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Home 1998 Editions April, 1998

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Chrysler Corp. hasn’t built a rear wheel drive,V8-powered car (with the exception of the Viper) since the turnof the decade. And the cars that harbored V8s beneath their hoodsduring the late 1980s were about as appealing to performance enthusiastsas the front-wheel driven vehicles that replaced them.

In spite of that fact, there’s a surprisinglystrong demand for high performance Chrysler small block engines.Certainly, much of that demand is fueled by truck owners as the318- and 360 cid variants of Chrysler’s "LA" small blockhave been offered in both Ram and Dakota models for several years.

The "LA" family of small blocks emergedin 1964 when a 273 cid model was introduced. In 1967, Chryslerstepped up the small block’s performance potential with a 318cid model. And this particular engine over the years has generatedmuch confusion.

Chrysler’s original 318 engine, which was producedbetween 1957 and 1966, bore the "A" series family designationand was a larger displacement version of the 277 and 301 enginesintroduced in 1956. Very few parts are interchangeable betweenthe old "A" engines and the newer "LA" powerplants.Few performance parts are available for the old "A"series engines, primarily because nobody cares.

Like its ancestor, the "LA" enginedidn’t have much of a performance orientation until 1968 whendisplacement reached 340 cubic inches. In 1971, a 360 cid versionwas introduced, but initially it was simply a torque generatorfor Chrysler’s larger vehicles.

Blocks

Chrysler "LA" blocks are easy todistinguish from one another because displacement is clearly notedon most castings. Although all blocks are virtually identicalin physical appearance, 340 and 360 cid versions accept a differentleft-side motor mount than their 273 and 318 cid counterparts.All production "LA" blocks have two-bolt main bearingcaps, and although kits are available to convert these blocksto a four-bolt main configuration, they should be avoided. Theproduction blocks don’t really have enough material in the webareas to comfortably handle the added bolts.

If four-bolt mains are required, so is additionalblock strength. The only way to get both is with a Mopar Performance"X" race block (p/n P4120637). It’s also possible toadd four-bolt mains to an old Trans/Am block or a p/n P3870873race block.

All 273-360 production blocks were cast usinga thinwall process and, as such, a .030" overbore shouldbe considered a maximum. Some older blocks (cast before 1976)may tolerate up to a .060" overbore, however, whenever youplan to machine the cylinders of an "LA" engine morethan .030" over size, it’s advisable to sonic check the cylindersto ensure that core shift isn’t excessive. You may find, especiallywith later blocks, that .020" is the maximum safe over bore.

With a small block Chrysler, standard highperformance block preparation is no different than with any otherengine. Typically, machining includes removal of casting flashfrom the lifter valley area, enlarging of the oil return holesin the valley, cleaning all critical threaded holes with a tap,machining of the deck surfaces to assure they’re square and flat,and chamfering the head bolt holes after decking the block.

As a general rule, high performance small blocksshould be machined to yield a zero deck clearance between thepiston top (the flat portion, not the dome) and the block whenthe former is at TDC. A "zero deck" improves power outputand also makes the engine less likely to detonate. However, many"LA" cylinder heads have completely round combustionchambers, so the only way to achieve a "zero deck" isto have the pistons actually stick out of the block .018"to .020" at TDC.

Regardless of the desired deck clearance, takethe time required to assure proper machining of the deck surfaces.Small block Chrysler engines have only two rows of head boltsso the block and head mating surfaces must be absolutely flatif the head gasket is to enjoy a long and successful life. Suggestedtorque for head bolts on high performance Mopar small blocks is100 lbs./ft., so thread integrity and head bolt quality are critical.

Without question, honing the cylinders withtorque plates in position is an essential part of machining anyhigh performance engine. Garry Grimes of Grimes Automotive Machine,Alpharetta, GA, notes that cylinder walls can move as much as.004" when the head bolts are tightened so use oftorque plates during honing is absolutely essential if optimalring seal is to be achieved. Grimes typically hones at least .004"to .005" after boring to assure optimum cylinder wall finish.Align honing is another operation that’s standard procedure whenmachining a block for high performance usage.

