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Regraph Electronic Distributor

Hi Folks

Would like to ask about electronic distributors.

My old man went and changed over our old points with an electronic ignition (as usual he is not sure what brand but reckons it is a Chevy ignition.) By the way the car is a HZ 308.

The car has now got real bad low rpm power....just seems so weak and sluggish. I have read that all ignitions have different curves so I have no doubt the igntion I have needs re-adjusting.

Can anyone please point me in the right direction. Would love if someone has a manual or specs that show the appropriate curve specifications. (Prefer to work on the car at home)



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mate you'll have to rip the

mate you'll have to rip the dizzy out and take it to somewhere that regraphs them you'll need your cam and engine specs as well as it helps to know your compression. i strongly recomend getting it done though as it changes the whole car.

electronic ignition woes

Is the coil getting the full 12 volts as electronic distributors require this to work correctly.

If it is still getting the reduced voltage as standard for points distributors then it may well produce a weak spark which may be some of your problems.

Did he use a relay or run a new wire for the electronic dizzy?

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Spark Plug Gaps

I bet he didn't open up the spark plug gaps. HEI needs 1.5 mm. The
original 1.0 mm will bring the car to its knees since HEI has
a much shorter duration than the original IDI.

Check to see what plug gaps the new ignition wants.


Shorter duration?

Last time I checked, a red motor points system had about 1.2 milliseconds spark duration at idle and a blue motor HEI about 2 milliseconds. That's with the HEI using the proper 1.5mm plug gap too; with a 1mm gap the duration goes out proportionally longer. A short spark duration does bad things to exhaust emissions so it's unlikely a HEI would be like this given part of the reason for it being introduced at the time was to smarten up an engine that was being slugged with exhaust gas recirculation and lean mixtures. What figures have you measured?
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V12's etc


That which was published at the time. Maybe you want to re-check it.

I remember a very lengthy thread where people who had never tried it
claimed that a gap less than 1.5mm had no effect on HEI. Are we headed
for that loop again?


HEI spark duration

You say that a HEI spark has short duration. How short? Lets have some numbers. I'm sure you know Lord Kelvin's famous quotation...
BTW, big plug gaps are good - no argument there. Mine are a full 2mm and the spark current of my home-made ignition is 90mA compared with 60mA for the standard HEI. I use an 85:1 E-core coil instead of the normal 100:1 and a primary current of 7.67 amps instead of 6 amps. On the basis of the primary current the energy is 63% greater than a HEI.
me shed...
Best cruise song ever
V12's etc

1 mm

Cool Mate. What's the duration of HEI under a 1 mm plug gap?


1mm gap duration

I'd have to pull out and re-gap the plugs to find out, so what I'll do instead is make a setup on the bench and record the duration with 6, 8, 10, 12, 14, 16 mm gaps which (very) roughly corresponds to 0.6 to 1.6mm gaps at 150psi compression. Not the last word in accuracy of course, but it will give a reasonable idea of the trend.
me shed...
Best cruise song ever
V12's etc

HEI Secondary Duration

I'd appreciate you posting your results.

It's true that I don't own the sophisticated test gear that you do so I can't provide figures from my own cars, only those that can be
measured from a handheld digital multimeter.

Even though the above sounds primitive, I do have a degree in Electronics and Communications so I can draw sound conclusions from observations.

I've also worked from the published results of Electronics Australia,
Electronics Today International and Silicon Chip.

Because those publications were stating the duration to be shorter
I never challenged it. Those guys so often published the waveforms
that supported their findings and they got flounced by the public
if they published incorrect data. The figures also seemed consistent
with an ignition system that was a hybrid of CDI also known to have
short secondary duration.

I've posted before that for some time I ran an original oil filled
Bosch HEI coil biased down to 7 volts and triggered by an EA dwell extension circuit because HEI was prohibitively expensive at that time. Since dwell extension forced the coil into saturation and held
it there for extended periods, its output duration was very long
though its output voltage was reduced. As a result the coil plus dwell circuit could only run 0.050" plug gaps, but did so superbly.

Later I triggered the same coil from the standard Holden Bosch HEI
module direct powered from 12 volts. Sparking into 0.050" gaps
gave horrible performance, far worse than standard breaker point
performance from the same car.

