~FLATHEADS~
1. OVERVIEW & HISTORY                7. IGNITION
2. FUEL FLOW                                8. INDUCTION
3. HEADS                                       9. EXHAUST
4. CAMSHAFTS                             10. LUBRICATION   
5.
CRANKSHAFT
6. RODS & PISTONS
FUEL FLOW  
OK, so lets say that you’re like author and comedian Steve
Martin in his book “Cruel Shoes” – funny book in which
there’s a chapter on “How to be a Millionaire”. Steve starts
out the chapter with the revelation that in order to be a
millionaire, first you have to get a million bucks. Pretty
clever. So you want to build a Flathead V8 race engine?
First, you have to get a usable flathead block and although
it sounds simple, that’s not always the case. So let’s say
you have that good, nearly crack free (most blocks have
cracks in the deck surface between head bolt threads –
‘stress relief’) block and have it disassembled and
degreased. Where next?
First - fuel flow. Ford designed the engine with a generous
'transfer area' in their head allowing the fuel air mixture to
exit the port of the intake valve and then make it's turn
down into the combustion chamber. Fuel-air mixture, like
anything that has mass, doesn't generally like to change
direction once it's moving and in the flathead arrangement
it's actually has to make two 90 degree turns prior to
entering the combustion chamber. Now every racer likes a
challenge and here's a good one. Coupled with this
problem is the low compression of the arrangement. That's
easy right? Just cut down the area of the valve pocket and
transfer area thus reducing the volume over the
combustion chamber and you have more compression.
Performance head manufacturers of the time did just this
in reducing the transfer area. So now you have your
compression up and have created two more problems, one -
less flow and two - more heat. Make the heads out of
aluminum which will help dissipate the heat better and
that takes care of one problem. Fortunately, the guys
making the aftermarket heads of the time were savvy and
built their heads with greater water capacity as well as of
rugged thickness to combat other issues. Still doesn't help
fuel flow and so here's where the racer had to come to a
compromise between flow and compression. You rob Peter
to pay Paul and 'relieve' the block under the head transfer
area to regain some flow, thus losing some compression.
Not to worry, there’s other ways to get that back and you
have to have flow to make power. You'll also want to get
those ports bigger to increase your flow so grab your
electric drill or die grinder and start lightening that block,
there's plenty of work to do. In talking with Barney Navarro
a few years back, he related that the most important place
to remove material from the intake port was in the top of
the port, or the short runner. I took his advice and have
found he was correct, based on performance at the track. I
now leave the bottom of the port alone aside from polishing
and leave the ‘kickup’ around the valve stock. After all, this
is part of what helps the fuel-air mixture make one of its
turns. Don’t worry about a matte finish, as described
before, the mixture goes through such a turbulent path
that atomizing is no problem, I polish mine to look like a
spoon. As your porting out the intake runner in the block
though, take care as to not go far and hit the water jacket,
this can create some problems so just take this advice and
don’t do it. Treat your exhaust the same way – think of
yourself as an atom trying to get in or out of the chamber. I
put my valve guides in and contour them to the port, and
take out any material that creates an obstacle to the flow.
There’s plenty of material to remove here, Bob Hayslett
once told me he figured he took ten lbs. out of the block
when porting, he may have been exaggerating but then
again, maybe not. OK, so you’re ported and polished, now
how about relief? Several theories here, new thinking is
that the relief does nothing to increase flow. From my
experience, I have to disagree, my best engines have all
been relieved.
To do this first it’s best to have a baseline for where the top
piston ring ends up while the piston is at top dead center.
Assembly and some blueing are required to get this exact,
a good rule of thumb is 0.125 depth for relief, some do
more and some less, again it’s a cut and try issue. Next, lay
a head gasket on the blued deck surface and scribe out the
contours of the chamber on the transfer area to be
removed. The next step is really important – place your
guide in the block and then get an old valve and permatex
it in place. This will protect the valve seat as you start
grinding which is important; in fact, always take care of the
valve seat, a few careless whacks on it can cause you
problems later. Determine if your relief is to be a ‘full’ or
‘half’. A full relief opens the transfer area for both intake
and exhaust while the half only opens the intake. Since
exhaust only needs to flow approximately 65% of intake,
many used the half relief to help maintain compression. I’
ve used both with success. At this point start carefully
removing material from the deck surface in the marked out
transfer area and check your work with either a depth
micrometer or caliper. Smooth out all sharp edges and
polish with tapered roll sandpaper using either a die
grinder or electric drill. Take your time. A good port and
polish job comes from patience, experience and willingness
to take a chance. You can’t win if you don’t play. It’s not a
bad idea to practice your technique a bit though on one of
those junk blocks you found that didn’t make the grade for
your build. Next we go to the
head.
Stock 8BA Transfer
Area.
Evans Transfer
Area.
Stock
Port.
Aggressive
Port.
Port & Relief areas
(shaded).
Half
Relief.
Full
Relief.