Commando 273 cam specs

Miranthis said

I have been researching the posts on the Commando 273 cam specs as I rebuild my 66 Commando 273. My engine guy is asking for the "full specs" for the Commando 4 bbl cam including "duration at 0.050". From the stuff below, can I glean all that I need?

From 66fs 's post on another thread:

The Commando cam works very well. We measured an original 67 Commando cam with 50,000 miles on it at Racer Brown's Cam Doctor's Analysis.

Intake:
110.4* center ATDC
202.8* duration at .050 Crank degrees
.405" net valve lift

Exhaust:
110.4* center BTDC
202* duration at .050 Crank degrees
.414" net valve lift

From other net-sources, what the usual "published specs" show is:​

View attachment 1716368777

Click to expand...

Sorry to go on the tangent, but here's what you are looking for...

The 66 Commando 273 cam had 248° duration...








From similar MP cams with 248° duration, you can see that the duration @.050" is 211°







Now, adding the 66 273 4 bbl to my spread sheet, we come out with...




Lift at valve:
Int = .415"
Exh = .425"

Lift at cam: (using 1.5 rocker ratio)
Int = .277
Exh = .283

Advertised duration:
Int = 248°
Exh = 248°

Duration @.050":
Int = 211°
Exh = 211°

Open/Close Advertised:
Int Op = 14°
Int Cl = 54°
Ex Op = 56°
Ex Cl = 12°

Overlap = 26°
Int Centerline = 110°
Exh Centerline = 112°
Lobe separation = 111°

Open/Close @.050":
Int Op = 4.5° ATDC
Int Cl = 35.5° ABDC
Ex Op = 37.5° BBDC
Ex Cl = 6.5° BTDC


***********************************************************************************************************

However I see something odd with those numbers... There may be errors in the service manual numbers or rounding error...

Chrysler likes to have the intake centerline, exhaust centerline, and lobe separation "the same" number... And the intake open/close are mirrors of exhaust open/close...







So, if I correct the intake centerline, exhaust centerline, and lobe separation to all equal 111°, you end up with:

Look at the second row...






Lift at valve:
Int = .415"
Exh = .425"

Lift at cam: (using 1.5 rocker ratio)
Int = .277
Exh = .283

Advertised duration:
Int = 248°
Exh = 248°

Duration @.050":
Int = 211°
Exh = 211°

Open/Close Advertised:
Int Op = 13°
Int Cl = 55°
Ex Op = 55°
Ex Cl = 13°

Overlap = 26°
Int Centerline = 110°
Exh Centerline = 112°
Lobe separation = 111°

Open/Close @.050":
Int Op = 5.5° ATDC
Int Cl = 36.5° ABDC
Ex Op = 36.5° BBDC
Ex Cl = 5.5° BTDC


These numbers mirror each other which is what you typically see with the Chrysler grinds...






However, I just noticed an interesting thing when highlighting the above picture... Notice how all of the non-split pattern HYDRAULIC cams have mirror open/close numbers, but the non-split pattern SOLID cams are not mirror numbers, but slightly offset by a degree or two... Was this on purpose or an error (maybe roundoff error)???

It only effects the open/close numbers by 1° which won't be noticeable on a dyno or seat of the pants, but what is the intended grinds for these cams???
What do you guys think???