The only change I made then was to increase the plug gaps to 1.5mm
(as per the spec) and the results were superb.

Acting on the information at hand it appears that HEI does not permit
saturation of the coil former, maybe in the interests of extending
the coil's life which is a definite part of the module's charter.

If you trigger an HEI coil by flashing it across a 12 volt battery
I would expect it's spark duration to be longer than if triggered
by a module, since the module will current limit and the open flash
will allow an unrestricted current to flow through the coil primary.

It's exciting to see the trend in lower impedance coil primaries,
a vital aspect of increased secondary energy. With modern trasnsistors
these are easy to support.

If reduced secondary duration was not the cause of the power decrease
I saw it would be good to know what aspects were at work especially
since you can observe the waveforms. Like so many turn of the turn of
the 20th century inventors that I admire, I mostly have to work with
pure reason and published results coupled with trial and error.


HEI module

Quoting T:
"Later I triggered the same coil from the standard Holden Bosch HEI
module direct powered from 12 volts. Sparking into 0.050" gaps
gave horrible performance, far worse than standard breaker point
performance from the same car."

Did you trigger the module from points (square wave) or from a magnetic reluctor signal of a HEI distributor? To achieve proper dwell control the module relies on both the increasing voltage with rpm *and * the shape of the waveform from the trigger coil. And not just any old distributor will work with those modules either - they are somewhat fussy. Their internal function is not unlike the Motorola MC3334 ignition IC --> link.

me shed...
Best cruise song ever
V12's etc

Magnetic Pickup

I triggered the module from the HEI distributor and its magnetic pickup.



He will need to change the plugs as well to suit the larger gaps,,
try advancing the timing as well, sounds a bit retarded,,,,

Silence is Non Committal


yeah like above said, must have 12 volts going to coil,
use blue motor spark plugs,
for best results put your vacuum advance from the dizzy to the intake manifold( not carby) set your timing to about 8 degrees adv. with the vacuum hose off (plug up manifold hole at this point), then when you put the vacuum hose back on at idle, the timing on the engine shold read about 26 deg adv (at idle) this is the best way to run a street engine.
if your car is still gutless down low, then the harmonic balancer may have twisted so it is showing a false timing.
if you suspect this is the case advance the timing on idle a further 10 or 15 deg, if it then improves it means the balancer has indeed twisted. so get a new one. hope this helps

changing dizzy

Have you changed the coil to a high energy coil?Grab one off a blue motor Stateman or Commodore and also re-wire .The factory wire to has inbuilt resistance.It will run with the standard plugs but will run better with 1.5mm gap.Good luck....George.

Electronic Ignition

I have a HQ GTS (253) with electronic ignition fitted.

I run 1.5mm plug gaps (now) but ran the standard 0.9 gap for several years.

I personally have not noticed an iota of difference in performance, fuel efficiency etc.

I have had had advice recommending both gaps but to me it doesn't seem to matter.

However... my 253 is getting quite tired and is not a spirited performer by any means, so it may not have been the best test bed for a comparison.


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If your V8 powered car is carrying a 6 cylinder diff and cooled by
a mechanical fan, it's likely you wouldn't notice a difference
because the vehicle would already be needlessly bailing heaps of fuel
overboard. Sort of like driving around in 1st gear.

Running with reduced plug gaps may have filled up the piston ring grooves with gunk, a consequence of wet combustion.


0.9mm vs 1.5mm

The biggest difference I noticed is smoothness of idling and if on petrol, when cold it was way less likely to stall. Power is a lost cause with my car :-P It lets me run my gas mixture super lean without running rough for slightly better economy. On gas the last 2 tanks I got 18.06 mpg and 18.15 mpg around the suburbs. 202 HJ Trimatic.
me shed...
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V12's etc

Dizzy Total Advance

Will try a few things to see the difference.

I know there are things to consider before adjusting timing (ie. cam, compression etc etc) but roughly how much mechanical advance is required and within what rpm range for a red 308. (obviously this would be going on the original figures)

plug gap

So i went from .9mm to 1.5mm and noticed the engine idel is heaps smoother. Aint driven it yet, but seems to rev quicker too.
First time ive tried this exercise.
Im running a crane HI6 too.
Trenton's Email

Pulg Gaps

So was the consensus to use Blue Motor plugs too? Are they different.

