Text and Photography by
FM Staff
Overview
What does it take to make 400 horsepower out of a 302?
Sure, a supercharger or nitrous will do it, but we're
talking naturally aspirated. In this two-part series we
will show you that a well built 302, for no more money
than a standard performance rebuild, can make 400 or more
horsepower at the crank.
In Part One we will detail the short block preparation
and assembly, including our cam selection. In Part Two
we'll install the heads and intake, and figure out some
details for dropping the late model block into an early
Mustang project car. Finally we'll get it on the dyno
and to the track.
Our motor will be carburated and run a single plane intake,
which is going to push the power band pretty high in order
to make the ponies we are after.
Block and Crank
We started out with a high-mileage 1989 5.0L block out
of a daily driver
Seasoned 1989 5.0L "roller"
block. |
Mustang. We paid $50 for the
short block. You should have no problem getting your hands
on a used block for a similar price. We used the late-model
roller-block simply because they are abundant, and have
more power potential due to the roller cam.
Having 80-90 thousand miles on the engine we know the
iron is "seasoned" and ready to work hard. Most engine
builders will tell you that used cast iron blocks and
heads are much more reliable than brand new castings because
they have "settled" by going through many heat cycles.
Our objective was to make this a "budget" rebuild. Although
we didn't set out with a specific dollar limit, the goal
was to limit as much machine work and new parts expenses
as possible.
The cylinder walls still had a nice cross-hatch
pattern and showed no signs of damage, indicating
we may be able to get
by without boring the cylinders. We had the machine shop
New cam bearings and oil
galley plugs. |
measure the bores, and they
came up with 4.0015", at maximum taper. The piston had
another 0.001" of skirt wear. Assuming the honing process
would take the bore to 4.002", the block was still within
factory tolerances (4.000"- 4.002") They also hot tanked
the block to clean it out, and installed fresh cam bearings,
freeze and oil galley plugs. This cost us $100 even.
The crank was within factory tolerances for main and rod
journal diameters and runout. These are measurements which
you should let your machine shop check unless you have
the proper micrometer and dial indicators. We got away
with a simple crank polish and cleaning for $50.
Pistons and Rods
The initial plan was to use the stock pistons. In 1988
and 1989 Ford put forged TRW pistons in the 5.0L. However,
when we mocked up the heads and cam in order to check
piston to valve clearance we
Stock 1989
Ford (TRW) Forged piston. |
realized the larger intake valve
would interfere with stock piston. (See Measuring
Piston to Valve
Clearance in the Fundamentals section of the Tech
Department.) This put a literal bind in our plans to build
this motor dirt cheap. Our options were to have the pistons
"flycut" (a machining process which grinds larger and
deeper valve reliefs into the piston), or to buy new pistons.
In terms of cost, it was a wash. Flycutting requires the
pistons be removed from
the rods, so the labor cost would be $100, plus another
$80 for cutting larger reliefs.
Machining the piston makes it neccesary to rebalance the
motor; another $200 expense. The final result would
be a piston that is weaker,
and still has a limit as to how large a cam we can run.
On the other hand, a new set of aftermarket pistons, already
cut with large valve reliefs, cost about $200. We'd still
have to spend for balancing and getting the pistons pressed
on, but at least we'd have the peace of mind that the
pistons are good and strong and can accept larger cams
in the future.
We decided to go with the Keith Black 281 piston. It's
a lightweight flat-top piston which weighs 505 grams,
with a 102 gram pin, together this is over 100 grams lighter
than a stock piston. A lighter rotating mass translates
to less parasitic loss and thus more horsepower. Additionally
Jacks Engines in Oakland,CA
handled the machine shop duties. |
the KB pistons all come with
valve reliefs large enough to accept oversize valves as
large as 2.10" and 1.80" intake and exhaust
respectively.
Expect to pay between $150 and $200 for a complete balance
job. You will need to
bring to the shop your crank, rods, pistons, one set of
rings and rod bearings, as well as your harmonic balancer
and flywheel or flexplate. If your car is a manual transmission,
bring in your clutch pressure plate. A good machine shop
will balance the pressure plate separately and give you
all the balance specifications so if you need to replace
something down the line you can reproduce the balance
of that component. |
(Short Block Assembly) |
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