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GT40 Aluminium Head Flow Tech by Peter L. Turek
GT40 aluminium head flow summary (11/23/96 and 12/06/96)
Intake CFM flow chart
---------+--------+--------+--------+--------+--------+---------
Valve | | | | | | |
Lift | .100" | .200" | .300" | .400" | .500" | .600" |
---------+--------+--------+--------+--------+--------+---------
stk GT40 | | | | | | |
intake | 64 | 127 | 180 | 190 | 210 | 202 |
---------+--------+--------+--------+--------+--------+---------
ported | | | | | | |
intake | 83 | 146 | 204 | 234 | 246 | 250 |
---------+--------+--------+--------+--------+--------+---------
Stock Vs. porting on intake
CFM Inc. 19 19 24 44 36 48
% Inc. 29.69% 14.96% 13.33% 23.16% 17.14% 23.76%
Exhaust CFM flow chart
---------+--------+--------+--------+--------+--------+---------
Valve | | | | | | |
Lift | .100" | .200" | .300" | .400" | .500" | .600" |
---------+--------+--------+--------+--------+--------+---------
Stk GT40 | | | | | | |
exhaust | 58 | 108 | 144 | 153 | 156 | 159 |
---------+--------+--------+--------+--------+--------+---------
Ported | | | | | | |
Exhaust | 80 | 122 | 158 | 188 | 194 | |
---------+--------+--------+--------+--------+--------+---------
Stock Vs. porting on exhaust
CFM Inc. 22 14 14 35 38
% Inc. 7.93% 12.96% 9.72% 22.88% 24.36%
Intake-to-Exhaust ratio Chart
---------+--------+--------+--------+--------+--------+--------+--------
Valve | | | | | | |
Lift | .100" | .200" | .300" | .400" | .500" | .600" | .700"
---------+--------+--------+--------+--------+--------+--------+--------
Stk int | | | | | | |
stk ex | 91% | 85% | 80% | 81% | 74% | 79% |
---------+--------+--------+--------+--------+--------+--------+--------
stk int | | | | | | |
prtd ex | 125% | 96% | 88% | 99% | 92% | |
---------+--------+--------+--------+--------+--------+--------+--------
prtd int | | | | | | |
stk ex | 70% | 74% | 71% | 65% | 63% | 64% |
---------+--------+--------+--------+--------+--------+--------+--------
prtd int | | | | | | |
prtd ex | 96% | 84% | 77% | 80% | 79% | |
---------+--------+--------+--------+--------+--------+--------+--------
Notes:
Neither the intake or exhaust ports on the head flowed were given
a valvejob. The valvejob is the stock one-angle 45' issue from
Ford. In light of the flow numbers gained at lower lifts compared
to a similarly done (1.94/1.60) GT40 iron head with a 3 angle valvejob,
it would seem this head would have greatly benefitted from one.
The GT40 alum heads have a .100" rasied intake port and share a
basically similar exhaust port to a GT40 iron head. After porting
the GT40 iron and alum heads both have nearly identical port shapes
and therefore the flow numbers from either should be comparable
with equal valve sizing, valves and valvejobs.
The stock intake port has a drastically cut-off short turn radius on the
intake port. This seems to lead to turbulence that saps the port's
effectiveness at higher lifts. The bowl area also benefits greatly
from an opened up and radiused seat insert (to remove some bumps).
Thus the intake was given a generous radius where previously it
had only a rather sharp change in direction from horizontal to vertical
in the part of the airflow. The thought is that there are two
ways the intake port could be reshaped:
First was to put a traditionally generous radius on short side
turn and allow the air to follow the short side of the port around
the near side of the intake valve. This was done to the test head above.
The Second method would be to drop the port floor as it approaches
the valvejob area and let the air drop with it and blow across the
intake valve backside rather the follow the short turn of the port
and flow around the near side of the valve. The GT40 iron uses
this method to good effect, and it would have required more material
taken from the alum head and wasn't tried in the test head because the
location of the waterjacket was not known. The risk would be that
if the second method was used, the head may not have enough material
for the port to be dropped without the head cracking in use.
The exhaust port has a very good basic shape and needs some bowl
widening and opening up of the seat insert's limiting area in the
throat area. The exhaust port also has need for raising the roof
of the port near the manifold exit. The area over the thermactor
tube drilled the length of the head is thin, so raising the roof
must be a careful task here.
Also the exhaust port manifold bolt holes are raised somewhat
over a stock location. But not not enough to cause any concern
for header alignment.
The Combustion chamber was only given a few quick brushes with
the die grinder to remove some sharp edged bumps on the area
of the chamber opposite the spark plug hole.
The chamber also seemed to suggest that the intake valve was a
little shrouded at mid lifts (.300"-.400") from the patterns left on
it from previous running time in stock form on a 5.0. So this may
yield a few more cfm if the chamber is pushed back a little bit
with the die-grinder, but it also may not as the intake port
short turn was modified enough that the airflow may not behave
in such a way after the porting to need metal removal from the chamber
area. In all, less than 1/2cc was removed from the comb cham during
it's clean-up.
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