273 commando heads vs. standard
- Thread starter smokn440
- Start date
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cavemanmoron
Well-Known Member
As far as I know,
Not really any difference.
I used # 302 heads, which have hardened valve seats,
and have the small combustion chamber,
when I built my 318 to replace my tired 273. ;)
I used a 318 to rebuild while still driving my Valiant to car cruises,
I figured why do a 273, when for the same money I can have a little more power.{I did not want a 340/360, as I don't want to take a chance of
breaking the stock push button tranny, or the 7.25" factory sure grip.}
2465315 273 1964-65 1.78 1.50
2532080 273 1964-65 1.78 1.50
2536178 273 1966 1.78 1.50
2658234 273 1966 1.78 1.50
2658920 273/318 1966-67 1.78 1.50
2843675 273/318 1968-74 1.78 1.50
The 318-2bbl heads (4323302) used from 1985 on are a swirl port design with a closed (heart-shaped) combustion chamber design with a chamber volume of between 56 and 65 cc. The 4 heads I examined averaged 62cc in volume. The 302 head has 1.78"/1.50" valves and small ports averaging 54cc on the exhaust side and 118cc on the intake side. The intake ports have a more severe dogleg than earlier heads because the holes for the pushrods are larger - 11/16". Cars equipped with the 302 head have a dished piston to keep the compression ratio from being too high. Some cars left the factory with nail head exhaust valves in 302 heads, others with semi-tulip exhaust valves, which add 0.6-0.75 cc to the chamber volume. There is an interesting excerpt in "Mopar Engines", page 72, describing how such a head was ported and made to flow as well or better than other small block cylinder heads. Apparently, this experimentation resulted in the master for today's Mopar Performance P4452758 cylinder head
http://mopedia.org/2658920
Not really any difference.
I used # 302 heads, which have hardened valve seats,
and have the small combustion chamber,
when I built my 318 to replace my tired 273. ;)
I used a 318 to rebuild while still driving my Valiant to car cruises,
I figured why do a 273, when for the same money I can have a little more power.{I did not want a 340/360, as I don't want to take a chance of
breaking the stock push button tranny, or the 7.25" factory sure grip.}
2465315 273 1964-65 1.78 1.50
2532080 273 1964-65 1.78 1.50
2536178 273 1966 1.78 1.50
2658234 273 1966 1.78 1.50
2658920 273/318 1966-67 1.78 1.50
2843675 273/318 1968-74 1.78 1.50
The 318-2bbl heads (4323302) used from 1985 on are a swirl port design with a closed (heart-shaped) combustion chamber design with a chamber volume of between 56 and 65 cc. The 4 heads I examined averaged 62cc in volume. The 302 head has 1.78"/1.50" valves and small ports averaging 54cc on the exhaust side and 118cc on the intake side. The intake ports have a more severe dogleg than earlier heads because the holes for the pushrods are larger - 11/16". Cars equipped with the 302 head have a dished piston to keep the compression ratio from being too high. Some cars left the factory with nail head exhaust valves in 302 heads, others with semi-tulip exhaust valves, which add 0.6-0.75 cc to the chamber volume. There is an interesting excerpt in "Mopar Engines", page 72, describing how such a head was ported and made to flow as well or better than other small block cylinder heads. Apparently, this experimentation resulted in the master for today's Mopar Performance P4452758 cylinder head
http://mopedia.org/2658920
moparlee
64 Valiant
Well, like Caveman said, they should be the same. Unless it was the fact that 66 was the first year for the different bolts/pattern on the heads and they were still possible using the older 64/65 heads to get rid of them?
ddartdude
Well-Known Member
The 920 heads have 1.78 intake valves and the other one has 1.78's as well. The 920's were used on the w/CAP (clean air package) engines. They were also used on the D/Darts which had a version of the W/CAP engines in them.
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moparlee
64 Valiant
Cool, info. Thanks Ddartdude.
ddartdude
Well-Known Member
I like your Valiant MOPARLEE. Had a really nice 64 (driver) that I traded for a 64 Belvedere (project). The Belvedere is still unfinished -- after 10 years. Kind of regret getting rid of the Valiant but the Belvedere has so much more going for it.......like a 426 street wedge and a 4-speed.
Having had 2 D/Darts at the same time, I was able to gather a lot of info on the cars. Still have the race car. Don't think I'll ever part with that. Someday that'll be on the track again. I hope.......................
Having had 2 D/Darts at the same time, I was able to gather a lot of info on the cars. Still have the race car. Don't think I'll ever part with that. Someday that'll be on the track again. I hope.......................
thanks ddartdude,,,,funny that I cant find any info on them,,,just the stock 66 heads,,I've had others say bigger valves,,and others say no way,,,Hey moparlee,,,I just saw your question from last year about the dual quad set-up,,,never installed it yet,,,thats actually a "65" edelbrock dual quad with the different intake angle
2 Darts
A-body Addicted
I've rebuilt a 273 2bbl & a 4bbl. I don't recall any difference in the head. The 4bbl motor had domed pistons to bump compression to somewhere around 10.5:1. Mopar sold a retro fit kit for the 4bbl to upgrade it to D-Dart specs.
FWIW: Here's the text of a dealer notice that went out from Ma Mopar to the faithful.
Dodge Offers "D" Stock Dart
DETROIT -- A new 275-h.p. Dodge Dart GT that meets D Stock specifications of the NHRA, AHRA and NASCAR is now in production. The "D/Dart" has a shipping weight of 2,946 pounds.
