NHRA Horsepower Ratings for the 273

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69 Cuda 440

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273/275 D Dart

The 1966 273/275 HP is still rated at that HP factor.

Though suprisingly the NHRA lists the D Dart as being available in the
both the GT and convertible (which it wasn't).

And they factor the D Dart as a Super Stock only car. Yet, in 1966
the car was specifically built for D/Stock (10.60-11.29 Wt/Hp), and as
a 4-Speed Manual-only application.

Back in 1966, Dodge labeled the D Dart Package as a +40 HP Package
over the standard 273/235 HP 'Commando'.

The Doug Headers (placed in the trunk compartment of the D Darts) were
not part of the +40 HP increase.

It was strictly the Camcraft Camshaft, Racer Brown Valve-Springs,
Free-Flowing cast-iron intake manfold, Holley carburetor and factory
modified dual-point distributor (mechanically advanced).

The Weber Clutch assembly was obviously not a factor in the Horsepower
increase.
 
R/T,

Here is the information you wanted.

Camcraft Camshaft .495/.505 Lift - 284* Duration - 60* Overlap

Racer Brown #VR-18X Valve Springs - #313 lbs. @ 1.05" (Open) and #150 lbs. @ 1.55" (Closed)

Cast Iron Intake Manifold - Throttle bore openings opened up to 1 11/16"

Aluminum-plate carburetor adaptor.

Holley Model #4160 / List #3778 - 700 CFM Carburetor (Factory Modified)
(1 11/16" Primary / 1 11/16" Secondary) - (Venturies 1 5/16" x 1 3/8")

Dual-Point Distributor, w/Vacuum advanced removed, and pre-set to 35* Total Advanced
 
Mike,

The 273/235 HP was lowered to 220 HP, then lowered again.

Now it is rated at 210 HP.

I would have to agree, Mopar did overate the 273 Commando.

A 2940 lb. A-Body should have had a Wt/Hp Factor of 14.00 with a 210 HP rating.

Those cars would have done a lot of damage back in the mid-late 60's and
early-70's in the NHRA Class (14.00 - 14.99 Wt/Hp).
 
Mike,

In 1965 thru 1967, Mopar should have offered the 273 in both a 210 HP and 235 HP version.

The original 235 HP 'High Performance' was overated by 25 HP.

Yes 10.5-1 Compression ratio pistons, but the solid lifter camshaft and small
carburetor limited it's performance.

The Carter AFB (500 CFM) and low-plane 'X-design' cast iron intake worked
well in the low and mid-range levels, but not on top-end.
 
69 Cuda 440 said:
Mike,

In 1965 thru 1967, Mopar should have offered the 273 in both a 210 HP and 235 HP version.

The original 235 HP 'High Performance' was overated by 25 HP.

Yes 10.5-1 Compression ratio pistons, but the solid lifter camshaft and small
carburetor limited it's performance.

The Carter AFB (500 CFM) and low-plane 'X-design' cast iron intake worked
well in the low and mid-range levels, but not on top-end.
Click to expand...

The 2 barrel engine was rated at 180 hp. The 4 barrel was 235 but it would be interesting to know how true those numbers were. I'll bet they didn't dyno them back then. tmm
 
Tool Man Mike,

We ran a 273/235 HP Commando back in 1967, with a 67' Barracuda Fastback.
And ran it from 1967 thru 1971 in Stock Class.

Since we bought the car 'practically new' in 100% stock trim, we had a chance to
have it tested on a 'new' Bear Dyno Machine.

I can't remember the exact numbers, but it was not near 235 HP @ 5200 RPM
'at maximum level'.

Carter AFB Carburetor = 1 7/16" Primary - 1 9/16" Secondary
Venturies = 1 1/16" Primary - 1 1/4" Secondary

CFM Rating = 500

Camshaft = .415 Intake / .425 Exhaust - 248* / 248 * Duration - 26* Overlap

Valve Spring Pressure = 210 lbs. (w/valve open)

Cylinder Heads = 1.78" Intake / 1.50" Exhaust

Port Size - Intake = 1.70 square inch / Exhaust = 1.25 square inch
 
I wish I would have spent the money to have mine dyno'd when I built it.
 
Valve Spring information has always been a bit jaded.

The 273 2-Barrel (Camshaft Lift .400 / .411) w/.020 Lash

Valve Springs
83 lbs. @ 1.69" (Valve Closed)
177 lbs. @ 1.31" (Valve Open)
-----------------------------------------------------------

The 273 4-Barrel' Commando (Camshaft Lift .415 / .425) w/.0.20 Lash

98 lbs. @ 1.69" (Valve Closed)
210 lbs. @ 1.295" (Valve Open)
 
I think if you do the math you'll find that the 235hp 273 was actually at 11 1/2 to 1 CR
 
Dart 4 Forte,

If you mill the cylinder heads, and a get to 57.3 CC, and the deck block is
trued with a piston height of .129", the compression ratio should be in the range of 10.5 to 10.8

As for the stock 273/235 HP valve springs, they had a thicker coil than the 273/180 HP 2-barrel engine.

We found that out the hard way.............
 
69 Cuda 440 said:
Dart 4 Forte,

If you mill the cylinder heads, and a get to 57.3 CC, and the deck block is
trued, the compression ratio should be in the range of 12.0 to 1.

