273/4 -318 debate

Discussion in 'Small Block Mopar Engine' started by pishta, Nov 10, 2018 at 10:38 AM.

  1. pishta

    pishta I know I'm right....

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    Were having a discussion on the merits of the 273-4 engine compared to the 318-2 of the following years, sometimes even the same year. Sure the 273-4 was a hot motor back in 65 when it was the best thing between the fenders of the early A's but you just can't deny that a 20% larger motor is going to make a difference. Performance test are all over the board, depending if the dufus can drive or if the dyno is set up properly, yadda yadda...but I found a site that has a lot of info on cars in general and has generated graphs (from factory data) on performance specs. So I tried to match 2 like cars (in weight, gear and transmissions) with our 273-4 and the 'new' 318-2. Results? Well, I think it would ultimately come down to the reaction time between these 2 motors as they are pretty close. You can see the shift points are higher on the smaller higher winding 273 and the torque advantage goes to the 318 down low. Theoretical top speed goes to the high winding 273 due to the cam profile and possible higher RPM potential of its heavier valve springs and forged crank.

    1965 273-4 Barracuda
    reference weights: shipping weight 3029 lbs base curb weight: test weight 1430 kg / 3152 lbs
    how fast is this car ? top speed: 126 mph (©theoretical);
    accelerations: 0- 60 mph 6.9© s; 0- 100 km/h 7.3© s (simulation ©automobile-catalog.com); 1/4 mile drag time (402 m) 15.6
    273g.jpg







    1968 318-2 Barracuda
    reference weights: shipping weight 1363 kg / 3005 lbs base curb weight: 1430 kg / 3152 lbs
    how fast is this car ? top speed: 178 km/h (111 mph) (©theoretical);
    accelerations: 0- 60 mph 6.8© s; 0- 100 km/h 7.3© s (simulation ©automobile-catalog.com); 1/4 mile drag time (402 m) 15.4© s

    318g.jpg



    overlaid


    compare.jpg

    <<<lower 75 from tq curve points to align 5250rpm intersection>>>
    <<<the tq graph should start at 100 so the data points align SAE>>>

    and the overlay of the HP/torque curves from factory data. increased displacement really shows in the torque curve but the smaller 273 can hold its HP peak longer. This is due to camshaft differences. Put a similar cam in a 318 and its curve would change.



    Bottom line: in a 1/4 mile race all things being somewhat stock on these 2 cars, the 318 would edge it by .2 seconds..theoretically. Now on the highway having some fun with your buddy, the 273 would probably walk away after 4500 RPM. Now put the 4bbl cam in the 318 and it would probably be a 20% increase across the board on the 318 data. To say the 273-4 would walk a 318-2 in a drag race is not supported in this data. All data is from blueprint specs and we all know how well those are kept in production, especially compression ratios.
    Food for thought...or to fling?
     
    Last edited: Nov 11, 2018 at 10:48 AM
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    • 318willrun

      318willrun Stomper 4x4... we kept energizer in business

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      Are we talking a 273 commando vs a 318 2bbl ? Not really apples to apples. Equally built, 318 wins no brainer. Same stroke, much bigger bore, same heads. Give them both the same cams, same carbs, same compression, in other words all equal, hands down 318 wins.
       
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      • pishta

        pishta I know I'm right....

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        yes we are for debate sake, and i agree with you 100%
        And I just realized there are no graph lines.....that doesnt help does it?
         
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        • clifftt

          clifftt Well-Known Member

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          Yea, I was wondering what I was supposed to see. :rolleyes:
           
        • pishta

          pishta I know I'm right....

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          there we go, wonky paint end around as the line data is superimposed on a template I guess.
           
        • toolmanmike

          toolmanmike FABO Staff Staff Member FABO Gold Member

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          This will be a fun thread. Thanks for starting it.
           
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          • pishta

            pishta I know I'm right....

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            its been under way for a few posts over on "numbers matching" thought I would unjack that thread and start a new....
             
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            • Mattax

              Mattax Just the facts, ma'am FABO Gold Member

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              Anyone have some magazine tests from back in the day?
              I have the Brooklands reprint for the Barracuda, which has several with the 273-4bbl but none for the 318 2 barrel.
              Thought it would be interesting to see how close the sim is to the magazine tests.

