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Wed, 01 June 2016 09:12  |
fbhtxak
Messages: 191
Registered: April 2006
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Randy,
A fine contribution to the owner community.
'Especially timely for me as I migrate from carburetion to the Howell EFI
system packaged by Jim K. .
'Regards,
Fred
Fred Hudspeth
1978 Royale (TZE 368V101335) - Tyler, TX
1982 Airstream Excella (motorhome) - Cooper Landing, Alaska
Message: 12
Date: Tue, 31 May 2016 19:17:30 -0600
From: Randy Van Winkle
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] More on FiTech questions
Message-ID:
Content-Type: text/plain; charset="utf-8"
glwgmc wrote on Sun, 29 May 2016 14:16
> Hi Gordon,
>
> Letting the ECU control spark seems to be popular with people who are
confident they have a reliable knock sensor installed in a location that can
> properly distinguish between pre detonation and other engine noises as it
allows the system to dial in more advance under certain situations. To do
> so without a properly working knock sensor would be very risky to the
health of the engine. By advancing more it appears to be possible to wring
> out one or perhaps even more mpg.
I have wanted to chime in here to clarify some of the misconceptions of how
knock sensors (KS) are used in our application. The implications from
most are that without a proper KS (and one was never engineered for the 455
or 403) you should not let the computer control the spark advance (SA). I
think that is a false assumption and should not hold anyone back from
desiring or proceeding with using a computer controlled distributor or our
engines. There are several reasons for implementing an electronic fuel
injection (EFI) system for fuel management. It precisely meters fuel under
all conditions: cold starts and warmup (minimizes washing down of cylinder
walls); altitude changes; immediate start-ups; immediate shut downs; higher
pressure in fuel lines minimizing vapor lock (if pumps are installed
properly). There are many excellent solutions for doing just fuel
management:
FiTech, MSD Atomic, Holley, Meqasquirt, FAST, Howell with EBL, each with
advantages and disadvantages but most do an excellent job of metering fuel
with self learning capabilities (either automatic or semi-automatic). In all
cases, I think one will "feel" an increase in responsiveness over a
Q-Jet. The amount of "feel" will probably be determined based on how well
the Q-Jet is tuned. I suspect there are not many Q-Jets that are tuned to
their optimum due to age, wear, etc. However, a well tuned Q-Jet will
perform similarly to a fuel management only Throttle Body Injection (TBI)
system and probably won't see too much difference in fuel economy. In fact,
I don't think you can do too much to get better fuel economy because it
takes fuel to push a 12,000 pound vehicle with a large frontal area through
the air).
Most EFI systems, even the early ones back in the 80s, also controlled
spark. Why? Partly to help meet emission standards, but, also, for increased
performance. Most early implementations used KS as an added safeguard for
the engines. Early KS implementations did not provide full protection for
engines simply because the technology and engineering was not that
sophisticated. Modern day KS implementation and Computer Controlled Spark
does a
great job, and, in fact, can detect excessive knocks when using lower octane
fuels and will allow the engine to run with less than recommended octane
without excessive damage (although not recommended).
I'm hearing people say they wouldn't run a computer controlled distributor
on our engines because the KS sensor is not engineered for our engines and
cannot protect the engine. By the same token, then you should not use a
mechanically controlled distributor because there are absolutely no
protection
for the engine other than how good your hearing is. When I tune an EFI
system that also controls the spark, I tune in much the same way you would
tune
a mechanically controlled distributor. I have a couple of known good spark
tables (spark curves if you will) that I start with. Depending on how
aggressive someone wants to be, I then increase the spark until the KS
starts showing me some knocks in certain cells. At this point, I don't rely
on
the KS to continue to "protect" the engine, but pull out SA in those cells
were knocks occur. It actually takes less SA retard to prevent knocking
than it does to stop knocking once started. So what is done with a
mechanically controlled distributor? You either use a very conservative
initial
spark advance setting with a timing light or if you want to be more
aggressive you increase the initial SA setting. Then, if you hear knocks
(pinging)
when under heavy load you pull over to the side of the road and retard
timing by twisting the distributor to retard SA. You now have effectively
retarded spark by let's say 2 degrees across the complete spark curve. When
I'm tuning SA on an efi system, I have up to 200 cells in which I can
advance or retard timing. Typically, our engines are knock limited only
when under heavy loads and that affects anywhere from 6 to 12 cells. I can
change those to eliminate knocks and keep the other cells at an optimum
setting for performance and fuel economy. It is the spark that can allow you
to steal a couple more mpg in some cases (there's no guarantee in claiming
better fuel economy with EFI because there are lots of factors involved
with the health of an engine).
