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Chrysler's New Cammer

Tech analysis of Mother's first all new production V8 in 41 years.
4.7L OHC 16 Valve V-8     by Richard Ehrenberg

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NOTE: This entire work is copyright 1999 by Richard Ehrenberg and Harris Publications, Inc., New York, NY. Used by permission which may be revoked at any time. Retransmission, copying, posting elsewhere, distributing printed copies, and all similar activities are prohibited. Protected by US copyright laws and international copyright treaties. Violations will be prosecuted aggressively."

Subject:    DiRT: 4.7 Cammer Tech Article
Date:        Tue, 9 Feb 1999 15:36:09 -0500
From:       hl1@acpub.duke.edu (Henry LaViers)
To:           dirt mailing list

The following is an article about the new 4.7L single overhead cam V8 written by Richard Ehrenberg who writes the technical advice column for Mopar Action magazine. These excerpts are from Volume 10 Number 3 (April 1999).

Notice the references to 'after all it's just a truck engine' and the emissions comments.

The good news is that it does not have a rubber timing belt.

And please think of this as a 'teaser' so that you will consider going out and buying the magazine to get the great illustrations.

-Hank
==============================

 

Specifications 1999 Power Tech 287 cu. in (4.7L) V8

  • Type 90 deg. V-8, 16 Valve
  • Country of Origin: USA
  • Hp, SAE Net: 235hp @4800 rpm
  • Torque SAE Net: 295 ft-lbs @3200 rpm
  • Fuel Required: 87 octane unleaded gasoline
  • Bore x stroke: 3.66" x 3.40"
  • Compression Ratio: 9.5:1
  • Weight (complete): 438 lb
  • Valve Actuation: Chain driven overhead cams
  • Block Material: Cast Iron
  • Block Design: Removable bedplate
  • Head Material: Cast Aluminum
  • Intake Manifold: Glass filled nylon, single plenum, ram's horn runners
  • Fuel Supply: head mounted multipoint injectors
  • Crankshaft: Cast iron, cross drilled, radiused, fully counterbalanced, 5 main bearings
  • Connecting Rods: Powdered metal, cracked caps
  • Bore/Stroke ratio: 1.08
  • Rod/Stroke Ratio: 1.80

 

Dateline: Highland Park, Michigan, fall 1957.

The 1958 Dodge and Plymouth are introduced with an all new, modern B-engine, the 350 and 361 cubic inch V8 option - the very engine we've seen grow to 400 cubes, and, in its tall-deck variety, the famous 440.  Although spawning the all-conquering 426 Hemi, this series lived only through 1978, at which time it was an innocent victim of corporate near-bankruptcy, emissions, and fuel economy mandates.  But who would'a thunk that it would take another 41 years - 1999 model year - before Chrysler would introduce another all new V8 engine? But it's here - now.  Since the new Power Tech 287 inch V8 (4.7L for you metric fans) is designed to replace, initially, the famous 318 (5.2L) Magnum mill, which, itself, was an outgrowth of the first smallblock Chrysler engine in 1955, we'll begin with a brief history lesson.

     The "A" engine, introduced in 1955, was Chrysler's first attempt at an 'economy' V8 engine.  The Hemi, Chrysler's first V8, when introduced in 1951 at 331 inches, was anything but economical to manufacture: Complex head castings, four rocker shafts, etc.  So the A engine-ers tried to keep some of the best features of the Hemi, but with pared down costs.  A single rocker shaft was mounted on each head, with opposed valves operated via splayed pushrods.  While this engine was never really a killer performance-wise, it stood the test of time, and was produced by the zillions through 1967.  Most common was the 318 inch variety.

     In 1964.5, a new, thinwall-block version was added to the A-stable. With a 273 inch displacement, it was designated the LA engine.  Modern wedge-chamber heads would set the standard for decades to come.  Over the next 7 years, variants would include the 318 and 340 inch displacements, with a larger main bearing 360 joining the rostrum last (1971).  These engines would continue, with incremental changes and updates (single port EFI, roller cams) through 1992-1993, when the now common Magnum multiport fuel injected update came on-stream.

     The Magnums, though sharing very few actual components with its predecessors, was still an LA engine, through and through.  All key dimensions: Bore, bore centers, bearing sizes, can-to-crank, etc., remained just as they were in 1955 !

