RESULTS
So, what is all this time and effort worth? Well, on our 289
heads with stock (1.78"/1.45") valves, we saw the
greatest gains on the exhaust side. Up an average of 20 cfm
below .400, and over 35 cfm at .500. On the intake side the
gains were substantial up to .400" lift, but after that
the stock intake valve really showed its shortcomings. Also
contributing to the less than expected gains was the fact
that I gasket matched to the smaller stock intake gasket,
rather than the Fel Pro 1250.
The home ported 351 Windsor heads, with stock 1.84"/1.54"
valves, showed impressive gains. Some of this is surely due
to this being the second set of heads I ported. The exhaust
side improved by 20cfm at low lifts, and over 40 cfm at .500"
and .600" lift. With a 1.60" exhaust valve, flow
took off, with a whopping gain of nearly 60 cfm (181cfm total)
at .600" lift! That is better than the Edelbrock
RPM head, and within 5% of nearly all other aftermarket
heads! (See our head
flow article.)
The ported 351's using the stock intake valve sizes gained
a max of 23 cfm at .400" lift, but with 1.94" intake
valves, peak flow increased to 211cfm at .500", just
a couple shy of the Edelbrock head. Not bad for a low-buck
effort!
One of the things we learned here is the limitation of the
stock valve sizes. It is clear that the 1.78"/1.45"
valves are quite restrictive. With a stock cam, lifts below
.450", you can get away with the stock valve sizes, but
if you plan to run a healthy cam, you should really consider
going up in valve size on the stock 289/302/5.0 heads. The
Chevy (1.94"/1.60") replacements are inexpensive and will
get the intake flow on a ported head to above the 200cfm mark.
CONSISTENCY
When you purchase a set of aftermarket heads, you expect
all of the respective intake and exhaust ports to flow identical
to one another. This of course is achieved with very precise
machinery and manufacturing processes. However when you port
your own heads, you really don't have any assurance, other
than your own eyes and fingers, that your ports are identical
to each other. Is this something to be concerned about? We
don't think so. Assuming you didn't radically change your
porting habits as you went from port to port, common sense
would dictate that your ports are fairly consistent. Check
them over good when you are done, use a set of calipers to
measure the port openings, and correct any obvious differences.
If you had access to a flow bench you could flow each port
and make adjustments are necessary, but chances are you don't
have this luxury.
Hopefully this guide has inspired you to port your stock iron
heads, before dropping big bucks on a set of aftermarket heads.
Don't get us wrong, aftermarket heads are great, but we feel
that everybody should try their hand at porting. There is
truly no better feeling than that of horsepower that you created
yourself, for next to nothing.
If you have questions or tips to add, feel free to post them
in the Home
Porting Forum. 
FLOW NUMBERS: 289 Head |
INTAKE
|
|
Stock
289 |
Ported
289 |
GAIN |
.100 |
44 |
56 |
+12 |
.200 |
90 |
112 |
+22 |
.300 |
131 |
148 |
+18 |
.400 |
152 |
167 |
+15 |
.500 |
168 |
174 |
+6 |
.600 |
164 |
177 |
+13 |
|
EXHAUST
|
|
Stock
289 |
Ported
289 |
GAIN |
.100 |
39 |
42 |
+3 |
.200 |
70 |
83 |
+13 |
.300 |
92 |
115 |
+23 |
.400 |
109 |
139 |
+30 |
.500 |
118 |
153 |
+35 |
.600 |
122 |
163 |
+41 |
|
Stock
5.0
|
|
INT |
EXH |
.100 |
48 |
41 |
.200 |
92 |
78 |
.300 |
130 |
95 |
.400 |
141 |
102 |
.500 |
155 |
106 |
.600 |
158 |
105 |
|
FLOW
NUMBERS: 351W Head |
INTAKE
|
|
Stock
351W |
Ported
351 - Stock Valves |
GAIN |
Ported
351 - Chevy Valves |
GAIN |
.100 |
50 |
58 |
+8 |
57 |
+7 |
.200 |
101 |
115 |
+14 |
114 |
+13 |
.300 |
144 |
156 |
+12 |
165 |
+21 |
.400 |
167 |
190 |
+23 |
198 |
+31 |
.500 |
179 |
192 |
+13 |
211 |
+32 |
.600 |
180 |
<192 |
+12 |
211 |
+31 |
|
EXHAUST
|
|
Stock
351W |
Ported
351 - Stock Valves |
GAIN |
Ported
351 - Chevy Valves |
GAIN |
.100 |
45 |
57 |
+12 |
47 |
+2 |
.200 |
75 |
97 |
+12 |
93 |
+18 |
.300 |
101 |
125 |
+24 |
132 |
+31 |
.400 |
110 |
145 |
+35 |
162 |
+52 |
.500 |
118 |
159 |
+41 |
177 |
+59 |
.600 |
122 |
168 |
+46 |
181 |
+59 |
|
To
view these charts in graphical form, see our Head
Flow guide. |
All
flow numbers are at 28" H20, flowed on a Superflow
600 bench.To simulate actual transitions, the intake side
was fitted with a clay lip, and the exhaust port was fitted
with a 1 7/8" diameter pipe, approx. 4" long with a 90
deg. bend. The bore size used was 4.030". The end chamber
was tested on each head. |
|