Intake Runner Improvements
Improving flow with the constraint of retaining the same
intake runner volume only leaves one option: change how
the air moves through the runner.
The objective is to get more air through effectively the
same physical area. To do this AFR reshaped the roof of
the intake runner and cleaned up how it transitions around
the valve guide boss. Compared to
The AFR165cc Comp porting
package features reshaped intake bowl and guide
areas. |
the standard AFR 165cc head,
a glance down the new intake port reveals a much longer
"air foil" taper along the roof leading up to
the guide. The tear drop shape around the guide itself
is more aggressive, and the wing shape runs past the back
side of the guide leading into the long-side radius. Also
improved is the short side radius. The turn is laid back
resulting in less turbulence and a straighter shot into
the bowl area. All told the changes to both the intake
and exhaust side add an additional hour-and-a-half to
the normally two hours it takes to complete the standard
165cc head. The increased CNC time is also a result of
finer cutting levels and less tool deflection. Anyone
who is familar with AFR heads has seen the concentric
ridges throughout the runners. On the Comp package
heads these ridges are less pronounced.
The result (see Chart 1) of the additional CNC porting
is valuable flow gain in the .400-.600 thousandths valve
lift range. The standard 165cc head hits flatline at exactly
half-inch lift. While this was fine for stock or mild
cam applications, it put street guys wanting the low to
mid .500" lift cams in a predicament. Many aftermarket
5.0L cams are ground with over .500" lift but conservative
duration numbers to keep the EFI computer happy. These
aren't high reving motors and if a guy steps up to the
AFR 185cc head he may struggle with the low end torque
loss due to the large runner volume. With the Comp package
head we get the flow above .500" and there is even
an improvement at the low lift points. The average flow
between .200 to .500" lift calculates to 201.5 cfm
which heartily beats our results of the Trick Flow Twisted
Wedge head, which previously
edged out the standard AFR 165cc head 199 cfm to 194 cfm
Even more remarkable is this is still done with stock-piston
friendly 1.90" intake valve.
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Greater Exhaust Flow
Competition package exhaust
port. |
Standard 165cc exhaust port. |
The first impression the Comp
head makes is its' square exhaust ports. This is straight
out of Tony Mamo's playbook, and a bold departure from
the hallmark D-hole exhaust port on the standard head.
The pressure of the exiting gasses forces flow against
the roof. By raising the port ceiling and opening up the
area around the guide, turbulence is reduced and the chamber
is evacuated faster. Also contibuting to the gains are
enhancements to the valve job for the Comp package 165
head. All told the flow gains are huge. From just .200"
lift the head is flowing 10% better than the standard
predecessor. Keep in mind that the 185cc older brother
shares the same exact exhaust runner as the 165cc head.
It is rumored that eventually the 185 will also be offered
with a Comp package, but for now this means the 165cc
Comp exhaust port will outshine that of the 185cc head.
This puts the head in interesting territory for forced
induction and nitrous motors. Considering that many 5.0L
enthusiasts are shopping for emmisions compliant parts,
including blowers, the 165cc Comp head with its big exhaust
flow is a great option. It is emmisions legal, wont require
piston notching for guys sticking with mild cams, and
the 79-80% exhaust-to-intake flow ratio is ideal for purging
the big boost volumes from the combustion area.
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The Bottom Line
AFR heads have never been the cheapest heads on the
market, but they are likely the best engineered. The standard
165cc head retails at around $1300, putting it a couple
hundred above its major competitors. The Competition porting
package adds another $300 to the ticket. A $1600 expenditure
on a set of small block Ford heads is pricey, but consider
that many guys eventually exceed that cost by sending
out an inferior aluminum head for porting to get the flow
numbers into respectable range. We've done it ourselves.
AFR anticipates this head will be a hit amongst guys who
are not willing to leave any power on the table. We believe
it will also be a popular choice for those of you building
302 to 331 cid motors looking for broad, table flat, torque
curves and yet good peak horsepower in the 6000 rpm range.
Either way it is surely a solid investment that will be
tough to beat for a long time time to come.
We have yet to see live results with this head due to
its newness, but some early engine dyno testing performed
by AFR on a mild dual-plane 302 motor showed 8-10 horsepower
across the board over the standard 165 head. The intake
manifold was noted to be potential choke point with the
new Comp heads, and porting or at least port matching
the intake to the heads will be highly recommended to
take advantage of the flow potential. We will conduct
our own comparision in the near future, look for an article
soon.  |
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Rob Jr. from Rob's Auto Machine
in Hayward, CA get' the new AFR 165cc head mounted on
the flow bench. Heads were flowed at a standard pressure
of 28" H20, using a 4.030" bore fixture. A
radiused inlet was used on the intake port, while no
exhaust tube was used. An exhaust tube, used to simulate
a header, would have increased the flow numbers by several
cfm. |
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Flow Bench Results
Intake Flow @ 28" H20 |
| lift (in.) |
Std. 165
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165 Comp
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.100
|
60
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63
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.200
|
125
|
132
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.300
|
188
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191
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.400
|
226
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235
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.500
|
238
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248
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.600
|
248
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258
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Flow Bench Results
Exhaust Flow @ 28" H20 |
| lift (in.) |
Std. 165
|
165 Comp
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.100
|
52
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54
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.200
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100
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111
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.300
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142
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156
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.400
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168
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187
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.500
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181
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199
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.600
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189
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201
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Sources
|
Air
Flow Research Heads
10490 Illex Avenue
Pacoima, CA 91331-3137
818-890-0616 |
Rob's
Auto Machine
Industrial Blvd.
Hayward, CA
510-732 1909 |
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