Bottom line is that I don't rely on the KS to continually notify the
Electronic Control Module (ECM) that spark needs to be retarded but, rather,
use
it as a tuning tool and a protection mechanism if something happens to the
engine that causes knocks to start occurring when previously there were
none. This can be caused by getting a load of bad gas, something causing
hot spots in the cylinder, a spark plug failure, etc. On my engine, I
usually see the display monitor showing Knock counts at about the same time
that I start to hear some slight pinging. The ECM reduces SA in 4 degree
increments until the knocks stop then reintroduces SA until back to what is
commanded or until new knocks occur. These changes are instantaneous I
believe that saved my engine when I had a spark plug that failed. With a
mechanically controlled distributor, I may have lost an engine. Also, the
ECM has SA adders and subtractors based on various conditions (sensors
inputs such as coolant temperature, inlet air temperature, change in
throttle
position (delta measurement), change in vacuum (measured by MAPP sensor and
is also a delta measurement), etc. These all can mitigate the chances of
knocks.
So, KS is a tool, not perfect in our application but good for tuning and
good as a backup "protection" mechanism. Just as in the 80s and early 90s,
the KS was not perfect but used as a backup "protection" mechanism.
If anyone is not installing an efi system solely because they are concerned
that a KS will allow damage to their engine, then hopefully this
discussion will dispell that notion. Sorry to be so long winded, but these
discussions are difficult in just a few words.
--
Randy & Margie
'77 Eleganza II '403'
Battlefield, MO
------------------------------
Message: 13
Date: Tue, 31 May 2016 20:01:13 -0600
From: Randy Van Winkle
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] More on FiTech questions
Message-ID:
Content-Type: text/plain; charset="utf-8"
gibsongo wrote on Sat, 28 May 2016 14:04
> Jerry
>
> I really appreciate your posts on installing a Fitech in one of your
coaches - comments like this plus the fact that I was going to have to bear
> the cost of buying a rebuilt Quadrajet to finish off my coach were what
prompted me to go the Fitech route.
>
> Full disclosure - although I have rebuilt old cars and motorcycles, my
mechanical knowledge of anything more modern that the mid-60s is sorely
> lacking. But rest assured - I am having the FI installed by a
professional.
>
> I specifically chose the 600 based on the understanding that the FI's
computer module would control the spark advance of my "pointless"
> distributor. Do I understand that according to Fitech, most of their
customers stick with good old mechanical and vacuum spark control? And if
this
> is the case, any reason why? Is this what you did as well?
>
> Thanks
>
> Gordon
> 1976 23' Norris Upfit
> Montreal West, Quebec, Canada
According to FiTech documentation, timing control cannot be used with an HEI
Distributor. It is not clear to me if there is a distributor that could
be substituted on an Olds engine to allow computer control by the FiTech
EFI. If it cannot control spark on the 455 or 403, then I would see no
reason to get the 600 hp efi unit. The 400 hp unit would be adequate and
costs less. I have also seen references that you can pin the mechanical
advance plate and get the HEI to work. I would think FiTech would not say
HEI was not supported if this were possible? Looks like you could install
an MSD ignition system and get this to work.
However, They only have a 3x3 table to control spark so I would be concerned
if you get much benefit to letting the EFI unit control spark. I'm
guessing you can command Spark Advance (SA) for 9 points and it then
extrapolates those into a spark curve. Maybe slightly better than an HEI
curved
distributor but not by much. Most early GM TBI EFI systems had up to 12 x
16 cells for SA (more for higher RPMs than in our applications).
Interesting to see how computer controlled spark actually works/performs for
our application?
--
Randy & Margie
'77 Eleganza II '403'
Battlefield, MO
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