| Re: [GMCnet] Jim Bounds interesting recent posts [message #325922 is a reply to message #325912] |
Fri, 10 November 2017 12:03  |
Richard Denney
Messages: 920
Registered: April 2010
Karma:
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Senior Member |
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Jerry, I don't want to open a can of worms, but the longevity of the FITech
unit, with its electronics in a sometimes very hot throttle body, has been
questioned. One of the coaches you sold had a FITech system and suffered a
sudden fuel delivery failure for the new owners on their trip home. What
was the final diagnosis of that failure? There was speculation at the time
about effect of heat on the electronics.
I'm attracted to the FITech for that inevitable time when I lose faith in
my carb and have to send it off for rebuilding. I like the relatively
simple installation, which fits with my sharp limitations on tinkering
time. Until then, I have a good mechanical temperature gauge and if my
engine ever runs hot, it's keeping that fact a tight secret. I did not see
any evidence of overly lean running when I pulled the plugs during my
recent (preventative maintenance) engine replacement.
I recall (probably inaccurately) comments from Dick Balsley from years ago
that lean running and even detonation are not problems at part throttle.
The question is how much we are opening the throttle for given conditions,
and is the power enrichment feature kicking in early enough? That led to a
discussion of power valve springs at the time. He said Rochester designed
for richness to overcome the manufacturing tolerance in the carbs and to
overcome the variation in mixture caused by intake manifold passages. The
number 15% comes to my mind as being the target (6% for the carb itself),
which means a design AFR of no more than 12.7 during power enrichment (when
it is critical), to ensure that all air has fuel to burn instead of metal,
even with pure gasoline.
Does an O2 sensor average the reading across all cylinders? (And it only
reads one bank.) If so, I would want it 10% rich just to keep one cylinder
from leaning out at WOT as a result of intake mixture variability.
Rick "may be remembering this wrong" Denney
On Fri, Nov 10, 2017 at 10:59 AM Gerald Work wrote:
> I have followed with interest his comments about why carbs no longer work
> (todays gas won’t vaporize correctly for use in a carb) and now why our
> engines are blowing up mote frequently (they run too hot under some
> condition).
>
> Take a look at the presentation I did on Fitech (
> http://www.bdub.net/FiTech_is_the_Real_Deal.pdf). Near the end are two
> important slides that I think help explain what he is saying. The slide
> with the two charts is very telling. Those charts are based on an engine
> running pure gasoline with a stoichiometric air/fuel ratio of 14.7:1. One
> chart shows peak power at an air fuel ratio of around 12.5:1 (quite rich)
> while peak economy is around 16:1 (way too lean for our engines to survive
> for very long). Those charts are based on UNADULTERATED gasoline. The
> curves for gasoline laced with alcohol would look much differently.
>
> ...
>
> Jerry
>
--
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com
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