[ihc] Ignition - timing vs CR vs quench, Taurus fans

[Tom Mandera <tsm1@xxxxxxxxx>]

A few data points some might find interesting..

Last year, I installed a Taurus or "Mark VIII" electric fan in my 
Travelette which sports a 3-row radiator and a then-new 392.

It didn't keep up last year.  Ambient temps were hotter, and the 392 was 
fresher.  It did fine with a stock 392 under the hood, but not with a 
<900 mile "hot-rod" 392.

This year things went much better.  The load I was towing was heavier 
and taller (lifted SII on 36s, vs a stock 800 with no top last year). 
Ambient temps were down 10-deg or so most of the trip vs. last year.

This year, the electric fan had NO problems keeping the 406cid motor 
cool.  Engine temp did climb to 230 on some of the long pulls over a few 
passes.  I can't say if the temp would've kept climbing or not - I had 
to stop to let the fuel cool and the engine bay to stop being so heat 
soaked before continuing.

When I could keep enough road speed to keep the rear-propped-open hood 
to ventilate enough heat, engine temps never peaked over 230, and it 
kept the fuel cool enough to motor on at full throttle.

Didn't get HOT on the "rolling" hill climbs, either.  It did run 200 or 
so at times on long, but gradual (read: still at speed) pulls, but never 
got HOT.

To be fair to the truck, I had mild vapor-lock issues while sitting 
stopped in traffic in SLC, too.  Temp gauge read 180 or so with the fan 
on idling in traffic, but the fuel was boiling from overall heat soak 
until I had managed to go a few miles.

The fan keeps the rad cool, but does nothing for the fuel. ;)

So, at this point, it looks like the Taurus fan is a success when used 
as a replacement for the deep-shroud in a 74/75 pickup or Travelall.

Now the other side.. ignition.

When I built my 392, I decided to experiment a bit.. well, on a number 
of things.. but the item in question is "quench" and "compression."

I stroked the crank, then decked the block .036" (IIRC) which put the FM 
H996CP60 pistons at or near "0-deck" - putting the piston crown flush 
with the block deck.

This should result in a .038 or .042 quench distance comprised entirely 
of the head gasket.  Per a few websites that speak about this stuff, 
.040 is ideal.

The theory is that .040 quench will let you run more advance/more 
compression on less octane w/o pinging.  Supposedly running a little 
less compression, but .060 quench might ping, while more CR and .040 
quench won't.

Added benefit is more CR = more power, of course. ;)

With the modifications to my 392, those who know better than me put the 
compression ratio at around 9.5:1.  Sounded a *little* high to me for my 
tow motor, but it's not like I can change it now. ;)

The GOOD news is that with this ~9.5:1 engine I'm running a points 
distributor with a Pertronix Ignitor, and I set the static timing at 
12deg BTDC before I left.  It seemed a little much to me, but I thought 
I'd try it and back it off if I had problems.

Stock coil w/ resistance wire (9V), NAPA 7mm wires, Autolite 85s. 
Pretty boring ignition all around.

15-16,000lbs between my Travelette, my trailer, my heavy trail Scout, 
and a spare 392 in the bed.

90+degF ambient temp, with "hot air intake" stock filter assembly under 
the hood.

On the way to RMIHR, I ran 85 octane fuel the entire way.  ~4k feet and 
higher elevation (not sure what the low point was).  Even after running 
for several hours, engine temp approaching 230degF, climbing a big steep 
hill, with my foot to the floor (0" vacuum on the gauge).. NO PING.

I *am* near the limit, though.. on the return trip, outside of Grand 
Junction, Colorado, it pinged twice while pulling a hill.  If I left it 
a little vacuum, it was fine.. and only in one particular spot did I 
have a problem.

Dunno if it was bad gas, the right amount of air, or what.. but I 
couldn't reproduce it 10 minutes later, so I'm not going to touch the 
timing.

This is @406cid, polished chamber, ported n' polished heads (exhaust and 
chamber only), Isky 256/262 grind (12" of vacuum at idle.. <VBG>), 
headers, 1405 carb w/ LPG intake gaskets, dual Turbos.

I'll also add that with 4.30 gears and 235/85-16s, I need to start up 
hills at 65+ to really pull 'em.  If I can get the tach to edge past 
3000rpm (65) at the bottom, I can *accelerate* up most hills (again, 
15-16k!).  I can't seem to just *hold* 65mph though.

With the T-35, I can pull 55-60mph in 4th at redline, of course.

If I wanted to haul at 65mph, I think I would gear down from my current 
4.30 R&P and get a 4.88 third member, and if necessary, step up a little 
in tire size to get to 3500rpm@65mph.

Instead, I think I'll keep running 75mph.

Preliminary mileage figures fluctuate from 5mpg to 9mpg..

-Tom Mandera, Helena MT
http://www.tmcom.com/~tsm1/scout
'74 200 Travelette - 392/T35/RA-15/4.30/235-85-16  Long-box