1974 318 duster. Can I port/polish these heads and get enough power out of them?

Small Block Mopar Engine

  1. supersoap33

    supersoap33 Well-Known Member

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    Hey all. I bought this duster and it already had some goodies. Holley 4 barrel street avenger carb and edelbrock low-rise intake with a 3" flow master dual exhaust. The exhaust manifolds are the originals, but I can probably change them out and weld them to the 3" flow masters.

    Can I take these heads off, port and polish and keep them? I don't have the money to do much, and keeping things cast is really fine with me. I'm also thinking about putting in new piston rings and an oil pan and rebuilding or just servicing the 904 that came in it so it doesn't leak. And then maybe spending some money and making the rear end a sure grip if they make it with the 8.25. Was also going to put a decent cam in it and change everything to where it works right.

    Thoughts? I don't have a big budget at all.
     
  2. MoparLeo

    MoparLeo NRA BENEFACTOR LEVEL LIFE MEMBER FABO Gold Member

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    Pinch yourself real hard and you might wake up ....
     
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    • Bewy

      Bewy Well-Known Member

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      You will probably have to define your idea of enough power....to be able to answer the question.
       
    • supersoap33

      supersoap33 Well-Known Member

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      300 hp
       
    • RustyRatRod

      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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      You can hit that easily unported. No problem at all.
       
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      • MoparLeo

        MoparLeo NRA BENEFACTOR LEVEL LIFE MEMBER FABO Gold Member

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        Short answer. Unless you have set of templates and experience with a die grinder, proper cutters and a flow bench, more cylinder heads have been ruined than any other engine part.
        Buy/borrow as many engine books as possible before you spend a dime on parts or machine work. Know what you are going to do ( Have a plan) before you do it.
        To bake a cake you have to know what ingredients you are going to use, what order to mix the ingredients and what proportions of each ingredient you are going to use. How much time mixing and baking.
        And then it might come out the way you thought it would.
        Just putting different ingredients together without a recipe will get you nothing but something to throw away.
         
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        • Dave Huth

          Dave Huth Well-Known Member

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          3” exhaust is overkill for the 318, you won’t get the proper scavenging effect and actually might be losing power. Carb, intake, cam , exhaust, etc. must match to make a good formula. Bigger isn’t always better if disproportionate.
           
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          • RustyRatRod

            RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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            I don't know. I never have supported the "needs a little back pressure" theory. I think if he can afford the 3" system now, it'll be there when he upgrades later on. It's certainly not gonna make the difference between it having good power and not.
             
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            • 448Scamp

              448Scamp Running Free

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              There is never a scenario where back pressure is a good thing. Tubing diameter and length affect more than scavenging. Cam timing will affect which exhaust sizing will affect combustion chamber scavenging much more than sizing. Get that wrong and the engine will be unaffected by whatever exhaust is bolted to it.
               
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              • RustyRatRod

                RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                I'm kinda in agreement. Every single time without fail when I've gone up in header tube size and or exhaust pipe size, I've always gained more power. With no exception.
                 
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                • toolmanmike

                  toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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                  Way back when, I put a set of Mickey THompson Try Y's on my 340 in my 73 Challenger and off to the strip I went. With no further tuning or modifications it went slower by a few hundredths. The stock manifolds and exhaust must have been pretty good back them. Good thing I kept all the old parts to put back on. A awful lot of work for no gain.
                   
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                  • cudamark

                    cudamark FABO Gold Member FABO Gold Member

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                    I haven't heard what sort of budget you have here, and what is most important to you. You start adding horsepower, and the rest of the drivetrain might need upgrading too depending on how you plan to drive it.
                     
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                    • 67Dart273

                      67Dart273 FABO Gold Member FABO Gold Member

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                      Is it a stock 318 cam? "A bit more" cam might help depending on what is in there. Do NOT go overboard on a cam. Guys on here can advise. "Back in the day" I would have put a 340 cam in

                      Also just exactly "what is" the intake? What model?
                       
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                      • 273

                        273 Well-Known Member

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                        318 Long Block Bolt Ons - Tech Articles - Mopar Muscle Magazine

                        318 Engine Buildup & Dyno Test - Mopar Muscle Magazine

                        Magazine Builds post #27
                         
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                        • 273

                          273 Well-Known Member

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                          I'd look for some 360 heads do a little porting and milling.

