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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.


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