Dodge RamCharger Central banner

LA Engines Part 2

22269 Views 0 Replies 1 Participant Last post by  GunPilot
273 = 3.625
318 = 3.91
340 = 4.04
360 = 4.00

273/318/340 = 3.31
360 = 3.58
These are the only strokes used in production LA engines. The 2.96 stroke crank from '70 was never used outside of Chrysler's T/A racing program. They are out there at swap meets (extremely rare, but I have seen one, 8 bolt flange) but I can't say whether or not the factory was selling them to the public, or someone just got his hands on a crank from one of the actual race cars. Found an article where it states Chrysler did in fact sell these cranks through their parts distribution chains, most likely only the racers were aware of this. As they are just extremely rare and expensive peices of Mopar history.

273/318/340 = 2.4995 - 2.5005
360 = 2.8095 - 2.8105

273/318/340/360 = 2.124 - 2.125

273/318/340/360 = 6.123

273/318 = 726 grams / 25.62 oz
340/360 = 758 grams / 26.75 oz

273/318/340/360 = .9842

273/318/340/360 = 2.99-3.00

273/318/340/360 = 154.6 grams / 5.45 oz

273 = Full floating '64-'69
318 = Full floating '67-'73
318 = Pressed pin '74-present
340 = Full floating '68-'73
360 = Pressed pin '71-present

273/318/340/360 = .935" +/-

The distance between the centerline of the piston pin and the top of the piston or crown. Not to include the dome or dish.

273/318/340 = 1.822
360 = 1.687

*These #s are "theoretical" to achieve 0.00 piston to deck clearance with a true blue print 9.6" crank centerline to deck height with the LA. Your actual build #s will be different. Bear in mind, there is a minimum piston to head clearance # specified for LAs. These numbers will not be cast in stone, as there is a high probability of casting irregularities, previously milled blocks and heads, swirl port chambers, etc., that will further reduce workable compression heights. But the minimum piston to head clearance, should be adhered to. As with any quality build, these #s (along with piston to valve clearance) should be verified, especially with high compression mills. There are examples of positive deck heights out there. The high compression 340s were "pop out" designs. Workable because of their open chamber designed heads. But these positive deck height pistons will not work with Swirl Port heads. As they have a "qusai" closed chamber design.

To figure out the piston compression height. Use this formula:
A + B - C - D - E = F
A = deck height
B = gasket compressed height
C = rod center to center length
D = 1/2 the crank throw
E = minimum head clearance (crucial when installing closed chambered heads, there is no room to play with as in regular open chamber heads)
F = maximum compression height. This # can exceed the deck height somewhat in high comp mills with open chambered heads. The early 340s had flat tops with O/C heads that exceeded their deck heights, but they still had a minimum piston to head clearance that had to be adhered to.

Example: 440 with closed chamber 915 castings. the 440 has a block deck height of 10.725.
(A)10.725 + the compressed gasket height, let's say (B) .039 = 10.764
Now 10.764 - the rod length of (C) 6.768 = 3.996
Now 3.996 - half the crank throw (D) 1.875 = 2.121
Now 2.121 - your minimum piston to head clearance, let's say (E).055 = (F) 2.066

This would be your maximum piston compression height assuming the block has not been decked below the factory blueprint. This would change the maximum P.C.H. (centerline of pin to crown of piston) not to include domes or dishes. Obviously, there is more room to play with when dealing with open chambered heads. Most engine builders use modeling clay to verify piston to head #s.


Too many people claim to have X compression, when they can not actually verify the number. It is impossible to dial in compression based on the piston makers claims of "10.0 compression with this model piston". There are way too many variables to approach engine building in this fashion. If this approach is taken, it will lead to an engine no better than the one you started with. May be more powerful than before, but we all start these build-up projects to correct Chrysler's short comings, not follow them. They had an excuse, they were building tons of them. While we are only building one.

