Stroked and Poked


Previously, you had answered a question on smallblock stokers and mentioned
running a 4.080˝ bore / 3.79˝ stroke engine for a long time. I have been thinking about
this combination as a replacement for the 318 in my ’72 Satellite Sebring Plus even
before I read that. I have a 1968 340 core available that needs bored out at least
+0.040 to clean up. I like the 3.79˝ better for crank stiffness, especially if I go with
the 340 block vs. a 360. Also, that stroke gives some room to run a rod in 6.30˝
range and still have some amount of skirt and ring pack stability on a short piston
and rod ratio getting closer to stock. Two questions: 1. Do you have any writing on
the 3.79˝ stroke engine you ran? 2. Have you ever heard of anyone running big
block rods in a small block and is it feasible? B block 6.358˝ rods would be a good
length with the 3.79˝ stroke and seem very stout and easy to find. The big problems
I see are needing the crank custom ground to the big block rod journal from
the supplier and narrowing the rods to get proper side clearance.

That engine (which I think was actually 4.060˝ bore) was run for many years
in our One Lap of America ’69 Valiant (Green Brick). The secret to durability and
longevity: we used a Mopar Performance “X” block, 4-bolt mains, thicker decks
and webs, etc. Generally, I do not like the idea of running even that long of a stroke
in a small-main (273/318/340) LA block. The larger mains in a 360 block not only
increase the block strength, they impart greater strength to the crankshaft (greater
overlap). That’s how a 4˝ cast iron crank is able to live.
I won’t even address the rod issue. With non-fatigued new forged rods, better
alloy and fasteners, costing little (if any) more that reworked stock rods, wake
up and smell the coffee! I like OEM parts more than most, but we’re talking 40-50
year old stuff here. The 408 / 360 combo is nothing new, and while it was, admittedly, never subjected
to “Chelsea Proving Grounds” (and dyno) long-term durability testing, it has
been built so many times, and run so many user-miles, that any inherent problem
would have surely been uncovered by now. A 408, at 0.030˝ O/S 360 bore diameter,
will also have thicker walls (a bit) than yours. And 360 LA blocks can be had that
are less than 20 years old and, in your 3880 lb. B-body, would be exactly what
the doctor ordered, and you’ll be way ahead financially. Leave that 340 block to
the numbers-matching guys. They’ll pay nosebleed prices for it. Don’t sweat the rod ratio or skirt length
tales. Take apart a 3G Hemi and tell me what you see.

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