I have learned to be cautiously
pessimistic about dyno results. It is human nature, especially
in this hobby, to make predictions about what  sort
of power your car is going to put down on the dyno. Yet
having been dissapointed by the big red rollers more often
than not, I have trained myself to guess low, and therefore
leave the shop with, hopefully, better than expected numbers.
It's pathetic, but it spares a lot of heartbreak when
you make 50 horse less than you boasted to your buddies!
When it came time to get our 5.0L, ala AFR 165 heads,
to the dyno, I played the same mind game on myself. However
before I reveal my predictions, let's go over what got
us to this point.
A while back we reviewed
and flow tested AFRs 165cc small block Ford (SBF)
cylinder heads. These were actually one of the few heads
we were not able to test a few years back when we performed
our major
show down of SBF heads. As anticipated the AFR heads
were serious contenders. If one discounts the Trick Flow
head's larger intake runner and valve, and revised valve
angles, the AFR head is the clear king of the street-head
mountain, at least in the cfm category. At .500"
lift the heads flowed 238 cfm on the intake side and 182
cfm through the exhaust. However in typical FM fashion
we're after true gains on real world Ford muscle cars.
The meant an obligatory dyno test with the heads installed
on a test vehicle.
We decided to put the heads on a relatively stock 5.0L
engine. FordMuscle has a new project car in the stable,
the authors own 1993
Cobra (see '93
SVT Cobra in the Project Cars section.) The rare first
year SVT snake was procured in bone-stock form, with 82,000
ticks on the odometer. The 5.0L Cobra motor is a about
a 25 horsepower bump up from the stock 5.0L HO Mustang
motor. The gains are largely attributed to the iron GT40
cylinder heads. Ford also modified the cam, used 1.7:1
rocker arms, and tweaked the air-fuel delivery to match.
In stock form these cars put out roughly 220 horsepower
at the rear-wheels. The challenge then would be to bolt
on nothing but the AFR 165 heads and see what results.
To get a true understanding of the capabilities of these
well touted heads, we installed the heads with the stock
'93 Cobra camshaft. The
A ported Cobra lower intake
was sought out to help match the larger intake runners
of the AFR 165cc heads. |
cam specs are roughly 210 degrees
duration and .479" lift with the factory 1.7:1 Cobra
roller rockers. We did retard the cam four degrees to
move the power band up slightly and take advantage of
the high-lift flow potential in these heads. The other
changes to the engine are a ported Cobra lower intake
manifold, underdrive pullies, and a larger mass air and
throttle body. The exhaust on the car consists of shorty
headers and a Mac Prochamber h-pipe running through the
stock mufflers.
We installed the heads over a weekend without any major
glitches. The AFR heads, in addition to being well designed,
are truely a bolt-on head. We had no intake or exhaust
manifold alignment issues. All that was required were
a set of new, hardened, pushrods in the stock length.
A couple weeks later we had the car to the dyno.
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 (Dyno
Results) |
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In
This Article:
With the AFR 165 heads proving themselves on the
flow bench, we decided to install the heads on
a 1993 Mustang Cobra motor, with no other major
changes. The car is then tested on a chassis dyno.
Also See:
Part
One: Flow Testing AFR's 165cc Head |
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Our AFR 165cc heads are set up
with 1.90"/1.60" valves, 59cc combustion chambers,
dual springs, and 7/16" studs. |
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The stock '93 Cobra GT40 heads
are removed, note the factory equipped 1.7:1 pedestal
mount rockers. |
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The heads are torqued down, and
new Crane 1.7:1 stud mount rockers are installed with
hardened pushrods. |
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The stock Cobra cam is left in
place but retarded 4 degrees. The lower intake is ported
to match the FelPro 1250 gaskets. |
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Hedman shorty headers replace
the restrictive stockers. |
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