906 head porting Dart short turn

Home ported the 906 heads. For info as to what worked and what to look out for I used the following websites:
Part 1, big block heads
http://www.moparmusclemagazine.com/techarticles/5115_cylinder_heads/
Part 2, big block heads
http://www.moparmusclemagazine.com/techarticles/5118_cylinder_heads_ii/
Part 3, big block heads
http://www.moparmusclemagazine.com/techarticles/5120_cylinder_heads_iii/
Stage V Fast68
http://www.moparts.org/Tech/Archive/bb/55.html
stage V head porting
http://www.moparmusclemagazine.com/howto/mopp_0106_how_to_install_ported_stage_v_heads/

For the intake port short turn shape there was only very general info, such as “short turn too tall” and “laid back short turn”.
While looking for more ideas I compared the 906 intake port floor/short turn shape to Dart 200cc and 230cc Iron Eagle heads. I did not measure the 906 intake port volume, but research suggested a volume of 180-200cc, so similar to the smaller Dart. The two Dart heads had similar short turn height, which was a little less than the 906 port. On the two Dart heads the amount of short turn ‘lay back’ from the peak of the short turn to the valve seat cuts was nearly identical. Both Dart heads had much larger bowl areas than the 906, so they are slowing the flow down more after going over a ‘tall’ short turn. So I followed the internet sites and the Dart floor shape to arrive at a final port shape. I made a template of floor/short turn and used it as a guide while shaping the intake port floor.

The first pic is templates made for the Dart 230cc port short turn/floor, and the 906 floor, with the dark wire showing the 906 original port floor shape. I did not lay back the 906 short turn quite as much as the Dart. I did not want to hit water. The bottom of each template is the cylinder head deck surface. The notch at left end of template curve is the intake manifold gasket.

Second pic is OEM chamber view for reference. Intake valve is oem 2.08 diameter, the 75 degree throat cut is in there; along with hard exhaust seat for 1.81 valve.

Third pic is chamber view ported.
Unshrouded the valves up to near the head gasket, taking into account where the engine block cylinder met the cylinder head combustion chamber. There was not much blending that could be done without having the combustion chamber larger than the block cylinder.
Blended the spark plug boss for smooth crosswise flow from intake valve, and blended the edges of cup at base of spark plug hole, between plug hole and valve seat area. Plug blend is said to be worth up to 5 cfm.
For detonation prevention smoothed combustion chamber flat area opposite spark plug, and blended this area up to the head gasket surface. Left the rest of chamber rough to promote fuel atomization.
I left a anti-reversion step in the intake port bowl close to exhaust port. This is to help reduce exhaust flow up/into intake port during intake/exhaust valve overlap.

fourth pic is exhaust port bowl
Blended the hard exhaust seat into the port bowl. Shortened the guide height .125 inch to enlarge the port cross section area. Flattened the bump on the port roof out near the port exit. Blended the short turn from the exhaust seat to port exit. Widened port wall starting just past guide on cylinder center side of exh port, and widened and blended the wall on cylinder-wall side of exh port, and blended this back to behind the smoothed guide boss.

[FONT=&quot]fifth pic is exhaust port outlet
Did not enlarge port exit at all. Blended all port shaping stopping just short of port exit.

sixth pic is intake bowl
Removed the original long guide boss back to near the guide boss hole, leaving a slight hump of the original guide boss along port roof from near its beginning at intake manifold to avoid punching thru the thin casting near the valve spring.
Widened the port roof on each side of guide boss by removing material from the guide boss, very little removed from port wall opposite the boss…again to avoid punching thru the port wall. The final narrow side of port roof (cylinder centerline side) is nearly as wide as the OEM ‘wide’ side (cylinder wall side).
Left the port walls rough with 60 grit finish to promote fuel air mixing. Liquid fuel will separate from the airflow and stick to smooth surfaces, so I left the intake port surfaces rough.
Anti reversion step is a remainder of the 75 degree throat cut. Left this where intake port comes up along side the exhaust seat. The 75* cut removes the same material as using the Mopar templates. Intake port throat diameter is 89% of valve diameter, to go with .530 valve lift.
Was careful to not completely blend the depression in the bowl at lower left of photo where cylinder center wall blends into bowl. They said you will punch thru the port if this 'dent' is blended out.

Seventh pic is intake port short turn
To follow the general idea of the Dart 230cc short turn shape, the highest point of the 906 head short turn was lowered .05 inch with a cut right at the center of the port, using mechanics wire to verify the cut depth. Then blended & widened this cut out to each side across entire short turn apex. By the time the cut was finished and blended to the seat lay-back cut the height of the short turn had been reduced by .10 inch. To start the lay-back cut which will be between the short turn peak and valve seat, made a felt tip line parallel to valve seat located .2 inches up the port from the edge of the 75 degree throat cut, and made a carbide cut in the center of the port .05 inch deep with this cut blending to nothing when it reached the felt tip line. Blended this cut to each side following the arc of the valve seat. Then blended this cut into the previous cut at the peak of the short turn. New lower short turn height was blended upstream just over half way to port entrance at intake manifold gasket surface.
Compared to the OEM short turn, the finished shape was .1 inch lower height, and .1 inch laid back at a location half way between oem peak of turn and 75 deg cut/valve seat.

Last pic is intake port pair
Removed some of the head bolt bump on cylinder wall side of port. Used my home-made E-tool to leave .20 inch of material at this location.
Widened the pushrod pinch only enough to clean up casting errors. Port entrance was measured to and squared up to Edelbrock DP4B intake manifold ports.


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