Anthony,
A variation of this question came up recently. On 10/11/02 I posted the
following to the List:
The simple answer is, there is no difference; at least the blocks all
started out the same. The story is that the HiPo blocks were hand picked for
cylinder wall thickness, etc. The difference is in the machining of the
blocks; bigger main caps, screw-in oil galley plugs, etc. Here's a link to
rundown of the HiPo block's unique features.
http://members.tripod.com/lyc_42/fordv8/hipo/hipo.htm
As to the question of using mechanical lifters, the same considerations also
hold for HiPo and non-HiPo engines. First, you do not have to adjust them
with the engine running. With cast iron heads, it's best to adjust them with
the engine warm, but not necessarily hot. If you have aluminum heads, which
expand more with temperature than the push rods, you need to adjust them
hot. Or better yet, measure one hot, then let it cool to a comfortable
temperature and measure it again and factor the difference into the
adjustment.
The interval between adjustments depends on several factors. If you use jam
nut (Polylock) type rocker arm locks, this will ensure they won't move. This
leaves wear as the reason valve clearance increases with running time. Using
roller rockers reduces friction and wear. After the initial break-in, you
may be able to go about 5k miles between adjustments. I'd check it every 2k
or so just to be sure. I've never seen an adjustment get tighter with
running time, and you can hear a lifter when it's more than two or three
thou loose.
You won't be able to remove the left side Tiger or other finned aluminum
valve covers without lowering the engine, especially if you use roller
rockers. For a street machine, a hydraulic cam is usually preferred and
there are many good choices. I recommend a cam like the Ford Motorsport
M-6250-E303 or, my favorite, the Crane PowerMax H-278-2 Hydraulic, Dual
Pattern. Here's a link to the Crane Web page:
http://www.cranecams.com/motorsports/ford/363801.htm
Here's link to a list of small block Ford cams and specs:
http://www.jason.fletcher.net/tech/camlist/cams_rol.htm
Good luck.
Bob Palmer
rpalmer@ucsd.edu
rpalmer@brobeck.com
rpalmerbob@adelphia.net
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