[Diy_efi] Importance of TPS with lightweight cars

[Shannen Durphey]

Adam Wade wrote:
> 

> 
> 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?
Often, yes.  It's easy to see a 4 to 6 mph gain on the highway by
"switching" in and out of lean cruise mode.


> 
> 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.
Now you're starting to talk about automotive tuning for the street.


> 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.  
Consider it as a three mode approach.  VE table provides correct numbers
for stoich operation.  Power Enrichment mode adds fuel and spark for
power mode.  Lean cruise mode provides for situations where less than
stoich operation is acceptable.  Additionally, the VE table can be
considered for conditions where leaner than stoich operation is
permissable, and there's a possibility of shutting down injectors during
completely during coastdown periods.

> 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,

Better to say "covers the needs of 90% of the vehicles..."  Subtle,
maybe, but allows one to preclude rockcrawling Jeeps and 427 Cobras.

Shannen

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