318 Torque Build

Small Block Mopar Engine

  1. superdart

    superdart Shade Tree Tinker Gnome.....

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    Just getting some input. I've got a '77 M880 (W200 Power Wagon) with a 318, 727/NP203 (full time 4wd) and 4.10s on 33" tires. The engine is original, under 100k miles, but a bit of idle time after belonging to a narcotics task force.

    For now I'm doing some maintenance and running the engine with some upgrades:

    625 Carter AFB
    Wiend Stealth dual plane
    MSD Streetfire, Pertronix distributor, wires
    1-5/8" block huggers

    What I'm thinking of is what I want to do long term. Being a truck I'm looking for torque, and an RPM range to go with the tires and gearing. In the future it may get a 518 to knock the highway RPMs down...but even that will still turn 2k+ at 65mph.

    Yeah, I know...do a 360....but I also might have access to a NIB Mopar 3.58" stroker crank (ironically one I sold, but my friend never used). I'm thinking do that with the right cam and moderate compression, revalve and port the heads.

    Thoughts? Cam and compression ideas?
     
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    • Bewy

      Bewy Well-Known Member

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      Great carb.
      Cam? It would be different if you stroke the engine, so you should decide yay or nay on the crank, & then a more accurate cam selection can be made.
       
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      • superdart

        superdart Shade Tree Tinker Gnome.....

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        I ran the carb on my Dart for many years before I converted it to EFI. It's been sitting on the shelf for 5 years, so this seems like a good way to use it. The Wieand and distributor were awesome deals from the discount shelf at Summit.

        For argument sake, lets say I stick with either the 318 or go with the 346 stroker. I would do a minimum bore to clean it up in either case. I have the heads off now and the cylinder walls look great. Interestingly, at TDC the piston is only about .08 in the hole. I expected it to be a bit deeper.

        I'm not trying to make it a power house...but I'd like it to have some grunt if I needed to put a car trailer behind it (Texas, so pretty flat around here).
         
      • RustyRatRod

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

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        Piss on the 360 the 318 is a fantastic low rpm torque truck engine. Along with the other mods you've already done, a good mild cam choice will really shine.
         
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        • RustyRatRod

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

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          • 496 polara

            496 polara moparts id gch

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            HAVE THE HEADS PORTED.AIRFLOW MAKES EVERYTHING ELSE SHINE.
             
          • Garrett Ellison

            Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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            Another member here has an 886 (ambulance version) with an Offenhauser dual port, Edelbrock 1406, an Isky 3901M Mile-A-More, and a mild distributor recurve.
            Isky Racing Cams 3901M Mile-A-Mor Cam | Creative Motoring, LLC

            He says the torque is worlds away from stock. I do recommend a pair of magnum exhaust manifolds (they’ll clear the column shift setup nicely) and a pair of 2-1/2 inch pipes to a Jones Racing dual in & out motorhome muffler
            on the right side.
            Jones Exhaust SD726-3F Jones Exhaust Full Boar Round Super Duty Mufflers | Summit Racing
            I like the Lunati high efficiency grind better, but if you can’t find one, summit shows comp has this similar grind in stock.
            DODGE COMP Cams 20-220-3 COMP Cams Xtreme Energy Camshafts | Summit Racing
             
            Last edited: Nov 25, 2021 at 8:16 AM
          • krazykuda

            krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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            Get some 10.5 compression 318 pistons and then put a set of 340/360 heads on it... Mild port the heads and install hardened seats in the exhaust side...

            The larger combustion chambers of the 340/360 heads will get you back down to the 9.2 compression range - perfect for a street driver on pump gas... And the ports of the 340/360 heads flow better...
             
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            • AJ/FormS

              AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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              4.10s and 33s are the equivalent of 3.23s with 26" tires. So I imagine, if it still has the stock lo-stall TC in it, that she's a bit of a slug on take-off.
              Normally aspirated there are only three ways to get off the start-line quicker;
              1) is a higher stall, and
              2) is more cylinder pressure.
              3) is more cubic inches.