              Motor Trend Jan 1965, 4 speed. 3.55 rear
              0-60mph: 8 seconds with two people in car.
              1/4 mile: 16.1 seconds, 87 mph

              Hot Rod March 1965. Torqueflite, 3.23 rear, curb wt 3250 lbs.
              0-60mph: 10.3 seconds
              1/4 mile: 17.7 seconds, 79.3 mph

              Car and Driver June 1966. Torqueflite, 3.23 rear, curb wt 2820 lbs., test weight 3100
              0-60mph: 9.1 seconds
              1/4 mile: 17.6 seconds, 81 mph
              [I have no idea how they got the wieght so low! Typo? editing error?]

              Car Life Road Test March 1967. Torqueflite, 3.23 rear, curb wt 3310 lbs., test weight 3720, D70-14 Firestone Wide Oval
              0-60mph: 9.2 seconds
              1/4 mile: 16.9 seconds, 85.6 mph

              Not as consistant as I would have liked to see.
              My guessese are
              '65 had the advantage of lowest weight and better gearing for the 1/4 mile.
              '67 had torqueflite had just the front pump and perhaps a better timing curve and/or some other tweaks that helped top end.
               
            • perfacar

              perfacar Well-Known Member

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              in stock eliminator, 318 2 bbl, runs 12.90,s the 273 runs 11.70,s both cars are prepared stockers, the 2 bbl cannot run with the 273 4 bbl.
               
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              • pishta

                pishta I know I'm right....

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                How are those prepped? Are we talking A D-Dart spec 275/273 with 4.56 gears? 11.9 sounds very quick. The whole debate was originally what a 318 can do against a 273, all things being equal 'cept bore. Lets do a 4bbl 10.5:1 318 with a 425/248 duration cam and put it up against a 273-4 with same cam. My initial direction was there is no use building a 273 if you can build a 318 with the same specs minus the bore. Same goes for building a 318 if you can build a 340 (not counting the larger head of the 340).
                 
                Last edited: Nov 10, 2018 at 4:05 PM
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                • toolmanmike

                  toolmanmike FABO Staff Staff Member FABO Gold Member

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                  Yep, not talking about purposely built race cars.
                   
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                  • AJ/FormS

                    AJ/FormS 367 FormS clone 3.09-1.92-1.40-1.09-.78od 3.55s

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                    As a streeter
                    Here is my favorite comparison. Both geared with 3.23s and 904s what happens when you floor it at 25 mph or so, and the trans downshifts. This comes to about 2700 rpm. I know which one I would want.
                    If you stop the race at 40/45 as is often done in a 35zone, they have both reached peak power..... but the 318 has put down significantly more average power during the trip. I know which one I would want.
                    And my favorite; check out the difference at say 2250 Rpm, the typical; stall one might choose. That is around 125 ftlbs/50hp difference right there. The little 273 is gonna need a lotta TM to make up for that. Of course if the 318 lights up the tires well, that's that then,lol. But there are solutions for tirespin. Not much for the 273 torque at 2250,lol.
                    HANG ON this does not compute!!
                    Wait, I think there is something wrong with the calibrations....the lines should cross at 5250.
                    And how many 318-2s make 460 ftlbs
                    And if they did that at 2750 the HP would be 240....... not 180ish
                    I'm confused,lol






                    compare-jpg.jpg
                     
                    Last edited: Nov 10, 2018 at 4:53 PM
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                    • circlepilot

                      circlepilot FABO Gold Member FABO Gold Member

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                      Back in the day...1966...My 65 Barracuda 273/4 Commando, 4 speed, 14" wheels 7 1/4 rear, was with out doubt one of the fastest "city block" runners in the City of North Miami. It never ran in the (1/4 mile) upper elevens but upper 15s and lower 16s were a given. I ran F/PS and F/S at the Miami Hollywood Speedway. Falcon Sprints, 390 Fairlanes, 289 Fairlanes and 318/2s, were easy pickings in city block runs, especially 1st gear rolling starts. Bunch of dudes were glad to see me join the Air Force. Then I went on to terrorized the local hot rods in Dover Delaware, even the new Camaros. Yeah! My 273 was a real hot rod, with a few added goodies, however its weak spot...the little clutch and the 7 1/4 rear end, no L/S, (that I wiped out several times) which eventually got replace with a modified 8 3/4 out of a Dodge Polara station wagon, still had the small clutch though. I got stupid in 1974 and traded for a new pick up truck.
                       
