Camshaft and Lifters
Overview
For a carburated 302 to make 400 naturally aspirated horsepower
it is going to take a cam which is extremely efficient
in the 4000 to 7000 rpm range. We'll be using World
Windsor Sr. heads which are up to the task of flowing
well at high rpms, but we need a cam to match. We turned
to Crane Cams to help us select a cam that will support
the power range we are targeting.
Crane recommended a solid roller cam from their Powermax
series . We ended up going with a complete valve train
assembly from Crane. We've always found the best results
when you stick to the cam manufacturers recommended springs,
retainers, lifters, etc. This not only guarantees everything
is going to go together right the first time, but also
that all the parts have been engineered to work together.
This is extremely important when you are building a high
revving race engine which cannot tolerate any amount of
valvetrain instability.
Crane's mechanical roller-tappets (part no. 44542-16)
The link bar design eliminates the need for stock retainer
hardware.
Selection
The Crane S238 is a mechanical roller cam with 238 degrees
intake duration and 246 degrees exhaust duration, with
110 degrees lobe
We'll use an aggresive profile
solid-roller cam.  |
separation. Lift is .560" and
.579" respectively. As with any solid cam (flat tappet
or roller) you have to account for the valve lash, which
in this case is .020". This means that in terms of operating
specs, the cam will have .540" lift intake and .559" lift
exhaust. Because of the .020" lash, duration drops roughly
10 degrees to 228°/238° respectively.
While some folks may think this is a big cam, we think
it is really not all that big. In fact it should be just
right for what we are after! The basic rpm
range is from 3000-6500 rpms, and with the good heads
and single plane intake, we should be able to stretch
out the peak to near 7000 rpm. The advantage of a mechanical
roller cam is two fold. First of all roller cams make
more power being that the roller tappets generate less
frictional losses as compared to flat tappets. However
the real performance benefits to roller tappets is that
their base is of infinite diameter. A flat tappet lifter
has a machined base which can only "ride" the cam lobe
for so long, whereas the wheel of a roller tappet can
follow very aggressive lobe lift and ramp rates. Finally,
the benefit to mechanical lifters, be it roller or flat
tappet, is that they have a higher rpm potential over
hydraulic tappets. A mechanical tappet has no valving
which can "pump up" and create power loss during high
rpm valve float.
Installation
Some engine builders prefer installing the camshaft in
the block before
Installation for roller cams
requires only oil. |
the pistons and crank go in.
It doesn't really matter, so long as you do it right!
The key is to slide the cam in slowly so as to avoid nicking
the cam bearings or cam lobes. Using a long bolt as a
handle helps ease cam installation.
Roller cams do not require a break-in period so really
all you need is to generously oil the lobes and slide
it in. Moly is not necessary, but wont hurt. Flat tappet
cams, however, do require moly lube due to the high friction
during the initial break-in of the lifters to the cam
lobes.
Due to the link bar design of Crane's solid roller lifters,
there is no need
Linkbar solid-roller lifters
are installed with engine lube. |
to use the stock guide bars
and retainer. The lifters must be installed with the link
bar facing the center of the block. We dipped the lifters
in oil, and coated the lifter
bore with a little moly prior to installation. If you
are going to run a flat tappet cam, be sure to use plenty
of moly on the lifter face.
Degreeing
Anytime you order a custom camshaft it is good practice
to check that it was ground to the correct specifications.
This verification process, known as "degreeing"
is not too difficult to learn and is a must in any performance
engine builders set of skills. Our tutorial on Degreeing
a Camshaft in the Fundamentals section of the Tech
Department will take you through the fairly simple process.
|
 (Oiling,
Cooling, and Fuel) |
| |
|
|
|
|
|
Crane
Mechanical Roller Cam