Crankshafts

All "LA" engines produced prior to1973 were equipped with forged steel crankshafts. Since 273, 318and 340 small blocks all have the same stroke and main journaldiameter, crankshafts are interchangeable between these engines.Production 360 engines, however, were never blessed with a forgedcrank and since they have 2.81" diameter journals, ratherthan the 2.50" journals found in smaller displacement "LA"blocks, retrofitting isn’t an option.

When interchanging crankshafts, keep in mindthat the balance factor will vary considerably depending on theconnecting rods and pistons used in the original configuration.The addition or removal of an excessive amount of material maybe required when using a crank in an engine with a bore size differentfrom the one to which the crank was originally mated. Therefore,the most efficient approach is to use a crankshaft that was originallyinstalled in an engine of the same displacement as the one beingrebuilt.

When preparing a crankshaft for use in a highperformance engine, it’s best to "buy a little insurance"by taking the extra time required to radius the oil holes, polishthe journals and add a generous fillet radius where the journalsmeet the flank. Obviously, it will be necessary to chamfer thebearings so they’re compatible with the new radii.

The crankshaft numbers of interest are: 2843868,1968-’72, 340; 2843883, 318 truck; and 3751162, 340 cast iron.Although a forged crankshaft is obviously stronger than one manufacturedof cast iron, crankshaft strength is rarely a problem in a highperformance street engine. However, when selecting components,be aware that cast iron 340 crankshafts are externally balanced,while "LA" forged cranks are internally balanced.

Consequently, the vibration damper and flywheelor torque converter designed for a cast crank must not be installedon a forged crank, and vice versa. The vibration dampers installedon 360 crankshafts are unique and are not suitable for other assemblies.

Another caveat regarding "LA" vibrationdampers is that 1972 and later dampers (p/n 3614369) have a symmetricalpulley bolt pattern while the 1971 and earlier dampers (p/n 2951673)have a non-symmetrical pattern. The 340 cast crank requires Chryslerdamper p/n 3751169; 360 engines require either a 3512972 or 3751808damper. Another option is to install a viscous vibration damper.Fluidampr p/n 71420 fits all internally balanced 318, 340 and360 engines.

Bearings

Don’t scrimp on either the rod or main bearings.Install top quality parts. Main bearings with a grooved upperhalf and full width lower half are recommended by most high performanceMopar specialists. When trial fitting the upper halves, make surethat the oil hole in the bearing is aligned with and is as largeas the oil supply hole in the bearing saddle.

If it’s necessary to drill a larger hole inthe bearing, be sure to deburr it. Bearing clearances are typically.002" to .0025"; tighter clearances – .0015" to.0018" are certainly permissible, however, when the acceleratorpedal is beneath the foot of an uneducated driver, tight clearancescan prove detrimental to the life of the bearings; engine oilmust be thoroughly warmed (above 200° F) before escapadesare made into the land of full-throttle operation.

Oiling system

In years past, high pressure and high volumeoil pumps have been standard issue for high performance engines.But metallurgy and lubricating technology have come a long way,eliminating the need for extremely wide bearing clearances. Tighterclearances eliminate the need to flood an engine with oil to compensatefor internal leakage.

If a small block Chrysler is assembled properly,and all recommended clearances maintained, a standard oil pumpwill provide more than adequate pressure and volume. In fact,high volume pumps can be a liability if crankcase capacity isn’tadequate because they can literally suck the oil pan dry – resultingin oil starvation – while filling the upper part of the enginewith oil.

The old guideline of 10 psi for every 1,000rpm is entirely applicable to Chrysler small blocks. Chrysler’soil pump blueprinting specifications call for clearance betweenthe rotor and oil pump body to be less than .014" and tipclearance between the inner and outer rotors of less than .010".A clearance of .004" is specified between the pump face androtors. Standard pumps properly prepared should provide the requiredamount of pressure in engines that won’t operate above 6,000 rpmfor extended periods.

