continued article by Richard Ehrenberg:
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
icher 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.
Hotrodding
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 houw 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 hotrodding
techniques, and then some. In fact, with such a bountiful set of basic
ingredients, hotrodding this engine seems a natural.
-by Richard Ehrenberg.
=================
end of part three
This archive was generated by hypermail 2b29 : Fri Jun 20 2003 - 12:12:35 EDT