     Which brings us to 1999.  The new 287 is just that, new, sharing almost nothing but a heritage with the ol'reliables.  For starters, it's the first true production Mopar V8 mill to incorporate aluminum cylinder heads ( okay, we know about the 1965 A-990 Hemi ) a plastic intake manifold, and magnesium valve covers.  Nothing is re-hashed here, and the combustion chambers are almost hemispherical !

     And, although it might take a year or two, we'll bet that variants of this powerplant - the "C" engine? - with more or less cylinders, and varying internal dimensions will replace virtually all RWD gasoline powerplants now in the Chrysler stable.  In other words, this is a real milestone.  So let's take a detailed tour of what's what, what fits what, and start some good rumors about where DC will take this engine in the future.  We'll begin at the lower extremities.

The Bottom End

     Virtually all dimensions of the cast-iron block are new.  The bore spacing is reduced from the 1955-1998 small block's 4.46 to 4.09" - this an indicator of how large the new engine eventually could (or could not) be enlarged to.  Basic bore size is 3.66," larger yes, than a 273 (by a mere 0.030) but smaller than all the other A-engines - the 318, even going back to the 1950s, was always 3.9."  Why ?  Small bores are easier to clean up for emissions.  Speaking of bores, the roundness is held to a maximum of 0.00015", and taper to 0.0006" - virtually race engine specs.

     Deck height is 9.09," compared to 9.60 for the ol'LA mill.  As a even more profound indicator of jest how new the new design really is, even the offset of the LH cylinder bank is reduced.

 
Like the current LA-based V10, the 287 doesn't use individual main-bearing caps.  Instead, what Chrysler calls a 'bedplate' (girdle to us old hotrodders) clamps all five mains at once, adding rigidity while reducing noise and vibration.  The bedplate is high-tech even to the material - compacted graphite iron. 
It is sealed to the block with the old standby: RTV silicone sealer.  Incidentally, this bedplate is such a beefy piece that disassembly is almost like 'splitting the cases' on a motorcycle engine.

The crankshaft is nodular cast iron, hardened and microfinished.  A one piece rear main seal, similar to the 2.2L design, seals to the outside of the 100mm o.d. rear flange, which is an 8 bolt, one-offset pattern, in Chrysler performance tradition.  Main journals are 2.5" diameter, identical to the 318/340 (the 360 is 2.81"), and are crossdrilled.  Rod journals are 2.0", 1/8" smaller than the 318's 2.125.  All journals have rolled fillets, a significant step taken, in the best racing engines, to prevent stress cracks from forming.  Balance is better than 18 gm/cm, and torsional vibrations are looked after by a modern 3 spoke-style snout dampener, with most of the weight placed where it will do the most good - at the outer diameter.

The stroke is 3.405", a shade longer than the 273-340 was at 3.31, but shorter than the 360's 3.58.  Still we'd call it a 'short stroke' engine. Looking briefly at the block, there is room for some stroke increase. Having the cam out of the way helps a lot.

Carrying on a performance small-block tradition begun with the 1968 340, all bearings are bi-metal Federal Mogul aluminum alloy.  As in all production small blocks, only the upper half of the mains are grooved. Unlike the previous smallblock, however, thrust isn't taken by a lip on #3 main.  Instead, two (front and rear) separate 180-degree thrust bearing/washers float on the top half of the usual (for Mopar) #3 main journal.

Connecting rods.  Yes !  The long-rod Mopar tradition continues.  The 6.12" length, same as all LA engines have always been, puts rod/stroke ratio at a very favorable 1.80, better than the current 360, and only a shade worse than the 273-340.

 
But the traditional forged steel rod is gone.  Now you'll find powder-forged metal cracked rods.  In this process, first used by Chrysler in the 2.0L SOHC Neon engine, the rods are produced and machined in one piece.  Then the caps are literally cracked off, guillotined if you will, resulting in an absolutely perfect mating surface that almost lock together, preventing cap walk.  Fasteners are hardened M9 capscrews threaded directly into the rod, no nuts are used. 
Rod weight is 556 grams, compared to 726 to 758 grams for various production LA-engine rods.  0.945" wrist pins, weighing in at 143 grams, are press-fit in the rods.

Compression ratio is "blueprint" (and advertised) at 9.5:1, and typically measures 9.0:1. { The Grand Cherokee DC website lists CR as 9.3:1 } Regular (87) fuel is recommended.  But the design allows for high-compression domed pistons in the future.