If oil pressure isn’t adequate, a Mopar Performancehigh pressure oil relief spring (p/n P3690944) can be substituted.Additional volume can be obtained by installing a long rotor kit(p/n P3690944).

If at all possible, install a windage tray.Chrysler offers p/n 2531945 for 273, 318 and 340 engines and p/n3577794 for 360 engines. In both cases, a hardware installationkit (p/n P3690939) is required.

Keep in mind that oil pan selection for a Chryslersmall block engine is dependent upon the chassis into which theengine will be installed. Vans require a front sump pan, passengercars call for the sump to be in the middle, and trucks requirea pan with a rear sump.

Connecting rods

Chrysler small block connecting rods are essentiallyall the same. And, Mopar connecting rods do have a good bit ofintegrity. All are forged, but the 340 rods (p/n 2899495) arebigger and stronger than their 273/318 counterparts (p/n 2406785).Both part numbers have full-floating wrist pins. The 360 four-barrelrod (p/n 3751015) is also a heavy duty forging, but has a pressedpin. All small block rods have a 6.123" center-to-centerlength, but 1974 and later 318 and 360 rods are of the pressedpin design.

Pistons

This is one area in which attention to detailis critical. The compression distance of replacement small blockChrysler pistons can vary from 1.740" to 1.840". Thatbeing the case, some pistons will yield a deck clearance of .082"while others will stick out .018" above the block’s decksurface. Be sure that the pistons selected are compatible withthe cylinder heads and will provide the desired amount of deckclearance.

Also note that 4.040" is the standardbore diameter for a 340 engine while a 360 has bores that measure4.000". Consequently, if a 360 is bored .040" oversize,340 pistons would fit the bores, but the compression height wouldbe wrong because a 340 has a 3.31" stroke, a 360′s measures3.58".

To avoid problems, verify piston compressiondistance as early in the building process as possible. It willalso be necessary to determine combustion chamber volume so pistonscan be selected to provide the desired compression ratio. Mostperformance pistons are of the flat top persuasion, with eithertwo valve reliefs, a trough, or a dish.

With the large combustion chambers found inmany late model heads, compression ratio will be well below 9.0:1.Depending on camshaft duration, most street performance enginesshould have a compression ratio between 9.0:1 and 9.5:1. Pistonsshould be fit according to the manufacturer’s recommendations.Most forged pistons require .004" to .005" piston-to-cylinderwall clearances, although some "street type" varietiesare designed for .0015" to .002" clearance.

Piston rings

Standard fare is a Speed-Pro® plasma molytop ring, cast iron second, and low tension oil ring. As far ascylinder wall finish, simply follow the recommendation of thering manufacturer. The love affair many race engine builders hadwith exotic stones, mirror finishes and other "tricks"evaporated years ago.

Ring width selection is determined by the pistonsand a 5/64", 5/64", 3/16" combination is generallypreferred for street engines; 1/16", 1/16", 3/16"is commonly used in oval track, road race and bracket-style dragrace engines. As usual, there’s a trade-off. Wider rings offerbetter durability, but they’re heavier, so they don’t seal aswell at high rpms (above 6500).

High performance engines tend to build moreheat than their grunt-and-groan counterparts, so ring end gapis more critical. Common practice is to use "file-to-fit"rings (.005" larger in diameter than the bore) so that endgap can be precisely set. Minimum end gap dimensions are .016"for top rings and .012" for second rings, but end gap istypically much wider when hypereutectic pistons are used.

The hypereutectic material doesn’t transferheat through the piston as rapidly as a standard cast or forgedpiston. The advantage is that heat trapped above the piston canbe converted to power; heat transferred through the piston islost. The additional heat retained in the ring area requires endgaps of .022" to .026" for the top ring. This informationcan be found in the piston installation instructions that rebuilders/techniciansoften toss in the trash without reading.

Be sure to use a proper ring expander duringinstallation and don’t wind the rings onto the pistons. For bestring seal, make sure that vertical clearance between each ringand its groove is tight. Ring grooves for 5/64" rings shouldmeasure .0785" while grooves for 1/16" rings shouldbe .0635" tall. In both instances, tolerances are +.0005",-.0000".

