906 head porting Dart short turn

[femtnmax]

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.


[/FONT]

 

[RustyRatRod]

I know in Don Dulmage's book he says to leave the short sides and guides slam alone. Says the flow bench "doesn't know the difference. All he says to do is open the bowls up and blend them good and gasket match the intake and exhaust ports but not to go too far in. Kinda makes you rethink some of this other stuff. Comin from an old guy that runs 11.50s in a 4100 pound 74 Charger that speaks volumes.

 

[femtnmax]

I know in Don Dulmage's book he says to leave the short sides and guides slam alone. Says the flow bench "doesn't know the difference. All he says to do is open the bowls up and blend them good and gasket match the intake and exhaust ports but not to go too far in. Kinda makes you rethink some of this other stuff. Comin from an old guy that runs 11.50s in a 4100 pound 74 Charger that speaks volumes.

Thanks for the comparison. Its Good info...Mopar said the same thing...dont touch the short turn. Yet those that reach out quickly found that working the short turn really helped flow. All the references I listed found cfm improvement working the short turn, and doing so got past the flow stall at mid-upper lifts. I notice the short side and bowl volumes of Stealth, and Edy heads is nothing like the oem 906....so there must have been room for improvement.

Technology never stops. This is the age of wet & dry flowbench studies. Anyone telling me that a cylinder head design from the 1960’s only needs a bowl blend to optimize the flow…well they can believe what they want.
But for me…I’ll listen to the likes of Dwayne Porter and Dart wet flow results.

 

[nitrojunkee]

Just wondering how much exactly did you increase the cross sectional area of the port?

 

[ssba]

I hope this doesn't come off sounding too much like a stupid question but, what is the application these ported 906s going to be bolted on? Would they be a high compression
race engine? Large cubic inch stroked engine? Or just general high performance street engine? Or would they work well on any big block standard port build? I suppose I am asking is there a level when you should buy aftermarket? Leaving max wedge ports out of discussion.
I have been torn for years about weather to invest in iron heads I already have or buy aluminum.

 

[femtnmax]

Just wondering how much exactly did you increase the cross sectional area of the port?

The pushrod pinch is the limiting cross section, and was widened only enough to clean up casting errors. The pinch height did not change, and the finished width is slightly less than oem Eddy heads. So very little change to the cross section area. I was trying to keep the limiting port velocity UP. The bowl area was increased, but only to that equal to Mopar templates...research said a 75 degree bowl cut (what I did) removes the same material as the templates.

ssba:
The engine is street performance, a 383/432 stroker going in an Ebody. There are several really good engine builds on this forum....IQ52 has listed several, and Chally340 also. In every case improvements in cylinder head flow translated to increased engine TQ & HP.
MRL performance had a good comment...you can either increase compression or cylinder head port flow to gain TQ/Hp, or DO BOTH and really gain.
So I'm going for the increased port flow, and moderate compression... for a "general high performance street engine".
Would they work well on any big block standard port build? I think so; MRL has it right. IQ52 listed his 'pops' engine build in this form (big block Abody)...very impressive LOW compression engine.

These 906 open chamber heads really limit the compression ratio for pump gas...both static and dynamic, because of the risk of detonation if you go too high on either ratio without the correct camshaft choice and near perfect tuning.
My build will be 9.8 static and 8.0 dynamic. You could go higher on both with a good quench style cylinder head such as the Stealth or Eddy RPM.

This stroker build I'm doing with flat top pistons at zero deck will work with either iron or aluminum heads...just have to do your homework on the static and dynamic compression ratio. The alum heads would require reducing the combustion chamber cc's to make the best ratios...milling the heads is no big deal, just needs to be done the right amount, and pick the correct cam (intake valve closing angle).

I stayed with the iron to be more street friendly at my 5200 ft elevation. Even in the summer the morning temps can drop to near freezing and without a heated intake manifold there are times where the engine can barely pull the car down the road. I had switched my old work truck to all the alum parts...and ended up going back to all oem iron...it runs so much better all day every day. So I'm going the same route with this engine build.
I'm an ASE certified mechanic, have been since 1978. I just like to work on cars. So the idea of studying cylinder head porting and doing the work myself is part of what I like to do.
I have just under $1000 into these old iron heads, with all new parts, and hard exhaust valve seats. Most folks would say its a waste of money. So unless it fills a personal requirement (like my cold summer days), I would really suggest aluminum heads if it is in your budget, mainly for the quench benefits AND the nice out of the box port flow. If I really did my port work correctly I MAY be close to the OOTB flow of the alum heads I suggested.
A bowl cleanup on either of the alum heads would up their performance that much more. Some have room for unshrouding the valves in the combustion chamber too for yet another gain. JMHO.

On the other hand...I used to have a 68 GTX with factory 440 4spd dana60 with 4.10 gears, ALL stock. It ran really strong, won many street races, even against the big motorcycles of the time. It had iron heads and ran great. The body twisting was enough that the windshield was cracking apart more and more every day. I suppose it wouldnt run with todays big strokers, but so what if you don't need it.

 

[jos51700]

I don't know much about about porting, but I know the D-port harley heads flowed like crazy and they have extra material in the floor....So I don't think I'll touch the floor on the next set I port.

 

[femtnmax]

I don't know much about about porting, but I know the D-port harley heads flowed like crazy and they have extra material in the floor....So I don't think I'll touch the floor on the next set I port.

I totally agree. On the 906 heads I was only correcting the too-tall factory short turn height. I'm sure harley has done their design homework over the last 30 years. As I say...technology continues to improve. Look at the new Mopar hemi. The port shapes are so much better than the 60's.

 

[nitrojunkee]

Gotcha. I only ask because I just finished porting a pair of RPM heads. And I chose to open up the pushrod pinch cross sectional area, by quite a bit. I did a fair amount of bowl work as well. I should have flow bench numbers within the next week or two. I can't wait to see what my work yields.

 

[femtnmax]

Gotcha. I only ask because I just finished porting a pair of RPM heads. And I chose to open up the pushrod pinch cross sectional area, by quite a bit. I did a fair amount of bowl work as well. I should have flow bench numbers within the next week or two. I can't wait to see what my work yields.

Sounds great. Could you post your flow numbers?
Who in Colorado did the flow testing? It would be nice to flow my old heads, but getting the heads to the bench is the $$ part.

On the small block mopars, I was able to unshrould the valves alot, which will help flow; had to cut the heads .01 inch to get the chamber cc's back to what I needed. Was there any room to unshrould the valves on your Edy heads?

 

[nitrojunkee]

Sounds great. Could you post your flow numbers?
Who in Colorado did the flow testing? It would be nice to flow my old heads, but getting the heads to the bench is the $$ part.

On the small block mopars, I was able to unshrould the valves alot, which will help flow; had to cut the heads .01 inch to get the chamber cc's back to what I needed. Was there any room to unshrould the valves on your Edy heads?

I'll definitely post the flow numbers when I update my build thread, in the forced induction section. I can put them here too, if you want. Pete at Ridge Reamer is doing the flow bench testing. He does his testing at 25" as opposed to 28". But I'll post both flow numbers at 25" and 28".

There was a small amount of unshrouding I did to the valves, but not much.