diyPorting.com Part IV Project E7
Exhaust Port

Sneak Preview


Here is a sneak preview of Part IV of Project E7. This page is currently under construction. But you can watch as long as you keep a safe distance. Until I put together the entire article, you may pour over the flow test raw data results I have so far so that you can at least get an idea of areas you may want to avoid when working the E7 exhaust port. There are some surprising results, and I am going to cut another port to verify these results.

None of these procedures are being recommended. The dimensions given in the following procedures are what I achieved on this particular casting. You should not assume that any dimensions listed in the following procedures can be repeated without structural failure. Not all procedures improved flow.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
.1" 41 41 41 42 42 42 42 42 42 42 42 42 41 42 42 42 42 42 43 42 45 46 48 49 51 50 50
.2" 77 76 78 78 80 78 80 82 79 80 79 79 79 79 79 80 80 80 80 81 83 85 86 87 89 90 89
.3" 106 105 111 112 111 115 113 114 113 114 112 114 112 112 114 113 115 114 115 115 115 117 118 122 121 120 120
.4" 113 111 124 125 127 127 133 134 131 133 136 133 136 138 141 140 146 145 142 143 142 143 143 143 144 145 142
.5" 116 113 131 130 134 134 137 136 134 139 138 137 136 142 146 145 154 152 150 147 146 146 147 147 148 149 147
AUC 45.3 44.6 48.5 48.7 49.4 49.6 50.5 50.8 49.9 50.8 50.7 50.5 50.4 51.3 52.2 52.0 53.7 53.3 53 52.8 53.1 53.7 54.2 54.8 55.3 55.4 54.8
CFMs Calculated to 28" H2O





[1] Stock port and stock valve


[2] Removed thermactor flush with roof


[3] Smoothed short side radius


[4] Trimmed outboard side of valve guide


[5] Trimmed inboard side of valve guide. Notice how my carbide burr kept slipping into the bore of the valve guide. I did this on purpose, you see, to illustrate what not to do :(


[6] Trimmed more from inboard side of guide


[7] Cut material from outboard wall of valve pocket


[8] Cut material from outboard wall to exit
[9] Removed thermactor plumbing bulge on roof near exit


[10] Cut deeper into roof between pocket wall and guide on outboard side


[11] Cut even deeper between pocket wall and guide on outboard side
[12] Widen exit ~.050" on outboard wall, top half only.
[13] Widen exit ~.050" on top half inboard wall. Exit now 1.100" wide at top.


[14] Straighten inboard valve pocket wall.


[15] Blend inboard pocket wall to exit.
[16] Further straightening inboard pocket wall
[17] Form more continuous radius on short side radius
[18] Lay short side radius back a bit


[19] Widen short side radius by moving inboard pocket wall back a bit


[20] Square off the rounded corner of the exit, to match others.


[21] Apply 30 degree back cut to valve, .030" wide.
[22] .040" back cut.
[23] .050" back cut.
[24] .060" back cut.
[25] Apply radius to valve head
[26] Apply 15 degree back cut on top of 30 degree cut, .015" wide.
[27] Remove material from valve pocket back wall.


A Happy Port




Notes of Interest

At this point, I would like to admit, these exhaust ports are very sensitve to anything you do to them. Just the opposite of what I always thought. I always figured that the exhaust port was pretty much a "bigger is better" type of deal. The trick was just to keep the Intake to Exhaust ratio in the proper range for your application. But with the work I have done so far, I now realize that the exhaust port is quite a challange. And far more unforgiving as the intake ports. I guess it is because of their smaller size.

The short side radius can make or break your exhaust port. It is very sensitive to the radius applied to it. The best radius seemed to be as round as possible while maintaining a steep drop from floor to valve seat.

Back cut valves seem to respond well with some low lift flow, and they are not as sensitive as intake valves. I stopped the 30 degree back cut at .060" width because it was cutting into the seat angle.

The inboard pocket wall appears to be a good place to pick up some numbers, by straightening the transition between the pocket and runner.

Just about anything I did to the roof near the exit flange hurt flow (2, 9, 12, 13, 20). I removed the thermactor plumbing from another port and got almost the same results. I have a feeling that Ford engineered the thermactor plumbing to work 'with' the E7 exhaust port. I'll have more info on this in the final draft.

The exit was widened to 1.10" at the top half of the port only (above the bolt holes). The roof was not raised, nor the floor lowered.

Exhaust Port Update
 I have cut another exhaust port, and still, according to my flow tests, I certainly cannot recommend raising the roof. With the way I ported this last exhaust port, I lost 4 - 5 cfm when I tried raising the roof about .050". Removing the thermactor boss did raise the high lift numbers about 1 -2 cfm, after porting, but then leveling the lateral roll near the exit roof, lowered them again a couple CFM.

Interesting, I did find a few cfm at .5" by decreasing the radius of the 2 lower corners at the exit!


More good stuff!