Re: more questions about my elec.ign swap

[Doug Ahern <D170A833@xxxxxxxxxxxxxxxxxxx>]

[AD removed for archives]
-------------------------------------------------------------------
Sign up today for a No Annual Fee Discover® Platinum Card and get?
0% Intro APR on Purchases & Balance Transfers for 8 Months, Up to 
2% Cashback Bonus® reward on your purchases & 100% fraud 
protection.
caadlRMbOyW3Na/DiscoverCard
-------------------------------------------------------------------

On 37 04/14/05, Westerlund, Ken wrote:
> I agree with your comments on electronic ignitions; however, I do have
> one questions.  It's about the ECU brain box issue.  I have heard that
> the chrome box (I think) and some other boxes will retard the timing at
> higher RPMs.  Is that true?  Is it programmed into the box to retard
> timing at certain RPMs?

I'm no expert on the ECU units, but here's what I know:

the ECU unit's function is the following,  when the key is in the
ignition position, 12 volts is applied to the 'ign' pin, and the
ECU closes the circuit between the neg. (-) coil pole and ground 
(this is why the ECU must be well grounded),  thus grounding the
neg. (-) coil pole.   

The distributor's magnetic pickup sends a signal to the ECU as the
reluctor tooth passes the magnetic pickup and reduces the air gap 
between the reluctor tooth and the pickup.  This happens 8 times 
per rotation on a V8, and 6 times per rotation on a six (8 teeth 
or 6 teeth on the reluctor).   When the ECU receives this
signal (a very very low voltage signal,  similar to a the signal
a guitar pickups sends when the metal strings vibrates over top, merely
an electronic pulse), the circuit between the neg. (-) coil pole and ground
is opened by the ECU.  The coil's secondary winding, without a ground at 
the neg. (-) pole, causes the secondary winding to discharge a high 
voltage spark to the distributor, which of course, gets routed to a 
spark plug.  

The circuitry in the ECU is designed to be very precise.  a traditional
points-style breaker ignition, because it operates on a mechanical basis, 
has a limitation that at some particular RPM, will no longer be able to
deliver the spark on time, causing the timing to retard, and if RPMS 
continue, misfire certainly ensues (similar limitation that valve 
springs present in a OHC/OHV valve-train design).  The kind of precision
that is required in an ECU makes my comparison to a voltage regulator
(VR) a little unfair. The timing of a VR is not really of consequence
when compared  to the required timing precision of an ECU.

The ever popular and sure to make an appearance at every car show,
"Orange box" ECU is a street ECU that Chrysler specifies precise timing
up to 6000RPM.  The "race" only 8000RPM Chrome box and the 10,000RPM
Gold box go higher, but both use different transistors (and maybe other 
components as well) to ensure precision at higher RPMS but these components
runs hotter, and when used on the street, they over heat and cause
ECU failure.   There may be other functionality to alter the timing,
but I can't imagine exactly what they'd do, given their stated
purposes (street performance or race).  Retarding the timing at higher 
RPMs doesn't seem like anything a racer would want.   BTW:  you are
unlikely to find an MP chrome box P4120534 or gold box P4120600 in a
junkyard: Wells, Echlin, Sorensen, and many many other 3rd party ECU
manufacturers built OEM spec, standard ECUs in chrome, and various
different color metallic cases,,, (you'd be surprised, but I've heard
folks think they've happened upon a race "Chrome Box" in junkyard
Cordobas).

On the 1972 ECUs Chrysler toyed with a "speed limiter" function on their
production ECUs, which must have simply been a rev. limiter.  They idea
was canned by 1973, and may have even been a recall.  Lean Burn systems
may have also used "tweaked" ECUs,  but I'm not sure. (anyone know?)

ECU side items:

I know a guy that has a 63 Avanti R2 that some shadetree
mechanic, somewhere along the way adapted a Chrysler ECU unit to with
the original Studebaker 289cid engine.

a local mechanic has converted many Dakota 3.9 V6s (3/4 318) to a 
traditional 73-75 Electronic Ignition by using an autozone reman 
V8 dist., swapping out reluctors with a \6 Elec. Ign. dist, and 
adding an Orange Box and splicing in the appropriate wiring.  

[AD removed for archives]
-------------------------------------------------------------------
Is your PC running at 100%? Check your PC's health in 2 minutes!
caadlAsbOyW3Nf/PC Health Check
-------------------------------------------------------------------

----
Please address private mail -- mail of interest to only one person -- directly to that person.  I.e., send parts/car transactions and negotiations as well as other personal messages only to the intended recipient, not to the Clubhouse public address. This practice will protect your privacy, reduce the total volume of mail and fine tune the content signal to Mopar topic.  Thanks!

'62 to '65 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html. 



bOyW3N.