The porting work considered here was just basic. We were looking for the biggest gains for the least time-consuming level of rework. Rather than go for the classic sandpapered shine, we sought to just leave the modifications in a smooth carbide-cut finish, and quantify the results of this level of modification with additional flow testing. The first step was to simply blend the machining cuts into the port bowl, a level of work usually referred to as a “bowl blend.” While in the vicinity, a mild reworking of the port short turn was also performed, and the head went right from the porting stand to the flow bench, producing the results seen in the third columns of the flow charts. As can be seen, this level of modification really unlocked a healthy amount of flow, with strong gains everywhere on the flow curve. Testing showed an increase of 35 cfm at peak intake flow, with the exhaust showing a 22 cfm gain.

At this point we could say that the performance character of the heads was radically changed, with flow numbers that would produce a very respectable street performance engine. In keeping with our objectives of maximum improvement for a minimal level of rework, we looked to one more popular modification on the intake side of the port: the port match. The intake port is opened at the manifold side to match the desired gasket size, in this case a standard Fel-Pro 2013 gasket for the small-block Mopar. Potential flow gains from gasket matching will depend upon the architecture of the cylinder heads, and in the case of these particular castings, the narrow and restricted pushrod pinch area is a definite source of restriction. Again, leaving the work in a smooth carbide-finished state, the port entrance was gasket matched, working into the runner to enlarge the pushrod restriction to the practical safe maximum allowed by the existing iron. Back on the flow bench, the port match/pushrod pinch work showed a gain of 14 cfm, leaving no doubt that this area represented a restriction.

So what did we get for our modest cylinder head modification efforts? Looking at the flow curve, the lower lift and midrange numbers really equal some of the better aftermarket cylinder heads in terms of flow. The competition-style valve job is responsible for that result. Since a valve job is going to be a part of any cylinder head rebuild it is worth the effort to find a shop that will do a performance cut. Looking at the peak numbers, the heads deliver flow on par with a good set of entry-level aftermarket heads, and actually exceed the flow of some of the offerings on the market. With an improvement of 50 cfm from just three steps, we consider this to be a very practical level of modification in terms of cost/time versus the improvements. That's enough extra flow to support up to 100 extra horsepower in an all-out race-style engine, and 50 or more in a typical street piece.

Cylinder Head Flow

SuperFlow 600 Flow Bench
Tested at 28-inch depression
Tested at Dr. J's Performance


Lift Stock V-Job Bowl Match
100 51 65 66 67
.200 105 128 135 140
.300 159 170 184 196
.400 187 192 224 234
.450 191 197 229 243
.500 193 195 225 241
.600 188 194 224 229
.700 189 194 223 231


Lift Stock V-Job Bowl
.100 48 60 54
.200 101 106 105
.300 135 134 133
.400 149 152 160
.500 154 159 170
.600 159 161 176
.700 160 163 181

Stock: factory Mopar 587 small-block casting
V-Job: Dr. J's competition 5-angle valve job*
Bowl: blend machining step and short turn
Match: port match and enlarge pushrod restriction**
* machining terminates with large mismatched step into bowl
**port match intake only

Basic Costs

Competition valve job $200
16 valves $128

7. An additional machining step to the valve job is to sweep the chamber with a cutter that is designed to provide a finished top-cut, and move the chamber walls outward to further de-shroud the chambers to the vicinity of the head gasket line.

8. Here is the completed machine work on the intake side. Note the smooth profile running from the chamber, right into the bowl to the end of the machine work. The large stepped-mismatch where the machining ends needs to be blended by hand.

9. The exhaust ports on these heads retain the stock 1.60-inch valve size, but the radius seat-cutter used by Dr. J’s enlarges the throat area below the valve.

10. To improve flow, especially at low lift, the intake valves are back-cut with a 30-degree angle, improving the transition at the back side of the valve.

11. A basic bowl blend will smooth the transition from the bottom cut into the port. We went a step further to gain more flow, lightly blending the short turn on the intake and exhaust ports. The port work was left at a smooth carbide-cut finish, rather than pursue any additional polishing with sanding rolls. Flow was up considerably.

12. Looking for another incremental improvement, the intake side was gasket port matched, and the pushrod restriction was enlarged to give the port more area to breath. This modification is very effective at improving flow with these particular castings.

Dr. J's Performance
436 S Montgomery Street
CA  92868
Racing Engine Valves