Pistons are cast aluminum, have moly coated skirts for break-in scuff resistance, and weigh 366 grams.  They are fitted at 0.0008-0.0020" skirt clearance - rather snug but nothing unusual for a street engine.  The usual 3-groove ring pack is used (.062/.062/.120") but in addition to the common plasma-moly-filled top rings, the second ring is chrome.  Oil rings are chrome as well, with a stainless expander.  Bucking the current trend, the oil ring tension is rather high (12 lbs) allowing good oil control even in high-mileage engines.  In fact, the spec for the 95th percentile customer is 150,000 mile useful life.

In the never ending quest to reduce emissions, the distance from the top ring groove to the top of the piston has been reduced to only 1/8th of an inch, making these areas susceptible to excess wear and heat.  To combat this, the top ring land, and the area from the land to the head, are hard anodized.

No oversized pistons are available, and the replacement pistons/rods are supplied only as an assembly.  Can you say aftermarket?

 
The oiling system isn't radical, using a clever design first seen on the AMC V8s: the georotor-type pump is mounted in the timing cover, and is driven off the crank snout.  Direct drive, unlike the current LA engine, which, if you think about it, is a nightmare.  The oil pump drive torque comes off the crank nose, through the chain, to the cam, back through the full length of the cam, through a bevel gearset to the intermediate shaft, and then through a hexagonal drive to the pump itself.  Whew !  Can you say, simplified ?

The new, block mounted pump has a 75 psi relief valve, and a displacement of approx 1 cubic inch per revolution.  The oil pan is stamped steel, includes a windage tray (integral with the pan gasket) and has a capacity of 5 quarts plus one in the filter.  Pump clearances are designed for the recommended 5W30 oil.

Topside - Heads

They are Chrysler's first real production light-alloy V8 cylinder heads
Semi-permanent mold aluminum castings, the heads break no new ground but are nonetheless state-of-the-art.  Head bolts are 11mm, but the meat is there for a future upgrade to a performance version 12mm.  The head bolt pattern is the same for each cylinder (and almost perfectly square at 4.00 x 4.10"), and retains the traditional LA 10 bolt per head arrangement.  A super quality 3 layer laminated stainless steel gasket seals the deal.  The heads are 'handed' - ie. not interchangeable side to side, mostly because the ports are in a different order left to right.

 
The intake valves are 1.89", and the exhausts are 1.46," in keeping with the latest Detroit theories regarding Intake:Exhaust valve diameter ratio. With the intake splayed at 13 degrees, the 64cc combustion chamber is approximately hemispherical in shape.

  Typical Mopar 3-groove, flash-chromed stems, hardened tips, and a length of 4.45" gives you an idea of the valve package - nothing radical, but a generous intake size for the displacement.  Guides are press-in, and the stem diameter is approximately 9/32" - even smaller than the 5/16" used on Hemis and Magnum V8s.  This is obviously to improve flow and reduce friction.  Springs are moderate, but adequate, given the 6,000 RPM fuel shutoff point.  But the valve actuation - that is something else again.  Gone are the pushrods - forever.

 
A head mounted camshaft on each cylinder head operates the valves through a set of needle bearing roller rocker arms, with opposite-end hydraulic lash adjusters acting as the fulcrum, a system not unfamiliar to anyone who's ever played with an '88 or newer Trenton I-4 (2.2 or 2.5L).  But looky here, the Intake and Exhaust rockers are opposite each other.  Yup, it's almost a Hemi.

The cams are each driven by a separate chain, each of which are driven off an idler, in the approximate location of the ol'LA's cam sprocket.  This idler sprocket, in turn, is driven from the crank in typical pushrod practice timing set fashion.  The camshafts themselves are radical - although not in lift or duration.  These are truck engines, after all: 0.443" lift on the intake, and 0.429" on the exhaust, duration is 244 degrees intake, 254 on the exhaust, partially compensating for the smallish exhaust valves.  Overlap is only 18 degrees.  This is an emissions, and torquer motor, remember.

What makes the cams radical isn't the timing, but the construction.  They are hollow steel tubes with the individual lobes, of powdered metal, sinter-bonded in place.  In fact, the cams, being hollow, are used to bring oil to the intake lobes, which have oiling holes.  Cam (valve) covers are cast magnesium.

The ports are 1.86 square inches at the port face, and the injectors are mounted to the port in the head, not the intake manifold, which as we shall see, is made of polymer.

Speaking of intakes, this is another cool deal - literally.  Following in the footsteps of 'little cousin 2.0 SOHC,' the manifold is a one piece glass filled nylon thingie.  With a lengthwise plenum and 8 cross-over ram-type ports, it's quite a shock, especially if you are used to LD-340s and M-1s.  Runner length (in manifold only) is 20 inches, and there's quite a bit of port length in the heads, so the mill clearly isn't designed for 8,500 RPM passes.  But the all-plastic construction should go a long way toward keeping charge-air temperatures down, aiding HP production.

