviously be different due to the
different sizes of throttle bodies)).  If I am reading
you correctly, that goes against what you are
implying, does it not?

> <Snip from other mail>

>>> 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

> Might be terminology, and I only have experience
> with 1 engine and that was in a car rather than a
> bike, but comparing tuning that with my rotary, if
> the tune was lean the rotary just died on throttle
> opening, no drama. If the blade was too lean it
> bucked like a bronco, and in fact bent the engine
> mounts on one occasion. That may not be 'bog' in
> your dictionary but a higher mass flywheel would
> have masked this.

Well, the less mass the engine has, the more impact a
given amount of bogging will have.  So, yes, a bigger
flywheel will mask the issue better, but it will also
make the problem of actually being lean WORSE, since
keeping the engine from accelerating as quickly will
drop the airspeed more during the transition after
opening the throttle, and cause poorer atomization and
more fuel fallout from the intake airstream,
especially at lower engine speeds (which is where
airspeed is going to be lower in the intake tract at a
given throttle opening).  I was speaking strictly of a
lean condition that either was a huge power deficit
over expected, or caused a lean misfire as well, not
the observed effect on engine vibration or delta rpm.

=====
| 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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