Camshaft

Every gearhead loves the sound of an enginethat harbors a long duration camshaft. Unfortunately, the soundof performance doesn’t guarantee that an engine will produce thedesired amount of power. Consequently, the safest bet for an enginerebuilder is to be conservative with camshaft duration, makingsure it’s compatible with static compression ratio.

High compression and short cam duration leadto detonation. Low compression and long cam duration zaps cylinderpressure, which in turn zaps power output. The idea is to selectcomplimentary components that result in an engine that pops thegauge to 165-175 psi in a cranking compression test – that’s thetarget to assure compatibility with pump gas. (Competition enginesthat are fueled by high octane racing gas should register about220 psi).

Compared to a stock camshaft, a high performancegrind typically increases horsepower by holding the valves openlonger and raising them higher. There’s no mystery there, butthe latest computer-aided designs offer significant power increaseswithout having to rely on excessively long duration which resultsin a rough idle.

Cam lobes designed within the past few yearsopen and close valves at higher velocities so the valves reachfull lift sooner, stay there longer and close quicker. That translatesinto increased air flow potential which leads to more power, allother things being equal. However, current camshaft designs deliverthis increased power while still maintaining strong low speedtorque, good drivability and acceptable idle quality.

What about mechanical lifters? Unless you’rebuilding a race engine – avoid them. They require extra maintenanceand also increase maximum potential engine speed. Hydraulic liftersare hard pressed to deliver much more than 6500 rpm and that safetyvalve will serve you well – especially with customers having moremoney than sense.

Cylinder heads

Selecting cylinder heads for a high performanceChrysler small block is relatively easy. The best choice for 340and 360 high performance engines is a large port casting with2.02" intake and 1.60" exhaust valves. Heads fittingthis description were originally installed on 1968-’71 340 engines(c/n 2531894).

In 1972, intake valve diameter was decreasedto 1.88", but port size remained virtually unchanged. Largeport heads with the smaller intake valve (c/n 3671587) are suitablefor 318 engines, while 273 engines are well served with smallport castings having 1.75" intake and 1.50" exhaustvalves (c/n 2465315, 2536178, 2658920 or 2843675).

For serious street performance and racing applications,the W2 head (p/n P3870812 for the standard W2, p/n P4120043 forthe "econo" version) is the obvious choice. These headswere never installed on a production engine, so the chance offinding a pair through normal rebuilder channels is pretty slim.However, they are still available from Mopar Performance and canfrequently be found at Chrysler-oriented swap meets.

Regardless of the castings used, preparationshould include a multi-angle valve job (45°, 60° and70° cuts below the valve and a 30° top cut) which isalso part of the program. Under no circumstances should you sinkthe valves. If the seats are worn excessively, install new ones(which is often necessary with older castings not originally designedfor use with unleaded fuels) or oversized valves, which improveperformance in two ways.

A larger diameter not only increases air flowpotential, it also moves the valves higher in the chamber, therebyunshrouding them. As a general rule, best performance is achievedwhen the distance from the valve seat to the short turn radiusis at least .100". Installation of oversized valves makesit easier to achieve this dimension.

To make the most of each port’s flow potential,clean up the valve bowl area. The goal here is to smooth and blendthe areas where the machined and as-cast surfaces meet, and minimizeany obvious flow restrictions. Extensive porting and polishingare not required for street performance engines, though most customerswill expect the port openings to be matched to the gasket size.Except in extreme cases, the effect on performance is marginal.However, the effect on a buyer’s perception of power potentialis significant.

Installation of valve springs is part of anycylinder head reconditioning, but spring usage is dictated bythe camshaft. Most of the milder performance cams require nothingmore than a decent quality stock diameter valve spring – providedthat spring offers a minimum of 100 lbs. of seat pressure at aninstalled height of 1.700". More radical camshafts typicallyrequire stiffer dual valve springs which require spring seat machiningbecause of their larger OD (1.430" versus 1.250"). Theheads should also be fitted with premium quality valves.

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Dave Emanuel

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