As for the stock 273/235 HP valve springs, they had a thicker coil than the 273/180 HP 2-barrel engine.
Click to expand...

I just sat down with the guy that builds my motors and using the actual specs of the motor stock from the factory to include the stock steel shim gasket and the domed piston you get a little over 12.2 to 1. The 2 barrel motor using the stock specs the motot CR comes in slightly over 9.2 to 1.

The actual formula can be found in the NHRA rule book.
 
69 Cuda 440 said:
Tool Man Mike,

We ran a 273/235 HP Commando back in 1967, with a 67' Barracuda Fastback.
And ran it from 1967 thru 1971 in Stock Class.

Since we bought the car 'practically new' in 100% stock trim, we had a chance to
have it tested on a 'new' Bear Dyno Machine.

I can't remember the exact numbers, but it was not near 235 HP @ 5200 RPM
'at maximum level'.
Click to expand...

I'm assuming this was an engine dyno, not a chassis dyno, correct? I'd love to see a HP/torque chart just to see at what point these engines started "falling off". I always thought with the 4-barrel carb, open plenum intake, solid lifters and the dual point, they'd be good for over 6500 easy, if not 7000.
 
Actually both,,,,,

It was Engine Dyno'd

Then, the Bear Dyno

The stock 273/235 HP, valves floated out at just over 5200 RPM.

In 1967, we ran it in F/Stock (12.50 - 13.99 Wt/Hp). Completely stock,
4-Speed with 3.23 Sure-Grip Posi.

Just barely got into 4th Gear at the Traps.

Best E.T. = 16.16
Best MPH = (I have to look up the old paperwork)
 
Matt,

The 273/180 HP is now down to 162 HP

The 273/235 HP is now down to 210 HP

Where was the NHRA they 40+ years ago.
 
i had a 65 formula s 4 speed 3.91s weighd 3,125 ran consistant 14.7s in the late 1960s. was J amature clase record holder 14,81 at my track for a year with the stock 3.23s. blew that rear end. lots of fun
 
69 Cuda 440 said:
Actually both,,,,,

It was Engine Dyno'd

Then, the Bear Dyno

The stock 273/235 HP, valves floated out at just over 5200 RPM.
Click to expand...

That's....kind of unbelievable and sad. If those engines had extra stout valve springs, what did the 273 2-barrel valves float at?? Good lord, I had a '72 Pontiac 350 that revved clean to about 5700 RPM back in the day.....and it had 75,000 mi on it and was originally a 2-barrel engine stock.
 
273 Engines

273/180 HP
180 HP @ 4200 RPM

273/235 HP
235 HP @ 5200 RPM

273/275 HP ( Dart)
275 HP @ 6000 RPM

Our stock 1967 273/235 HP Barracuda Fastback, 4-Speed, w/3.23 Posi ran a best
of 16.16 in 1967 classed in F/Stock = (12.50 - 13.99 Wt/Hp)

In 1968, was classed in J/Stock = (12.50-12.99 Wt/Hp)
Hooker Fenderwell Headers, 4.56 Gears, Hurst Shifter, Sun Tachometer,
Stewart-Warner Electric Fuel Pump, Distributor Modification.
Suspension Traction Pinion-Snubber, and 7" Wide-Slicks.

(With no modifications done to the engine)

14.70's @ 96 MPH
 
1965 Plymouth factory report.

Their 1965 Plymouth Barracuda, 273/235 HP Commando with factory Hurst 4-Speed shifter, low-restriction/high-flow exhaust muffler and 3.91 Gears (7 1/4" Rear).

15.56 @ 88 MPH.

Red-Line 6000 RPM's.
 
69 Cuda 440 said:
Actually both,,,,,

It was Engine Dyno'd

Then, the Bear Dyno

The stock 273/235 HP, valves floated out at just over 5200 RPM.

In 1967, we ran it in F/Stock (12.50 - 13.99 Wt/Hp). Completely stock,
4-Speed with 3.23 Sure-Grip Posi.

Just barely got into 4th Gear at the Traps.

Best E.T. = 16.16
Best MPH = (I have to look up the old paperwork)
Click to expand...
ouch.
Might as well use a sundial to time it lol.
 
Well,

We did have the spare tire and the jack assembly still in the trunk.........

Worth about .05 off the E.T.

Those 6.94 x 14" spare tires were heavy..............LOL
 
Wow, this just blows me away. You always hear that Mopar "under-rated" their engines... Obviously not the case here.
 
The two main problems with the 273 in my opinion are related to the fact that it has a small bore, that makes compression harder to acheive, it takes a dome piston to get anywhere near the 11 to 1 range, and a small bore shrouds the valves and reduces the airflow potental.. Also a dome piston is said to hamper flame travel compared to a flattop, but I dont really know how much that effects power output.
 
Rocky65 said:
Wow, this just blows me away. You always hear that Mopar "under-rated" their engines... Obviously not the case here.
Click to expand...

273/235 HP was re-factored by the NHRA down to 220 HP in 1976, then
got another adjustment down to 210 HP.

They were correct.

Other over-rated engine combinations.
1964/1965..........426/365 HP (Street Wedge)
1963 thru 1965....383/330 HP
1966/1967..........383/325 HP
1968 thru 1970....383/330 and 335 HP
1967 thru 1970....440/375 HP

The 1966 Dodge D-Dart 273/275 HP, was paper horsepower.
 
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