Up top, a single bore, side draft throttle body measures 2.56" diameter. If that sounds small, remember that a medium sized Holley 4-barrel has typically bores of 1.625."  Doing the math, that computes to 8.3 square inches for the carb, and 5.1 square inches for the EFI throttle body.  But remember that the carb has to pass the air around not only the throttle blades, but through the much smaller - and more restrictive - venturis. We're willing to bet that this throttle assembly passes about as much air as a 600 CFM carburetor !  Not bad for a 287-inch powerplant, eh ?

Exhaust manifolds appear to be logs, especially in the initial Jeep version (We expect the Dodge truck ones to be better.)  But they are, in reality, individually ported, and not nearly as bad as they look.  Heat shield over them is super high-tech - aluminum core with stainless on each side.

Electronics

There are two interesting electronics-related details worth noting.  First, this engine has coil-on-plug ignition.  No plug wires, a separate ignition coil mounts to each plug.  This something all us guys with headers and toasted plug wires can really appreciate.

Even wilder is the absence of a throttle cable - it's fly by wire, dudes. All you're doing when you mash the 'gas' is sending a signal to the computer, which will, hopefully, respond faster than "All ahead full....aye, aye, captain."

The Future

Will the 287 replace the 318 in Dodge trucks, SUV's and vans?  Definitely, by the fall of '99 for sure.  But here's where our engineering analysis ends and sheer speculation begins, guys.  There's no secret mad of the fact that a V6 version will be available soon.  Will it replace the LA-based V6? Absolutely.  Will it replace the current Jeep I6? Probably.  Will the 287 power the Prowler?  Sure, makes sense to us.  But will there be larger versions built to replace the 360, and the 488 inch V10 in the trucks and Viper? Hmm.  Surely logical, but with the smallish bore spacing, don't look for this engine in V8 form to go much over 330 inches.  Would say, a 325 incher be able to take over from the 360?  Why the heck not?  The 287 makes virtually the same torque and a tad more HP as the 318 Magnum (albeit at a greater RPM) so why couldn't a larger version do as well?

And a 400 inch V10, in a SOHC (forked rocker arm)/ 4 valve arrangement, could, with a bit more radical valve timing, a bit more squeeze (say 11.0:1) bigger ports, and shorter intake runners, should have no trouble making 475-500 HP.

Hot Rodding

Where will the aftermarket - and Mopar Performance - take the 287?  There's already a supercharger setup from Performance West, and available through any Jeep dealer.  But less radical upgrades would seem to be quite easy. Revised, premium fuel calibration - more spark advance, and a tad more fuel in the form of a computer chip flash would seem to be almost a must. There's room for larger valves, the Mopar machine shops are probably already plotting how they'll re-contour and flow the heads; headers are almost guaranteed, along with a less restrictive air intake setup, and Crane or Comp Cams will surely have cams for it.  In other words, we see no reason why this engine can't respond to all the usual hot rodding techniques, and then some.  In fact, with such a bountiful set of basic ingredients, hot rodding this engine seems a natural.

-by Richard Ehrenberg.


More From Henry LaViers

The disclosure about the new 4.7L V8 from Chrysler having only 1/8 of an inch from the top of the aluminum piston to the first ring got me a little interested in why this was done - and if we will be pulling up behind 4.7L V8's blowing blue smoke after a few years of wear.

An internet search led to this article, which says some interesting things. The whole article is much longer than this as I snipped much out to shorten.

Notice the surprising detail that better ring sealing is wanted - not to keep blowby from getting into the crankcase - but to keep crankcase vapors from reverse-blowbying into the cylinder and raising emissions during cold startups !

Of all the things that I read about the 4.7L, it is the aluminum pistons that worry me the most.

Hard anodizing (which means corroding the aluminum in a furnace under controlled conditions where the coat of corrosion will hopefully stick on like paint) may help but it only goes so far.

-Hank
======================

Pistons & Rings, Larry Carley, Automotive Rebuilder, Dec 1998

With each new generation of engines come changes that are designed to reduce emissions and extend durability. Key among these have been changes in piston and ring materials.

(snip)

Piston changes
 
One of the "tricks" that the OEMs are using to reduce hydrocarbon emissions is to position the top compression ring closer to the top of the piston. This reduces the volume of the dead space between the piston and cylinder wall above the top ring that traps unburned fuel and contributes to incomplete combustion.

