[Amc-list] AMC Six ignition timing

[Tom Jennings <tomj@xxxxxxx>]

SO WHERE WAS I!

Sheesh.

It's been a month since I posted I think! Projects, some
travelling and a lot of work!

So I have been experimenting with ignition timing curves with
the '83 258 in my 1970 Hornet. Some pleasant surprises!

The short answer: with a small amount of effort you can run A
LOT MORE timing on this engine than the stock settings.

I am running a total of 34 degrees advance (static+centrifugal),
89-octane gas. The factory spec is something like 20 - 24 degrees
-- 6 - 10btdc static (depending on year) and 17 or so mechanical
(centrifugal) advance in the distrib.

Advance, pinging, fuel octane and coolant temperature are highly
interactive. 87 (crap gas) to 89 octane makes a huge difference
in ping variability, more on that below, but for the last few
months I've just run 8i9 octane to minimize it.

Coolant temp and advance setting and pinging are tightly related.

* Retarded spark increases head (coolant) temperature (hot
   gases out the exhaust instead of pushing the piston down).

* High coolant temperature increases pinging (need to retard
   spark).

(I suspect, and will experiment with, makin my secondary jet
one notch too rich to see how that affects near-WOT and WOT
performance vs. pinging.)

Pretty much, I got the cooling system under control and I was
able to crank 34 degrees total advance. We'll see what happens
when it gets really hot out; I may have to retard it a bit,
I'm guessing to 30 - 31 degrees but measurements will tell.

COOLING:

I have a "new" engine and a new 3-row radiator and two electric
fans with a thermostat glued to the top tank.

I never really thought about the cooling system details (but the
devil is in the details!). I used a real electronic thermometer
(I wrote about this before). I have a 190 degree Mr. Gasket
thermostat; it starts to open around 170, and is fully open at 190.

I always thought (wrong!) that they opened at the rated temp, so I had
my fans come on at around 190. Big mistake! The coolant temp went low
(170 - 180) on the highway (lots of air) then ran around 190 - 200 in
town.

So with middling timing settings (factory --> 30) it pinged in
town, but never on the highway. It was hair-pulling frustration to set
the timing by ear.

So now I have the fans come on at 175 - 180 (or so, it's in my
notes in the lab), the in-town temp never rises above 180. Slight
pinging under hard accell after bumper-to-bumper then pulling
onto the freeway hard, but it disappears within a minute.


Oh yeah, with 30+ degrees of advance the motor PULLS LIKE HELL!

(My mileage however hasn't improved; I record every single fill up, my
average for 2006 was 18.7 Jan to Dec. It was 19 for the first half.
My carb is very old, and not rebuilt in over a year/25K miles.)


The summary:

For the AMC six:

* good cooling system!
* 190 degree thermostat
* electric fans come on at 175
* *thoroughly*! rebuild a duraspark distributor
* get a Ford recurve kit, tweak adv to come in by 2800 or so
* set or get mech advance unit that does 20 degrees
* set static to 10 then set by ear


PS: With vacc. advance unit, yes, on highway light cruise you
have nearly 50 degrees total advance. That's correct and as it
should be!
_______________________________________________
Amc-list mailing list
Amc-list@xxxxxxxxxxxx
http://www.amc-list.com/mailman/listinfo/amc-list