18 ENGINEBUILDERmag.com | AUGUST 2020
valve design. “ ese are inline valves, but I look
for them to run every bit as well as the canted-
valve. To be quite honest, our forte has been to
beat the canted valve stu with inlines. We’ve
done a good job with that over the years.”
According to Williams, they build heads for
a lot of drag racers, but their bread and butter
is sprint cars. “We’ve dominated the 410 class
over the years and the World of Outlaws. We
probably do 99% of all those in the world. It’s
a big marketplace for us. e 360s have a spec
head rule, so we don’t play in that sandbox.”
Some engine builders prefer to buy bare
cast heads so that they can do their own port
work. However, CNC ported heads from
manufacturers such as AFR, and others are a
more signi cant chunk of the market. We think
some of that is due to enthusiasts who buy
heads that are already assembled and ready to
bolt-on, but engine builders are also purchasing
these heads because it can speed up the rebuild
process.“ e bulk of our sales is fully CNC ported
cylinder heads,” says AFR’s Torrecarian.” Porter’s
castings are still available but are only a fraction
of our overall sales. Also, we do quite a bit of
private label heads.”
When it comes down to choosing or
comparing cylinder heads, the best way is to
bolt them on and make some dyno pulls. e
one that makes the most peak power may not
always be the best choice if the rpm range is
very narrow. You may want a head that delivers
a broader range of power and torque. If the
engine is for the street, your customer might
wish to have a broad, at torque curve with
more low and mid-range torque to quickly get
o the stoplights.
Another thing to consider in boosted
applications is to use Inconel exhaust valves and
heavy-duty intake valves for the high cylinder
pressure. Many power adder applications
accelerate quickly and require extra spring
pressure. Many manufacturers recommend
upgrading valve springs or increasing valve
spring pressures because the boost can reduce
spring tension. AFR says that even 15 lbs. of
boost on a 2.125 ̋ valve can reduce the closed
seat pressure of the spring by 40-45 lbs.
Air ow depends on valve lift, valve area
and air density. Using a ow bench can help
you understand these values, but keep in mind
that these values can vary from one ow bench
to another, depending on the methodology
and equipment used. Flow benches can have
a margin of error of about one percent plus or
minus. With a cylinder head that ows 400 cfm,
the margin of error could be plus or minus four
cfm.
Flow numbers at peak valve lift may be
useful for bragging rights, but usually, it is more
important how well the head ows at partial
valve lift as the valves are opening and closing.
Better ow characteristics at partial valve lift
can have more of an e ect on power and torque
than big air ow numbers at peak lift.
Accurate cylinder head comparisons mean
you should look at the entire ow curve if
possible, from low lift to maximum lift. If you
do that, you will have a better picture of how
the head will perform on the engine you are
building. EBCYLINDER HEADS
Flow numbers at peak valve lift may be useful for bragging rights, but usually,
it’s more important how well the head fl ows at partial valve lift as the valves
are opening and closing. Be er fl ow characteristics at partial valve lift can
have more e ect on power and torque than big airfl ow numbers at peak lift.
14-18 eb.aug20 Cylinder Heads.indd 18 8/7/20 9:44 AM
Naresh Jariwala