Obviously 1.5mm gap seems to be the preferred setting too. I'll pop that in the memory banks.

When the GTS is rebuilt the 308 will be running electronic so I'll need to revisit all this info when that time comes.

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HQ GTS rebuild pics

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Are they different

Blue motor plugs have a tapered seat. I can't remember if red motor ones do, or not. But make sure you have the right seat on the plugs to match the seat in the head. Also, we ran a mates 253 VB (VC electronis ign) with 1.0mm gaps and it had bad mid range power and crap idle, stalled when dropped into drive when cold, etc. With 1.5mm it runs like a dream.

Tapered plug seats

I didn't know that. Hopefully I'll remember it. lol

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red or bue plugs

Dont the blue motor plugs have a R on the end of the part number.
I was told R was resistive.
I used VH 253 plugs in my old red 253, i didnt buy them, but they looked the same, and ran fine on the bosch electronic.
Both red and blue head v8s are tapered seat.
I want juicy spark to ignite 10:1 on a 355/308 stroker with a big cam.
I also have spiral wound wire leads to assist.
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blue motor plugs

Vc-VK 5.0L plugs are 44TX. I'm not sure about this R that you mentioned.
Blue motor plugs will run fine in a red with electronic. Because that is the ignition they are for. The electronic ign came out on the blue motor.

plug types

I have complete listings on most brands to decipher all the letters and numbers if anybody requires them,,,,

Silence is Non Committal


Can you tell me if been fed some [Naughty Pottyword] on 'R' bit. I refer to NGK plugs to suit a blue 253 engine. I dont know the complete part number.
Can you also recomend a spark plug to suit red holden v8 which supports a bigger gap then 1.5mm. I currently have NGK BP6FS, and when i open the gap to 1.5mm, it looks weird. Accordingly to my manual, my ignition my support a larger gap. Its a trial and error thing.
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sparkplugs holden 253/308

253 blue motor i'd use BP4FS or BP5FS or Champion BL-15
RED motor i'd use BP6FS, you don't have to increase the gap too much, even with electronic ignition set around 1mm is fine

NGK plug numbers

first letter = thread and hex size:
A=18mm thread, 25.4 hex
B=14mm thread, 20.6 hex
C=10mm thread, 16 hex
D=12mm thread, 18 hex
F= 7/8"-18, 23.8 hex
G= PF1/2"-14 23.8 hex

Second, third letters = prefix for special construction feature:
B= hex 20.6mm
C= hex 16mm
G= hex size 23.8mm
L= compact type (shorty)
M= compact type (bantam)
p= projected insulator
R= resistor type
S= shielded type
U= surface discharge type

First number = heat rating number
Eg. 2 = Hot
through to 14 = cold etc

First letter after numbers = suffix for thread reach
none= 12mm (thread dia.-18mm)
" " 9.5mm (thread dia.- 14mm)
" " 22.5mm (thread dia.-PF1/2"-14)
" " 16mm (thread dia-7/8"-18)
L= 11.2mm
H= 12.7mm, racing type 12.5mm,,
E= 19mm, racing type 18mm
F= conical seat type
"A-F= 10.9mm
"B-F= 11.2mm
"BM-F= 7.8mm
"BE-F= 17.5mm
Second letter after numbers = suffix for construction feature etc
A= specials
B= special plug for Honda vehicles
C= competition type
GV= racing plugs, centre electrode of precious metal
N= racing plugs, nickle electrode
R= shielded resistor plugs
S= copper core centre electrode (super)
V= centre electrode of precious metals
W= tungsten electrode
X= series gap plugs
Y= 'V' grooved centre electrode
Multiple ground electrodes types
and there are specials of L,Z etc
finally, a set of numbers is used at the end to denote wide gap, eg 11, 12, 13, 14, 15 etc
Plugs for a blue 253 should be BR5FS-15,,
B= 14mm thread, 20.6 hex
R= resistor
5= heat range (one range hotter than 6)
F= conical seat
S= copper core
15= 1.5 mm gap
Now these listings are as when the blue motor was new(20 years ago), so some may have been superseded by now,,
There is no listing for a wide gap non resistor type plug in my books,,
A resistor type with wide gaps would not operate correctly on a points system,,,,
I have these listings for champion, and bosch as well,,,,


Silence is Non Committal

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