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C.Asaravala and Rufus Crow, III.
The Glass Half-Full
Having your car stolen sucks. Having it recovered sucks more
- especially if you choose to rebuild it. It's not that bringing
the car back to some resemblence of its former state is a
bad thing. It's just that you find yourself angry and bitter
over having to redo the things you had already spent time
(and money) to do before. The glass half-full optimists would
cheerfully remind us however that these are opportunities
to do things better, perhaps even learn new things along the
way. So while it's a bit hard to look at the violated Cobra
as anything but an example of how the glass is not only half
empty but darn right broken into razor sharp shards, we're
going to try to look at the upside.
Prior to the Cobra being stolen we had upgraded
the heads and various underhood induction parts to produce
303 horsepower and 340 lb.ft. of torque at the rear wheels
- very respectable for a stocl 5.0L bottom end and cam. The
crooks quickly took notice of the aftermarket goods and, to
our bewilderment, went through the effort to remove the aluminum
heads and install a set of original 93 Cobra GT40 heads. Unfortunately
the AFR heads and other parts of value were never recovered,
but that is the basis for the opportunity to install another
set of heads.
As we detailed last month, FM pal Rufus Crow III is the new
owner of the Cobra. Rufus quickly shored up the issues with
the Cobra and got it in decent running condition. With the
stock GT40 heads and Cobra intake it produced 260
horsepower and 300 ft.lbs. of torque. A decent baseline
to start building from.
New Heads Again
This time around we decided to give the new RHS heads
a shot. The heads have gained immense popularity ever since
Comp Cams stepped in and purchased Pro-Topline, the stuggling
New Zealand cylinder head company which originally brought the
heads to market. We first reviewed
the RHS heads several months ago and were very encouraged
by their stellar "as-cast" flow numbers. The RHS 180cc
head flowed 270/214 cfm (intake/exhaust) at 0.535" lift.
Since the plans for the Cobra are centered around autocrossing
and opentracking, we justified that a larger runner would be
the ticket to getting a higher powerband and keeping the engine
in gear longer.
Big Valves are No Problem
The only concerns we had with the RHS line up of Ford heads
(180cc, 210cc, and 215cc) was that the three heads are all
equipped with 2.02" or larger intake valves. That means
piston-to-valve clearance issues for a stock bottom end. We
brought this up with RHS' manager Kevin Feeney who agreed
and hinted there may be a smaller head in the works.
Many guys often pass up stellar heads, and the subsequent potential
for power, because they believe big valves means big headaches.
This absolutely isn't true as we're about to show you. Using
a crafty tool from Isky Cams (side bar) anyone can cut machine-shop
quality valve reliefs into their pistons without ever removing
them from the block, nor the block from the car. In fact the
technique we're about to show you isn't just for big valves,
but just as applicable if you want to run a camshaft with significant
lift and duration and find yourself with insufficient clearance.
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RHS
180cc Flow Data
"Did you just say we're gonna cut into my pistons?!"
That's right, we're going to cut deeper and wider valve
reliefs into the stock pistons while they are in the block.
The stock Ford 5.0L pistons in 1993 were hypereutectic
and not forged as in previous years. The valve reliefs
are just adequate for a 1.84" stock instake valve.
Depending on the lift of your cam you might be able
to get away with a larger than stock valve. However
it's always wise to check. Usually with a larger diameter
valve the interference is on the outer edges of the
valve relief in the piston - because it isn't wide enough.
We like to dab some red latex paint onto the valve face
and then put the head on the block. Push the valve down
until it contacts the piston.
We pushed the valve against the piston to transfer the
red paint and create a "witness mark". Our clearance
was insufficient at just .040" on the intake side.
You can see where the larger 2.02" valve hits on
the outer edges of the stock valve relief. This clearly
indicates that we'll need to cut a much wider notch in
the piston. Next we'll determine how deep to cut the notch.