273 = 569 grams / 20.08 oz 4V (2V=530/18.7 oz)
318 = 592 grams / 20.89 oz
340 = 719 grams / 25.38 oz
360 = 584 grams / 20.61 oz

CRANK MATERIALS (Casting #s to come)

All 273s had steel cranks and were internally balanced.

318s* Recently I found some info concerning forged 318 cranks. It stated '68 as the year of cast crank intro to the 318. I will do some hands on research and verify this. Even so, the 318 remained an internally balanced motor.

340s up till '72 had steel cranks and internal balance. '73s had cast cranks and a special damper for external balance.

360s from the beginning in '71 had cast cranks and external balance.

* 318s began their LA lives in '67. '66 and earlier 318s were A engines and are a totally different story.

All LAs had forged steel rods. 340/360 rods being the larger and stronger.

All 340s were made from the high nickel alloy. According to Larry Sheppard of Mopar Perfomance, some later blocks (early '70s 318s, and 360s) were of this material also, but I've never seen it documented. The search for the truth shall continue!
All blocks were 2 bolt mains. Rumor has it, that the T/A blocks were fitted from the factory with 4 bolters. This is not true. What Mopar did was cast the T/A blocks with heavier main webbings to more readily accept 4 bolt caps than the standard 340 blocks. But they were never fitted with 4 bolters from the factory. Another curiousity is the early 360s, up till '74. They have been reported by Chrysler to have been cast with 340 water jackets. This would give them the ability to accept a 4.1 bore, as the motors all have the same bore centers. I have seen this info in a few places. But I've never checked them myself, so I can't say yea or nay. Even if you could go this big, it would require costly pistons, or major modifications to '72/'73 340 .060 over pistons. So it may not be worth the trouble or cost for a few extra cubes.

All LAs share a common bell housing bolt pattern and starter location. Unfortunately, they do not share these patterns or locations with the Slant 6 or the B/RB.

All LA heads will interchange*. But there are 2 different port and valve sizes:
273/318s have small ports with the smaller 1.78/1.50 valves, as well as smaller combustion chambers.
340/360s have the big port heads with 1.88/1.60 valves** as well as larger combustion chambers.

* Big port heads will bolt up to the 273, but the 273 block will require notches for valve clearance. Which leads to shrouding of the valves.

** '68 - '71 340s used the big port (X) heads with 2.02/1.60 valves. '72 and '73 340s used the big port (J) heads with 1.88/1.60 valves.

The T/A heads are simply 360 big port "J" heads with relocated pushrod holes which allow more aggressive porting without hitting the pushrod hole. But they are not ported from the factory as some have claimed. They also require the special T/A rocker gear which is offset to meet the offset location of the pushrods. The port sizes and valves are the same as the '68 - '71 340 X heads.

The rocker gear for LAs, while they work ok, (no way to put this nicely) plain suck. they are not adjustable, flex is too great, and requires shimming the rocker shaft if too much deck or head surface is removed. And their true ratio is between 1.42 and 1.45 before the flexing starts. Another fix for the non-adjustability is the use of adjustable pushrods. While I've never used them, I know a few people who have. And they are not happy with them. Or one could get cut to fit pushrod kits. Using the T/A gear is out of the question unless you have T/A heads, because of the offsets cast into them. So the best gear available, besides aftermarket rollers, is the 273 adjustable rocker gear. They are rock solid and fully adjustable. And they are worth their weight in gold across the entire RPM band when compared to the stock stampers.

Contrary to popular belief, the LA spreadbore manifold is a really well designed piece. Unless of course you prefer the square bore carbs like Holleys. This manifold will flow well past a "stock" LA's head capabilities. They may not look as nice as the EB Performer, or be as light, but they will outflow the EB. The stock manifolds were designed for the big port 340 heads, unlike the Performer which was setup for the 318
See less See more
Not open for further replies.
1 - 1 of 1 Posts
1 - 1 of 1 Posts
Not open for further replies.