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                      • '63GT

                        '63GT Well-Known Member

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                        I agree wholeheartedly..
                        I never could understand hunting, high and low, for a 273 when 318's are EVERYWHERE. (sometimes free)
                        In fact, as hard as it is to scare up a 340, why not build a 318 with 340 parts (heads etc)? You're only a few ci short of a 340, without the co$t. (just use a domed 318 piston for CR)
                         
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                        • Garrett Ellison

                          Garrett Ellison Amateur driver on public roadway, do not imitate!

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                          Indeed, a fun thread... The rating on the four barrel of the 273 was 460 CFM but the stock carter bbd on a 318 is only rated at 285 cfm. This alone will give the 273 a considerable edge over the 318 two barrel. Another factor would be distributor curves and timing, I'm pretty sure the timing curve and the static timing on the 273 commando engine would be much more oriented toward acceleration than the economy oriented 318 2 barrel. Then there is the whole deal with 318 compression, or more adequately, lack thereof... It would be interesting to take a stock low compression 318 two barrel, re-curve distributor and optimize the timing, circular file the stock air filter assembly for a low rest air cleaner, and add dual exhaust. To truly make all else equal, start with a stock 273 commando car with decent gearing, get a baseline and optimize everything, then swap in the 318 and see what happens... everything considered that stock 318 cam is still going to be a major disadvantage!
                           
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                          • perfacar

                            perfacar Well-Known Member

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                            1966 valiant 235/273, ran 11.65 at Pomona yesterday. the 318's are from the Midwest, both are 1968 cars.
                             
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                            • 318willrun

                              318willrun Stomper 4x4... we kept energizer in business

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                              I've gone 15.9's with a 100% bone stock 318 2bbl (added dual exhaust to factory manifolds) in a b-body with 2.94's. Manual steering, manual brakes.
                               
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                              • '63GT

                                '63GT Well-Known Member

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                                I heard about those guys... what are they running for headers? Do you know?
                                 
                              • 318willrun

                                318willrun Stomper 4x4... we kept energizer in business

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                                But stock eliminator is so far from stock, it almost makes the comparison pointless.
                                 
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                                • Garrett Ellison

                                  Garrett Ellison Amateur driver on public roadway, do not imitate!

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                                  But i do agree, I can get a 318 core within 24 hours or less to start a build, order some flat top KB's or even cheapo sealed power pistons (presently guilty!), zero deck the block after getting the rotating assembly fully indexed and equalized, followed by getting the intake flange of the heads milled to compensate for the lower deck and build a 10:1 to (up to a 12:1 with KB domes!) 318 for not much more cost than a standard rebuild. Of course, I already have a 75 model 360 core for the future, if ever I get the rest of the car ready to handle a stroker build and get bored swapping parts on the 318...
                                   
                                • pishta

                                  pishta I know I'm right....

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                                  Thats ok, its in Metric.....Its a Euro data site. Maybe if we figure out what a Nm is to ft/lb maybe it will skew the knows intersection point to the 5250 ASE standard?

                                  View attachment 1715247248
                                   
                                  Last edited: Nov 10, 2018 at 5:52 PM
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                                  • pishta

                                    pishta I know I'm right....

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                                    thats a 425HP motor plugged into an ET calculator @ 2900 lbs! Thats a stout 273.
                                     
                                  • Garrett Ellison

                                    Garrett Ellison Amateur driver on public roadway, do not imitate!

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                                    While we are on topic here, I am curious who has the highest output 318 on here, by the time I am done playing I am planning on 12:1 plus compression with mildly ported 318 heads and a solid lifter Lunati drag race cam just to see what the upper end of 318 performance is. There is a ‘68 ‘Cuda drag car with a W2 318 on YouTube that is certainly stout. I know it probably won’t last very long but it should be a whole lot of fun while it does last, Lolol!
                                     
                                    Last edited: Nov 11, 2018 at 10:47 AM
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                                    • pishta

                                      pishta I know I'm right....

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                                      post 'em up! What do those 5.2's run?
                                       
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                                      • 318willrun

                                        318willrun Stomper 4x4... we kept energizer in business

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                                        in stock 2bbl form???? they did make 318 4bbl's too....
                                         
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