A
few months back we featured
the 351 4V Cleveland powered 1973 Torino, owned by FM staff
member Jon Mikelonis. We didn't reveal too much about the
engine in that article because we knew we would have plenty
of opportunities in future coverage of that car. Well here
we are, as we anticipated, with a detailed cam swap project
for the Torino.
Most camshaft swaps are presumed to be "step ups",
in that there is an increase in the camshaft size in hopes
to gain power. Well we're doing the opposite in this cam swap
project.
Our 351 Cleveland was originally built with road racing in
mind. A set of 4V heads were rounded up and converted to stud
mount adjustable rockers. A custom ground solid (flat-tappet)
cam was ground by Ultradyne. Duration was ground as 243/251
@ 0.050" lift. The generous lift specifications (0.617
/ 0.642) were set to match the high-rpm and lift requirements
of the big ported 4V heads.
The engine made in the neighborhood of 480 horsepower, with
a Holley Strip Dominator intake and 1050 cfm Dominator carburetor.
As expected, the power range was between 4000 and 7500 rpm,
suitable for a flat-out 100 mile road race such as the Silver
State Classic, but not quite practical for the quick jaunt
to the supermarket.
Don't get us wrong however, our objective here is not to make
this a tame motor. It is just that the objective of the car
has changed. No longer is the car destined for wide open throttle
road racing. Instead the car has become more of a nostalgic
restoration - a car that retains all the factory looks, but
has some tasteful and period-correct modifications, including
those in the engine department.
With
the new, more subdued, duties for the Torino, it made sense
to tone down the engine. While ideally we should replace
the 4V heads for the more streetable 2V or Australian 2V
counterparts, we simply did not want to spend that much
time with a head swap. Instead we contacted Crane Cams and
had them suggest a hydraulic flat-tapped camshaft which
would offer good mid range power and a fairly broad torque
curve.
What
we ended up going with was the Crane Powermax H-288-2 (pn:
524421), The cam features a split duration pattern of 226
degrees on the intake and 230 degrees on the exhaust lobe.
Lift (at 0.050" lobe lift), with 1.73:1 rockers, is
.528" / .536" respectively. However because we
are using 1.80:1 Crower rocker arms, the lift will actually
measure .549" and 0.557")
Comparing
Cam Specs
 |
|
Before
(Ultradyne)
|
After
(Crane)
|
| Cam
Part # |
Custom
Grind
(NF54/NF52 lobes)
|
524421
(Powermax H-288-2)
|
| Lifter
Type |
Solid
|
Hydraulic
|
| Duration
@ 0.050 |
243/251
|
226/230
|
| Lift
(1.73:1
rockers) |
.617/.642
|
.528/.536
|
| Lift
(1.80:1 rockers) |
.641/.668
|
.549/.557
|
| Lash* |
0.020"
|
--
|
| LSA |
108
|
112
|
|
|
|
|
When
comparing a solid cam to a hydraulic, it is important to take
into account the lash requirement for the solid cam. In general
lash will reduce the effective duration about 10 degrees,
and reduce the lift by the amount of the lash. Looking at
our Ultradyne custom cam, the lash of 0.020" would result
in approximately 233/241 duration and 0.621"/0.648"
lift. Comparing this to the new cam shows a pretty radical
change, especially in the valve lift, where we will be giving
up 70 and 90 thousandths on the intake and exhaust valves
respectively. This will certainly drop the powerband down,
and what was once a near 8000 rpm engine, will be limited
to 6500 rpm. The 112 LSA of the new cam will also help in
flattening out the power band. Continue
|