The "D/Dart" features a modified 273-cubic inch engine with a special four-barrel Holley carburetor. Other features include:
A special Camcraft camshaft (284 degrees with .495 intake and .505 exhaust), Racer Brown valve springs, a modified, full-breathing intake manifold, a
low-restriction air cleaner, and a Weber clutch. Other standard items are: a heavy-duty 4.86:1 Sure-Grip 8-3/4 inch rear axle, free-flow exhaust headers by Doug of California, a four-speed manual transmission, heavy-duty suspension, and 6.95x14 B.S.W. tires.
The "D/Darts" are regular production line automobiles.
Additionally certain, basic service parts will be available through the Chrysler Parts Division, so that owners of earlier Darts may convert from the 235-h.p. to the new 275-h.p. version of the 273 V-8 engine.
The "D/Dart" has been certified by the sanctioning agencies in the D Stock class. It is expected that this car, properly prepared, will be a top contender.
A high idle speed minimizes roughness, a high numerical axle ratio is used for top acceleration, the distributor is modified for quick advance, and the ignition system is designed for optimum engine output. Due to the expected use of these vehicles, no warranty coverage applies.
Those who are interested in more specific technical details on this car may contact staff engineer Dick Maxwell, Product Planning, Chrysler Corporation, 341 Massachusetts Ave., Detroit 31, Michigan. Phone 313-883-4500, ext. 3947.
In case your local Dodge dealer does not have a full list of the part numbers for these specific components you may wish to contact performance parts specialist Ray Ryder, Chrysler Parts Division, 22631 Lawrence Avenue, Centerline, Michigan. Phone 313-539-3000, ext. 7763
FWIW: Here's the text of a dealer notice that went out from Ma Mopar to the faithful.
Dodge Offers "D" Stock Dart
DETROIT -- A new 275-h.p. Dodge Dart GT that meets D Stock specifications of the NHRA, AHRA and NASCAR is now in production. The "D/Dart" has a shipping weight of 2,946 pounds.
The "D/Dart" features a modified 273-cubic inch engine with a special four-barrel Holley carburetor. Other features include:
A special Camcraft camshaft (284 degrees with .495 intake and .505 exhaust), Racer Brown valve springs, a modified, full-breathing intake manifold, a
low-restriction air cleaner, and a Weber clutch. Other standard items are: a heavy-duty 4.86:1 Sure-Grip 8-3/4 inch rear axle, free-flow exhaust headers by Doug of California, a four-speed manual transmission, heavy-duty suspension, and 6.95x14 B.S.W. tires.
The "D/Darts" are regular production line automobiles.
Additionally certain, basic service parts will be available through the Chrysler Parts Division, so that owners of earlier Darts may convert from the 235-h.p. to the new 275-h.p. version of the 273 V-8 engine.
The "D/Dart" has been certified by the sanctioning agencies in the D Stock class. It is expected that this car, properly prepared, will be a top contender.
A high idle speed minimizes roughness, a high numerical axle ratio is used for top acceleration, the distributor is modified for quick advance, and the ignition system is designed for optimum engine output. Due to the expected use of these vehicles, no warranty coverage applies.
Those who are interested in more specific technical details on this car may contact staff engineer Dick Maxwell, Product Planning, Chrysler Corporation, 341 Massachusetts Ave., Detroit 31, Michigan. Phone 313-883-4500, ext. 3947.
In case your local Dodge dealer does not have a full list of the part numbers for these specific components you may wish to contact performance parts specialist Ray Ryder, Chrysler Parts Division, 22631 Lawrence Avenue, Centerline, Michigan. Phone 313-539-3000, ext. 7763
moparlee
64 Valiant
Wow, that's an actual small port intake with the 64/65 intake bolt size/pattern deal. Killer find.
moparlee
64 Valiant
Thanks Ddart, 426 street wedge and a 4 speed crash box sounds like crap load of fun!
yeah,,,thats why I'm trying to figure out if the heads are the same,,,,thinking of putting the 65 heads on the 66 commando block and runing the dual quad,,I guess I will have to finally pull the 66 heads off and do a side by side comparison,,,,was hoping there were some "experts" on the subject here
cavemanmoron
Well-Known Member
Same size combustion chamber. Use the '65 stuff if you want,
it will work fine, just tuning the dual carbs might be a pain.
Can you tell what engine is in my car, by looking at it?? ;)
dart4 forte i have those same valve covers on my 273 commando
What ever heads are on this commando, they've been modified to fit an aluminum edelbrock LD 340 intake manifold
I took my covers off and replaced them with the old style Direct Connection chrome covers. I'm tired a chasing leakly cast aluminum covers and the chrome covers on now are more period correct.
what dual quad intake are you running?now really up in the air,,,64-65 have smaller heart shaped combustion chamber,66 commando heads more open chamber,,,would the closed chamber bump the comp.ratio up even more than 10:5-1?
I have the 920 heads, cut down stainless 1.88's to 1.84, 1.60 stainless exhaust. bowls blended, radiused, smoothed exhaust, rounded around the guides. They flow 166.9 cfm at .450 of lift with 116% port velocity. Plenty for the 273 combo I'll be running.
pishta
I know I'm right....
JDMopar
Well-Known Member
Dang! This thread is so old.....the cars were almost new when it was started! 
pishta
I know I'm right....
..necro-posting... bringing back the dead BS.
ddartdude
Well-Known Member
Back when I posted this, I had already sold my one D/Dart and was going off the valve sizes posted in Galen's Casting Book -- 6th printing -- Jan 1996. D/Darts had 273 w/C.A.P. engines in them. The intake number is casting number 2536771 and according to Galen's book, the valves on the 920 heads w/C.A.P. are 1.87 x 1.50's which is incorrect. Per all the info that I have from Chrysler, the standard valve gear was used on the cars. Heavier valve springs were used, however, which permits higher engine speeds. It was not advised to operate the engines over 7400 RPM's.
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JDMopar
Well-Known Member
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