text and photos Dan Jones
First Test
CHI 3V Heads,
Scott Cook Intake
CHI 3V Intake
The CHI 3V 225cc cylinder heads and matching Scott Cook dual plane intake were provided
by Phillip de Cadenet and the CHI 3V single plane intake was provided by James Kayser.



The first cylinder head and intake combination to be tested was the CHI
3V 225 cc heads coupled with a Scott Cook aluminum low rise dual plane.
Both parts are imports from Australia and are very nice castings. Scott's
intake manifold looks much like a Ford cast iron DOAE-9424-L dual plane
but is cast in aluminum, slightly taller (around 10 mm or a bit more
than 3/8") with smaller ports that are sized to fit either the CHI 3V
heads or a 4V head with stuffed intake ports (raised floor). Compression
was a little under 10:1 with the CHI heads. All pulls were made on 93
octane (midwest winter blend) pump gas and, unless otherwise noted, all
pulls were made through mufflers. Also, the atmospheric conditions were
measured and all dyno numbers corrected to standard day conditions.
The headers for the first pulls were Hooker Competition units with 1 3/4"
diameter by 27" long primaries, 3" diameter by 8" long collector (probably
part number HOK-6920HKR for 4V heads in a '67-'68 Mustang). Mufflers
were Magnaflow 3" inlet and outlet. The dyno carb was a Holley 950HP
(without air cleaner or inlet bellmouth) and we had an Innovate LM1 wide
band O2 sensor keeping an eye on the air-to-fuel ratio. The engine had
been previously run in for around an hour to seat the rings. It was run
for a few minutes to warm the oil to operating temperature and the initial
pulls made to set the total timing. Total timing settings from 32 to 38
degrees were tried. Unlike our previous dyno tests of a 10:1 compression
408 cubic inch Cleveland with closed chamber iron heads which made it's
best power at only 32 degrees of total timing, this engine made it's best
at 38. However, some trace detonation was detected by the knock sensor
in the mid range. Rather than re-curving the distributor at that time,
we opted to pull the total timing back to 33 to 34 degrees. We lost
around 5 HP but gained some safety margin.

Before the first recorded pulls, Dave guessed we'd make around 400 HP
with the dual plane and pick up 20 HP with the single plane. Sure enough,
the Cook dual plane intake/CHI 3V combo made right at 400 HP and 400 ft-lbs
of torque. This dropped to 395 HP with the timing set back. Switching to
the single plane CHI 3V intake manifold picked up 20 HP, just as Dave had
predicted. The pulls were started at 3000 RPM and the HP peaks were near
6000 RPM. We ran both intakes to 6500 RPM and the horsepower stayed
constant with no signs of dropping off. With the previous 408C which used
the same dual valve springs, horsepower began dropping at 6000 RPM no matter
whether we used the link bar Crane lifters or the OEM Ford lifters. Both
of the initial test combos had nice flat torque curves that hung around
400 ft-lbs so I think we guessed right on our cams specs. The CHI single
plane looked to have the edge from around 3000 RPM on up but the CHI is a
rather tall intake that won't fit a lot of places the low rise Cook intake
will. The Cook intake also has the edge in the sleeper department. Paint
it with some dark Ford blue and no one would know it's not a cast iron Ford
intake. Interestingly, the Cook dual plane did not have the distinct dual
resonant peaks the dual planes on our previous 408C exhibited.

We next tried a set of large tube Econo Altered drag headers which have
2 1/8" primaries of around 40 inches length and long 4" diameter collectors.
These were run without mufflers. Our mild street 351C was just not enough
engine to make use of these headers. They lost a whole bunch of torque and
didn't catch up until 6000 RPM. We then tried a set of Pantera 4-into-1
headers (Hedman style with 2V port openings). These have rather short
primaries (between 19" and 24") of 1 3/4" diameter and a tiny collector with
2 1/4" outlet. They lost maybe 15 ft-lbs but closed the gap some as RPM went
up. Overall, I don't think they worked as well on this engine as the Euro
GTS style Pantera headers had on the 408C. Those headers have a 2" primary
with similar short primaries but have a tri-y type collector. It would be
interesting to experiment with a better collector on the Hedman headers to
see what sort of improvement can be made. The stock Pantera ANSA mufflers
were just plain terrible. Just as the Euro GTS mufflers had on the 408C,
the stock Pantera mufflers lost 50 ft-lbs and 50 HP to the 1 3/4" long
tube Hookers with 3" Magnaflows. Anyone got a set of 1 7/8" primary long
tubes to lend us? 1 7/8" might be better on this engine.

We attempted to try a small 4180 Holley (CFM rating in the 585 range) to
see how much HP we would lose with the reduced carb flow but we ran into a
delay. The 4180 uses a different style bowl gasket which we didn't have
on hand. As we hadn't had anything to eat or drink since breakfast, we
decided it was a good time to knock off for the day. Dave noted that,
given the number of pulls we made, it looked like the engine had pretty
decent fuel economy. I also opined that the torque band should be a good
match to the gearing of the Pantera. Dave said he'd pick up the 4180
gaskets and we'll give that a try later. Also, we plan on trying 1.65:1
roller rockers on the exhaust side before moving on to the next set of
heads. We may also try the Parker Funnelweb on the CHI 3V heads if the
port mismatch is reasonably close.

Dave has the specifics of all the pulls recorded on his shop PC, along
with the cylinder head and intake manifold flow bench results. When he
sends those to me, I'll enter them into a spreadsheet and update this
post with the relevant data.

Dan Jones