              > if the 318 has to stay, then more stall is usually the best choice. Going from say 2000 to 3000, your 318 could be 100 ftlbs stronger, which could translate to more than 100 horsepower.
              > if you stroke it to 349; this is a change of ~10%.. With no other changes and a stock stall (guessing 2000 or less), 10% is not a very significant change. I mean at WOT and 2000 rpm, you might be looking at 10horsepower difference.
              > if the 4.10s have to stay, more cubes at same stall will help. But cubes, compression AND stall would of course, be the cat's meow. This gear/tire combo will force your engine, into a low-rpm situation until about 3300rpm/30mph; so no matter what you do to the engine in terms of bolt-ons, nothing will make a significant improvement. Only the Higher-stall will get you moving quicker.
              >A bigger cam usually has a later-closing intake valve, and so, with no other changes, will lose cylinder pressure, making the zero MPH take-off yet softer.
              > if you install a 4bbl the power does not begin increasing until the capacity of the current carb is exceeded, which could be around 3000 rpm. With no tirespin and your current 4.10s/33s, this could be 27mph. If you make the secondaries open at zero mph, chances are very good with a 2000TC that she will just bog.
              IMO
              Of all these options; the higher-stall TC should be the very first Go-To. After that should be gears; but to be significant, it would need to be at the very least 10%, so 4.56s. But this only brings your speed down at 3300 from 30 to 27mph, so not the best idea. You can get the same 10% with the 3.58 crank. And then you also get the opportunity to increase the cylinder pressure. That's a 3-fer; More displacement/more low-rpm torque, plus more pressure, plus a slightly higher stall on the stock TC.
              But since the engine is out, now's the perfect time to up the stall. And since the engine is completely torn down, now is the perfect time to up-cam, and optimize the pressure to it.

              Now;
              since you already have the 4bbl, do yourself a favor; With whatever is currently on it, do some time-trials to 27 or so mph, and average them out.
              Then after you get the 4bbl on and working, do the time-trials again to 27mph; no cheating, cuz you'd only be cheating yourself. Now calculate the difference and convert it to a percent decrease in time, if any......... You don't have to publish it, this is just for your own satisfaction.

              In any case; Happy HotRodding.
               
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              • Garrett Ellison

                Garrett Ellison Amateur driver on public roadway, do not imitate.. FABO Gold Member

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                With the pistons.080 down hole, I would probably look at a set of sealed power four relief cast pistons and getting the block decked to zero, too. But if I went that far into it I would do the extra stroke (if you can find the pistons) and that crank has the smaller 318 main size. If they weren’t so expensive, an NV4500 out of a magnum powered later truck with the married 205 ( 3/4 ton HD or full ton) or 238 (1/2 ton or regular duty 3/4 ton) transfer case and installing locking hubs would be fantastic. If you can find one, a 1981-1985 non CAD 3/4 ton axle with manual hubs is a good upgrade, too. If not, be sure to keep your hub bearings greased, especially with a lot of highway usage. I’ve been in enough NV swaps and can tell you that you’ll have to convert to the factory hydraulic slave cylinder clutch setup but no automatic comes close for the performance in a heavy truck, especially when towing.
                 
              • rumblefish360

                rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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                Thoughts….

                Decide up front on engine size. Like Bewy said, the engine size will dictate the cam to use.
                Your block hugging headers need to go. The longer the tube for the header (within reason) will provide more torque over a shorter tube. Then run a collector extension between 16 & 18 inches into a pressure wave cancellation box. This helps produce maximum torque. Exhaust tube should be 2-1/2 inches. Use a X or H pipe after the cancellation boxes.

                Cam, should not be a split pattern. A single pattern cam makes more low end torque. Just a few foot pounds, but everything adds up to something so keep piling the little things up.

                Compression and heads.

                If you rebuild it, add some hood compression to it. Iron heads at 9.5-1 and a max of 10-1 if you can get 93 octane. Aluminum can be a good help as well and can add a little more compression. (About 1 point more.)

                Have your heads well prepped with a good racing valve job. A bigger set of valves (2.02-1.60) are good to use for this. A bowl porting is a big plus.

                Research your cam carefully!
                 
                Last edited: Nov 25, 2021 at 7:06 PM
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