Chris wrote about run-on problems. Proper engineering term is
"auto-ignition" but no matter we all know the term run-on or deiseling.
It is caused generally by the engine being a bit overheated and in
combination with TOO HIGH idle rpm!
If all other factors are normal, the way to prevent it is to first allow
the engine to lose some combustion chamber heat via a few seconds idle time
before switching off.
Second...get that idle rpm down to a proper speed at moment of shut off.
This means to be at around 850 rpm on stock engines at low altitude.
If for ANY reason you cannot get a slow enough idle rpm then just put the
tranny into 4th gear (or if an auto, use D) and cut the ignition while
easing up the clutch a bit to drag down the rpm. With race cams requiring
higher idle rpm this is indeed std. for such cars.
A device which would pop open the manaifold at shut off would indeed kill
vacuum and stop the fuel pull over which these CD and Zenith carbs are
prone to. However, such a micky mouse rig is totally unnecessary if the
basic idle rpm is correct and slow enough, or if this "drag" method of shut
off is followed.
In some cases, there will be found to be carbon deposits in the chamber
which are glowing while the engine is running (even at idle). Such a
condition provides an ignition affect like a model plane engine glow plug.
We have found that letting the engine idle 10-20 seconds reduces the glow
to a minimum, then as you switch off, open the throttles fully.
The large amount of cool air inhaled will tend to quench the glow spot and
usually results in a clean kill.
If no luck....revert to the clutch drag in 4th gear.
-------------------
Bill Lewis wrote on his overheating with the quad row core he installed.
From the tests done it appears there is a lack of air flow at idle and this
would indeed be expected for an unshrouded core.
Deep, multi row cores require high air speed against the forward face in
order that the air molecules dont become so heated (as they flow through)
that they are too hot by the time they reach the last row of tubes and
fins. For race cars and aircraft, we can use some very thick cores because
the vehicle is never expected to encounter slow air speeds.
Passenger car cores of 2 or 3 row design do not require any suplimental fan
action if the air flow is approx. 15mph or higher. With a 4 row core you
simply need a bit faster air flow in the region of say 18-20 mph through
the core. The stock fan, at idle rpm likely makes around 15-16mph through
the core and if you happen to be facing the wind, then it's speed it added in.
A simple shroud should do the job as you already learned.
However.......I come back to basics as usual! If the radiator is truly
known to be CLEAN, the pump action normal, engine timing normal, water
passages KNOWN to be clean and normal....Then...there was no need to
install a 4 row core in the first place....unless you have a increased
output engine which just might make more heat losses than a stock core
could handle.
On the race engines which pump lots more BHP than stock, we do use a 4 row
core without fan, but then we do not idle this engine for long and we also
use a 15psi cap as well as having screw retainers acting as safeties on all
core plugs in the block and head. We also race with a 60/40 ratio
water/antifreeze mixture in order to obtain a bit more heat transfer than
50/50 would give. A specially modified stat is used to give us 215 deg.
coolant temp. as this is worth about 8-10 BHP (for free) on the dyno.
The engine has no problems running at this coolant temp and with a big oil
cooler radiator in place of the dinky stock series V oil cooler, we can
keep oil temp below 240 deg. on a 90 deg day and we accept oil temp of 250
deg on a 100 deg day. Oil which has seen over 250 deg is never reused
after the race. Enlarged oil pan is used and this has internal baffles to
minimize side slop in curves. This big pan and large cooler increased total
cap. to about 7.5 quarts.
The car ran it's last events under my ownership in about 1992 and finished
up in the vintage car class (Rocky Mt VCC) with a record of 17 first places
in 21 starts. Trying to finish first overall and catch a fast AC Cobra,
the engine threw a rod at 8100 rpm. It has been rebuilt and then sold to a
chap in CO but I don't know if he runs it as he also has a Bug Eye which he
does race.
--------------------------
Jarrid, your comments on ignition points are good but I offer the following:
I left out lots of little things due to space and time. Pits on the points
are NOT enough reason (IMO) to change points. I like to dress down a rising
pit on the grounded point, when it is first observed, then I test the
condenser mfd. and replace it with a condenser having about .05mfd less
mfd. capcity. If the grounded point is developing a hole not a rise, then
you install a condenser with more capacity. When this is done correctly,
you would have a condenser perfectly matched to that cars system and the
points last forever with no pitting at all.
Condensers have NO KNOWN LIFE SPAN. Putting in a new one might result in a
failed cond. the next day...who knows. I like to stick with things which
are known to run normally and an old cond. seems as reliable as a new one.
Back in the days before electronic ign. a certain number of new cars failed
to drive off the line every day due to cond. failure!
Your remarks on ign timing are all correct. Mixture, compression and octane
as well as chamber changes and piston crown mods. also influence flame
travel and ultimate timing settings.
I would like to defend the 36 deg. instructions for stock or semi stock
engines by pointing out that a 11 deg or 13 deg advance wt. would of course
give 22 and 26 deg of cent. advance and taking this away from my 36 deg.
would leave the engine having 14 or 12 deg BTDC at idle. This is a tad
high for some engines since 10 deg is the std suggested setting.
I actually grind off the stops on the cent. wts. so as to obtain 14 deg adv
(=28 on crank) because in northern states where you have zero or sub zero
starting temps, these engines will crank faster and light up faster when
set at 8 deg on the crank pulley. The modified 14 deg wts. still are then
set to provide 36 deg at full revs.
If you have some sort of 3/4 race cam (or more) and possibly some really
high C.R. then the engine has to be power timed at high revs and full load
and the determination made as to just what degree setting gives it's full
HP short of knocking.
As a point of interest to all......when a cylinder is detonating (knocking)
such as can be sustained on a long hill or grade...the piston crown temp.
goes up approx 100 deg. per minute ! The melting point of cast aluminum
will be reached in approx. 4-6 minutes depending upon amount of heat at the
start and the degree of knocking being created. Forged pistons can handle
around 120 deg more than cast alloy. Momentary knocking such as when
accelerating through the gears doe not raise crown heat any measurable
amount but takes a toll on top piston ring lands, which pound down and
eventually cause comp. loss and other ill affects. Then of course knocking
is harsh on rod bearings as well. It's like an overweight smoker who is
also a heavy drinker! Something is going to fail eventually and this guy
goes by the nickname of LUCKY !
Dick T.
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