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An examination of the piece indicated a radical new design as depicted in the
photograph. As Ralph states, the goal of the design was to improve the air
flow distribution to all cylinders, thus evening out the power generated from
the engine. This is accomplished by changing the air flow path into the manifold
by means of a physical design change. The new design incorporates a 90 degree
turn with a narrow opening into the intake manifold. As Ralph stated, "This
design makes the intake manifold think a throttle body is sitting directly on
top of it." Ralph also claims his efforts were justified on both a
flowbench and on an engine dyno., although I did not have the results.
All of this sounds interesting, but the proof is in the performance, so off
to the drag strip I went. The baseline performance was with the
"stock" upper plenum installed. I say "stock"
meaning that the previous
owner had reshaped the interior of the plenum in order to gain better flow and distribution, but
no flow bench or dyno. data were available for these modifications. The
results of the three baseline runs are given below:
RUN 1: 9.63 seconds at 144 mph
w/ a max. EGT of 1580 deg. F
RUN 2: 9.58 seconds at 145 mph w/ a max. EGT of 1598 deg. F
RUN 3: 9.68 seconds at 144 mph w/ a max. EGT of 1572 deg. F
The next set of runs were made on the same day with the only change being the HEMCO upper
plenum.
As was the case with the baseline runs (RUNS 1-3), the launch was at 15 psi. with a maximum boost level limited to 24
psi. The results with the plenum change are given below:
RUN 4: 9.51 seconds at 145
mph
w/ a max. EGT of 1606 deg. F
RUN 5: 9.47 seconds at 145 mph w/ a max. EGT of 1600 deg. F
RUN 6: 9.45 seconds at 147 mph w/ a
max. EGT of 1610 deg. F
The data indicates
that the HEMCO upper plenum did increase the performance of my car. In reviewing the data It
is more important to evaluate the performance increase based on the
trap speed since the elapsed time can be affected
by many
variables, whereas the trap speed can be directly related to
the engine power output with common mathematical
formulae. As the data indicates, the HEMCO upper
plenum increased the trap speed by approximately 1.4 mph on an average of
three runs.
It should also be noted that my original
upper plenum had been modified to increase
its performance, hence, if compared to a completely stock upper plenum, the gain in performance would probably be more pronounced. Overall, it appears
that the HEMCO upper plenum would be a
welcome addition to any motor with more
benefits realized with a greater amount
of engine modifications. If you are in
the market for an upgraded upper
plenum, then you should call Ralph at
HEMCO for some additional information.
The plenum accommodates the stock throttle bracket via a special bolt which is supplied. All
other bolts and studs required for installation
are also included.
The upper plenum's price is $229.95 (+shipping).
It is available in 58mm and 62mm versions.
P/N V6PK158 for the 58mm version
P/N V6PK162 for the 62mm version
It can be purchased directly from Hemco Machine,
Inc. (See addressed and phone numbers above) or through the following distributors:
White Racing & Marine
12820 E. Nine Mile Rd.
Warren, MI 48093
Phone: (810) 756-3026
Fax: (810)756-8350
Visit White
Racing & Marine
Reprinted With Permission
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