But moving the ring up places it closer to the combustion chamber and exposes it to higher operating temperatures. Consequently, the rings need to be thinner to reduce inertia and made of tougher materials such as ductile iron or steel so they can withstand the heat. If ordinary gray cast iron rings are used in such an application, it would greatly increase the risk of ring breakage.

Another consequence of moving the top ring up is that it reduces the thickness of the piston land area above the ring, which also increases the risk of the piston cracking if the engine experiences detonation. For this reason, many of the newer engines today have hypereutectic pistons instead of ones made of ordinary cast aluminum

Hypereutectic alloys are much tougher than the alloys used in ordinary cast aluminum pistons. Hypereutectic pistons (which are also cast, not forged) have a very high silicon content ranging anywhere from 16-22%. The excess silicon forms little hard spots in the alloy, giving the piston improved wear and scuff resistance at high temperatures. However, the added hardness also makes the pistons much more brittle than ordinary cast pistons, which means hypereutectic pistons must be handled more carefully.

Another change is that many pistons are getting shorter as the OEMs reduce deck heights for shorter blocks and reduced hood clearance. To maintain torque output, longer rods are used which requires moving the wrist pin higher on the piston. This leaves less room for the rings, which means smaller rings must be used and crowded together more closely.

Reducing the thickness of the piston lands also increases the risk of breakage, so that's another reason for using hypereutectic pistons. The harder hypereutectic pistons experience less ring groove wear and do not need inserts as some pistons do to prevent land pound out.

Many of today's engines are also running much closer piston-to-cylinder wall clearances to reduce blowby emissions. Some clearances are .001" or less, which leaves little room for error or overheating. A tighter fit means there is less room for thermal expansion, which is yet another reason why the OEMs are using hypereutectic pistons in many of these engines.

Hypereutectic pistons expand less than ordinary cast aluminum alloys, and CNC machining of the piston profile allows piston-to-bore clearances to be reduced. This also eliminates the need for steel struts inside the piston to control thermal expansion, which reduces piston weight and complexity. Eliminating the steel struts inside the piston also eliminates a potential source of trouble that may, under certain circumstances, lead to piston cracking and failure.

(snip)

One of the drawbacks of having the top ring so close to the combustion chamber is that it reduces ring life. "If the distance is less than about. 0175" to .020", the top ring runs hotter and requires a larger gap," he said. "The top land is also weaker which makes it more vulnerable to cracking if there's detonation. So on some of our aftermarket pistons, we place the rings further down the piston in a more normal location to improve durability.

"We also destroke our aftermarket pistons .010" to .020" depending on the application to compensate for overboring and deck resurfacing. Destroking the piston maintains the stock compression ratio and reduces the risk of detonation."

Hayes said another thing rebuilders should be aware of is that not all hypereutectic pistons are the same. The composition of the alloy can vary, and the silicon must be the right size and evenly distributed in the aluminum matrix. If the alloy is not mixed right, the silicon can clump together forming hard spots in the piston. These hard spots concentrate stress and increase the risk of cracking.

(snip)

Forged pistons

Though forged pistons are used primarily in heavy-duty diesel truck applications and few OEM passenger car engines today, they remain a popular alternative for aftermarket performance and marine engine rebuilders.

The forging process eliminates porosity in the metal, which makes it denser and stronger. The type of alloy used in forged pistons is also up to 600% more ductile than that used in conventional and hypereutectic cast pistons. The result is a stronger piston that is well suited to racing and other equally punishing environments.

Forged pistons also run 18% to 20% cooler than cast pistons because the metal conducts heat away from the combustion chamber more quickly. This reduces the risk of detonation - but the trade-off is greater thermal expansion in the piston. Consequently, forged pistons require greater installed clearances which increases cold start noise and blowby.

Reducing blowby

Another change that may be coming in OEM ring designs is to use something to seal the gap in the top compression ring (some type of overlapping end gap). Though you might think the reason for doing this would be to reduce blowby from the combustion chamber into the crankcase, the real reason is to eliminate reverse blowby from the crankcase back into the combustion chamber.

When the piston goes down on the intake stroke, vacuum in the combustion chamber can pull oil and other vapors from the crankcase into the cylinder - especially during cold cranking and the first five to 10 minutes of engine operation. Sealing the gap in the top compression ring to prevent this from happening can lower start-up emissions 10% to 27%.   


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