[Diy_efi] Importance of TPS with lightweight cars

[Adam Wade]

--- bill.shurvinton at nokia.com 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. 

> But pumping losses make that less efficient than
> more throttle and leaner. However I have to find the
> lean limit for my setup first. AS you say whether it
> is worth the effort is another question, but one I
> want to answer.

Indeed.  Did you read the (rather controvertial)
article I posted here some time ago from a long-time
pilot on running extremely lean, and the EGT falling
to below rich of best power running, AND getting
improved fuel consumption?

>> 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.  

> Certainly the GM hacs I have looked at do this, with
> an added WOT enrich, so its known to work. Maybe I
> should stick with NGW until I have a lot more data
> logged on the car.

It sounds very much like "standard" thinking with a
cat and closed-loop, only perhaps taken even leaner
(I'm sure we're all aware of the extremely narrow
range of AFR in which a catalyst will operate).  And I
see no flaw in your approach, I'm just curious as to
the effort necessary and the improvement made by going
to those lengths.  I may be surprised at the
difference!

>> 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?  

> Don't think so. Certainly looking at inline 4 bike
> engines, they are direct to head with the throttles
> only a couple of inches from the heads. Doing very
> rough volume sum would suggest that this is perhaps
> only half the swept volume. Most car installs have

*cut off*

I lost the end of that...  I understand that cars have
more volume between throttle plate and valve head, but
I was comparing a two-cylinder bike engine with a
four-cylinder, and there are definite differences in
fuel consumption and mapping between the two at the
same rpm (and thus the same volume of air consumption
per unit time)...  That was more my point.  Perhaps
that's not down differences in reciprocating mass, though.

=====
| 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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