                          whatever you do to 318 heads if you do to 360 heads you'll have at least 30-40 hp more.
                           
                          Last edited: Jul 30, 2021
                        • j par

                          j par Well-hung Member

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                          I've been off by a half second just cuz the air was bad...
                           
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                          • TT5.9mag

                            TT5.9mag Two atmospheres are better than one

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                            The reason should be obvious.
                            To the op leave the stock cam in it for now. Focus on tuning and get it dialed in really well. Timing and carb. Most people don’t spend enough time sorting this stuff out. Build your diff with a sure grip and your choice of street gears 3:23-3:55. Then put a good converter in it, Around 2800 stall. It will surprise you how well your car will run in that state. Especially if you get the tune dialed in.
                             
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                            • TT5.9mag

                              TT5.9mag Two atmospheres are better than one

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                              For a cheap and easy upgrade on cylinder heads, get a set of magnum heads and appropriate valve gear from the junk yard. Have them checked out by a machine shop and run em. They’ll be better than the stock heads and much easier than porting yours.
                               
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                              • 67Dart273

                                67Dart273 FABO Gold Member FABO Gold Member

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                                You don't want 360 heads on a 318 unless you can do something with the compression. They will drop already low compression to the basement, unless you use something like the 302 heads
                                 
                              • cudamark

                                cudamark FABO Gold Member FABO Gold Member

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                                302 castings are 318 heads. I think you may be referring to the 360 equivalent, which is a 308 casting.
                                 
                              • 67Dart273

                                67Dart273 FABO Gold Member FABO Gold Member

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                                I may have recollected wrong no. I was thinking of the small cc heads
                                 
                              • 273

                                273 Well-Known Member

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                                Why i said mill, you need to take something like .030-.040" off to have same chamber size as 318 heads, 302 heads are just like any other 318 don't flow enough and the CR advantage get ya like 2% power increase that's like 5hp, 10hp at best, if you want closed chamber magnum would be a better choice and can handle 400hp without porting. LA 360 can handle around 375 hp without porting.
                                318 heads 300 maybe 325 hp without porting. were talking low cr and reasonable cam sizes here for power output.
                                 
                              • MOPAROFFICIAL

                                MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                                I can make a 318 head touch 190's with just a really good .070 wide face 4 angle valve job.
                                The stock cam is X amount- .395/.400ish of lift..with rocker arms that are advertised @1.5 , but are really less..
                                Low lift flow would be the focus if staying with the stock cam n only working the heads. Porting will increase flow at all lifts if you know what you're doing... but a good 4 angle valve job is idiot proof.imo

                                Otherwise...just open the bowl, profile guides, mildly work the straight atop the ssr approach to the turn itself...with the common wall. Leave lip/tiny edge just before it turns on that side of the approach.

                                Open chamber near seat like a cone, angled to the edge of the chamber. Don't hog it flat to the chamber wall.

                                If you lay a head gasket on the deck line it up with some spark plugs or what-have-you corks, use a wide tip marker for 318 and that distance of the line you leave should be the bores actual edge and let you know how far to go. With 360s and 340s you just use a regular Sharpie fine point and that's near perfect to show bores actuall boundry line/edge.

                                Lightly flatten 'not completely' the roof kink in exh ports, lightly roll the ssr over to the floor 'u shape and not flat angled back. Make a venturi if you can in far side bowl/throat.
                                Snap gauge width at ssr of exh and exit and open them accordingly. Pay attention to the ports design shape and how we're trying to work with that on the exhaust.. 'ends vs the center exh ports' for instance.
                                 
                                Last edited: Jul 31, 2021
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                                • diymirage

                                  diymirage HP@idle > hondaHP@redline

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                                  More if you also switch out the block for a 360

                                  :poke:

                                  tenor-3.gif
                                   
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                                  • 273

                                    273 Well-Known Member

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                                    Lol true at least more torque anyways :)

                                    A 5.9 magnum makes 300 hp as is and I’d bet the 5.2 magnum ain’t to far behind
                                     
                                    Last edited: Jul 30, 2021
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