318 differences 1972/1973

[jakuzzie]

Hi guys!

I just bought my first mopar. It's a 1973 Duster and it has 318 engine.
What are the main differences between the 1972 318 (230hp) and the 1973 318 (150hp)?
Which parts do i need to get the 230hp out of the 1973 318?

Thanks!

 

[Abodybomber]

Hi guys!

I just bought my first mopar. It's a 1973 Duster and it has 318 engine.
What are the main differences between the 1972 318 (230hp) and the 1973 318 (150hp)?
Which parts do i need to get the 230hp out of the 1973 318?

Thanks!

The U.S. government "changed " horse power ratings from SAE "gross" flywheel rating ,(1972-1973 -wish..) to "net " rear wheel horsepower ratings ( think chassis dyno)..
A better idea: Is it completely stock?, or have "goodies " been added ( headers,aluminum intake can, four barrel carb) ? This is needed to know... I wouldn't personally worry about factory h.p. ratings,unless going completely O.E.M. stock.(just my opinion).

 

[Dartnut]

They are pretty much the same engine except for the way they were rated as mentioned above.

 

[krazykuda]

Bomber is right.

The 72 & 73 318 both have the same compression and camshaft. the only difference in the output is due to the new way of rating....

 

[jakuzzie]

Thank you for the answers! :cheers:

 

[nm9stheham]

As best I can recall from those days, actually the HP rating change was still at the flywheel, not the rear wheels, but the mfrs had to start putting all the accessories on the engines and such. Prior to that, they would sometimes even measure HP without water pumps to get max HP!

Plus, 1973 was the first serious year of emissions and for new cars to use the new-fangled no-lead gas in the USA. There were leaner carbs to reduce CO and HC emissions, which required retarded timing to avoid knocking. And it lowered compression for some engines for lower NoX as well as retarded timing (but I suspect not the low CR 318).

So just getting the ignition timing right and getting a well tuned carb on the car will get you a long ways. Plus all the usual upgrades to cams and manifolds.

OP, are you rebuilding the engine, or just making changes from the outside?

 

[67Dart273]

Another little "side note" about the early 70's. Many guys proclaim "I don't have EGR" because they don't have a visible EGR valve.

Well, sorry, but..........the first couple of years Ma put EGR on engines, "all she did" was to drill a couple of holes (functionally) into the floor of the manifold and "bleed" exhaust up from the crossover.

Only way to tell is to look down into the intake

A crop from the shop manual:

 

[273]

A 4 bbl, duals and a cam like comps 265 will get you in the 230 hp net range though.

 

[2 Darts]

Hi guys!

I just bought my first mopar. It's a 1973 Duster and it has 318 engine.
What are the main differences between the 1972 318 (230hp) and the 1973 318 (150hp)?
Which parts do i need to get the 230hp out of the 1973 318?

Thanks!

Main differences are:

Drop in advertised compression ratio from 9.2:1 to 8.62:1.
Hardened valve seats on 73 & later 318.
Change in horsepower rating from gross rating to SAE net. nm9stheham has it right.

As best I can recall from those days, actually the HP rating change was still at the flywheel, not the rear wheels, but the mfrs had to start putting all the accessories on the engines and such. Prior to that, they would sometimes even measure HP without water pumps to get max HP!

The compression ratio change was accomplished by a combination of larger cylinder head combustion chamber volume and lowering piston deck height. The "tallest" pistons were used from 67-69. Piston deck height was reduced a little bit in 1970-72 engines, but the advertised compression ratio did not change, IIRC.

 

[67Dart273]

A 4 bbl, duals and a cam like comps 265 will get you in the 230 hp net range though.

At the time I tore mine down for paint, I had a 73 or so 318, mild cam "about same" as a 340, Ed Performer Intake and 4BBL injection, same as a 4BBL With 3.7X gears the thing was snotty as all get out.

 

['73red-duster]

HP thing changed in '72. My '72 Duster 318 was 150 hp, iirc '71 was 210. Not a nickels worth of difference in them other than how they were rated.

 

[krazykuda]

Compression:

67 - 69 318 had 9.2 compression.

70 - 71 had 8.8 compression.

72 - 75 had 8.6 compression.


Camshafts:

67 US had 244/244/22 .390/.390 lift 14-50-56-8
67 Can had 248/248/26 .390/.390 lift 14-54-56-12

68 - 70 had 240/248/20 .373/.399 lift 10-50-58-10

71 - 75 had 240/248/26 .373/.399 lift 10-50-52-16


All per factory service manual.

I don't go beyond 75.....

 

[AJ/FormS]

Another little "side note" about the early 70's. Many guys proclaim "I don't have EGR" because they don't have a visible EGR valve.

Well, sorry, but..........the first couple of years Ma put EGR on engines, "all she did" was to drill a couple of holes (functionally) into the floor of the manifold and "bleed" exhaust up from the crossover.

Only way to tell is to look down into the intake

A crop from the shop manual:

Check it out; FULL-TIME EGR.
Hot,cold,summer n winter, Idle, PT,WOT. What were they thinking?
I have a couple of those wonders; any takers?
The one redeeming factor was you could unscrew the jets,braze them shut, put them back in,and nobody was the wiser.
It's almost surprising how well those old girls actually ran, with those working.