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273 COMMANDO
The 273 Commando was available two ways in '66. The
standard 235 HP version and a D/Stock version rated at 275 HP.
The D/Stock version was available as both a limited production
factory option, and an over-the-counter dealer option in '66.
The option was intended to help the A body Mopars to compete in
the D/Stock class with an advertised LBS/HP ratio range of 10.6
to 11.29. The option, which was offered from the factory without
warranty, included a Holley 4160 carb, adapter plat, a 284 degree
.495" I/ .505" E lift cam and spring set, tuned headers dumping
into the stock exhaust, and, in the "D/Dart tested by Car Craft
in August of '66, a 4.86:1 8-3/4" sure grip 3rd member. As Car
Craft notes:
Straight "out of the box" so to
speak, the D/Dart turned 94.21
mph in 14.33 seconds which was
almost as fast as the street hemi,
our test car of a few months back.
The engine still had less than 150
miles on it...
I have also seen references to the under rating by the factory
of the 273 Commando's output (people have equated it with the
"K" code 289 Ford at 271 HP), and I won't disagree with that.
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| ITEM | SPECIFICATION |
| Carburetor: | 600 CFM AFB / Holley 4160 (D/Stock) |
| Bore: | 3.625" |
| Stroke: | 3.31" |
| Compression Ratio: | 10.5:1 |
| Cam: |
| Lift | Duration |
| Intake | Exhaust | Intake | Exhaust |
| Commando: | | 0.425" | 0.425" | 248° | 248° |
| D/Stock: | | 0.495" | 0.505" | 284° | 284° |
|
| Gross Horsepower: | 235 @ 5200 RPM / 275 @ 6000 RPM (D/Stock) |
| Torque: | 280 Ft/Lbs @ 4000 RPM / 295 Ft/Lbs @ 4400 RPM (D/Stock) |
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| Some Hop-Up Ideas for the 273. |
- Aluminum Intake: the stock 273 intakes are heavy and don't
flow all that well. An Edelbrock, Wyand, Ofenhauser, or
MOPAR aluminum intake will save pounds, make more power,
and improve drivability.
One issue for 273s is that the angle and size of the intake
bolts changed for the '66 model year. Later intakes can be
adapted to the '64 and '65 273 by any good machinist or
engine builder. The bolt holes have to be redrilled to
the older angle and the bolt hole openings in the intake
have to be re-spot faced to be normal (90°) to the bolt.
The '64 and '65 intake bolts were 5/16" so you also need to
use hardened washers under the intake bolt heads to take up
the slack in the 3/8" bolt hole openings and maintain the
proper torque on the early 5/16" bolts.
- Cam: I don't recommend a hydraulic cam for the 273. The 273
has mechanical valve gear and requires special shorter
pushrods if you convert it to a hydraulic. Also you get a
better performance bang for the buck with a mechanical cam.
Here are some I like for the 273 Commando roughly in order
of "hotness":
| CAM | Lift I/E | Dur I/E | Dur@0.050" | Lobe_Sep | RPM_Range | Min_Comp |
| Competition Cams 270 S: | 0.468"/0.468" | 270°/270° | 224°/224° | 110° | 1800-5800 | 9:1 |
| Comp Cams 20-233-4 XS268S: | 0.488"/0.501" | 268°/274° | 230°/236° | 110° | | |
| MOPAR Perf MOPP4529346: | 0.490"/0.490" | 276°/276° | 235°/235° | 112° | | |
| Competition Cams 282 S: | 0.495"/0.495" | 282°/282° | 236°/236° | 110° | 3000-6000 | 9.5:1 |
|
Hughes Engines HEV3945AS: | 0.546"/0.560" | 260°/277° | 239°/245° | 107° | 2100-5900 | 9.5:1 |
| Comp Cams 20-230-4 XS274S: | 0.502"/0.511" | 274°/280° | 236°/242° | 110° | | |
| Edelbrock Performer RPM: | 0.488"/0.510" | 308°/318° | 234°/244° | | | |
| Comp Cams 20-231-4 XS282S: | 0.520"/0.540" | 282°/290° | 244°/252° | 110° | | |
|
Hughes Engines HEV4550AS: | 0.560"/0.575" | 277°/283° | 245°/250° | 106° | 2300-6300 | 9.75:1 |
All these cams will require matched valve springs, and the
ones with lift beyond 0.500" would REALLY benefit from
some port work to take advantage of the higher lift they provide.
Also most of these cams require at least 9.5:1 or more static
compression to really work, so if your tuning up a 2 barrel
273, be prepared to do some cylinder head milling. To get to 9.5:1
with flat top pistons you need to mill the 57 CC 273 heads to 52 CC,
assuming a 0.005" deck height and a 0.032" installed head gasket
thickness.
- Ignition: Convert to MOPAR Performance electronic ignition using the
chrome control unit. The standard control unit will work fine
in most cases but the chrome one provides a hotter spark from
idle to 8,000 RPM.
- Carburetor: For the street the stock AFB should be fine up to a point,
but even Chrysler put a Holley on when they got serious. For
auto trans cars use a vaccum secondary 4160, for manuals a 4150
double pumper, no bigger than 650 CFM in both cases. Make sure
your using a dual feed, center hung version of these Holleys or
you'll have some of the same issues under hard cornering, braking,
and acceleration that the AFB has. Holleys DO have a problem with
flooding out under heavy braking here are the fixes (use ALL of
them):
- Use the long "dog whistle" float bowl vent baffles.
- Install jet extensions on the rear (secondary)
metering block.
- Install a piece of fuel line between the bowl vents
so that they are extended vertically an inch or so.
Cut a small section out of the top of the fuel line's
arc and punch a small hole for the air cleaner stud
to pass through (a little insurance against it being
inhaled).
- Here is a more detailed listing of 273 Factory cam
Spec's
Intake Exhaust
======== =======
Std. 273 2 Brl (8.8:1):
Valve Lift: 0.395" 0.395"
Duration: 240ø 240ø
Opens: 14ø BTDC 58ø BBDC
Closes: 46ø ABDC 2ø ATDC
273 Commando (10.5:1):
Valve Lift: 0.425" 0.425"
Duration: 248ø 248ø
Opens: 14ø BTDC 56ø BBDC
Closes: 54ø ABDC 12ø ATDC
D/Stock 273 (10.5:1, Actually a Camcraft part):
Valve Lift: 0.495" 0.505"
Duration: 284ø 284ø
SAE Gross Horsepower & Torque:
Std 273
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180 @ 4200 RPM & 260 Ft/lbs @ 1600 RPM
273 Commando
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235 @ 5200 RPM & 280 Ft/Lbs @ 4000 RPM
D/Stock 273
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275 @ 6000 RPM & 295 Ft/Lbs @ 4400 RPM
- More to come...
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