Hands On We should probably clarify this article's headline right away. By hemi power, we mean factory-rated horsepower for something like a '68 Hemi Roadrunner, and by half the cost, well, that's self-explanatory. The relatively low cost is why this build is running in this issue. Brian Hafliger of IMM Engine and Dyno was able to take a lowly 400 block and piece it together with a clever combination of used factory parts, some good machining, and a mild aftermarket cam kit, and make as much factory-rated horsepower as the mighty Dodge and Plymouth 426 Hemi engines in '66 through '71 Dodge and Plymouth cars. Best of all, aside from the machining, this engine can be built at home. There were no exotic parts in this engine, and no black-magic porting was done to the cylinder heads or intake manifold. Mopar fans, start scrounging eBay or your local swap meets and salvage yards. Grab yourselves a 400, and make some power. On the Dyno We were honestly surprised by the power this combination made. None of the random guesses from the peanut gallery crowding around IMM's dyno cell were this high. Brian and his dad were hoping for about 415 hp, but everyone else guessed lower than that. All eyes widened as the horsepower figures crested 415 on the very first pull. After just minor tweaking to the carburetor jetting and advancing the timing by 2 degrees, we achieved a peak horsepower number of 426.7 at 5,700 rpm, the same as what the 426 Hemi in Roadrunners and Chargers were rated at. There may actually be a few more ponies lurking inside this engine, but Brian didn't feel comfortable pushing the engine too much farther. The weak links in this combination are the OE-style rocker arms, which weren't designed for the spring pressures and engine speed we were asking of them. If you are looking to replicate this build but have a little more money to spend, consider a rocker-arm upgrade. Otherwise, this is an engine you could drop into a classic Mopar and surprise a few people with the power you're getting from what was never really considered to be a performance engine. *Note: These are IMM's prices. Your local machine shop's costs will vary. Manufactured throughout the '70s, Chrylser's 400 is a larger-bore variant of the 383. Technically, both the 383 and 400 are B engines, having a lower deck height than the RB blocks (9.980-inch versus 10.725). The 400 is hugely oversquare with a large 4.342-inch bore and a tiny 3.38-inch stroke, shorter than a 350-inch small-block Chevy. That big bore size helps the engine breathe, because the cylinder walls do not shroud the intake and exhaust valves, making this block an interesting choice for a potentially high-rpm powerplant or an ideal candidate for a stroker crankshaft.Manufactured throughout the '70s, Chrylser's 400 is a larger-bore variant of the 383. Tech We stuck to the basics for this build. Brian found a used 383 crankshaft and bolted it in. While the 383 and 400 crankshafts have the same stroke, many 383s had forged cranks, while 400s rarely did.We stuck to the basics for this build. Brian found a used 383 crankshaft and bolted it in. The connecting rods are stock 400 parts. Hafliger resized the rods after installing ARP rod bolts. He reused the stock main bolts so he wouldn't have to align-bore the main caps, but he did bore the block 0.030-inch over and installed off-the-shelf pistons.The connecting rods are stock 400 parts. Hafliger resized the rods after installing ARP ro Highly recommended is 440 Source's billet aluminum rear main cap. "They hold the rear main seal better. We've never had an oil leak when we used one of these," says Hafliger.Highly recommended is 440 Source's billet aluminum rear main cap. "They hold the rear main Typical of the era, these were low-compression engines, and the decks weren't square when he first mocked up the engine. Hafliger milled the block 0.027 inch on one side and 0.019 from the other to square the block and set the pistons to zero deck. The pistons and their corresponding 5/64-inch rings weigh a hefty 856 grams.Typical of the era, these were low-compression engines, and the decks weren't square when Prior to the valve job, Brian cleaned the bowl area of the combustion chambers. This is work that any competent machine shop could do, and it would not be considered porting. Other than smoothing the transition from the ports to the seats, no other work was done to the cylinder heads.Prior to the valve job, Brian cleaned the bowl area of the combustion chambers. This is wo Hafliger also milled the cylinder heads 0.050 inch to reach his goal of a 9.8:1 compression ratio. Unlike open-chamber big-block Chevy heads, these 906 castings (popular on 440 engines) have shallower, 86cc combustion chambers. Milling the heads brought the volume down to 79 cc. He replaced the original valves with Manley parts of the stock diameter (2.07-inch intake, 1.74-inch exhaust). He performed a standard, three-angle valve job and a 20-degree back cut on the intake valves before installing them.Hafliger also milled the cylinder heads 0.050 inch to reach his goal of a 9.8:1 compressio We chose Comp's Thumpr cam kit, which includes the cam, the timing set, lifters, valve springs, retainers, locks, and seals—a lot of stuff for $500. The cam specs are 227/241 degrees duration at 0.050 with 0.486/0.473 valve lift with 1.5:1 rocker arms and a 107-degree lobe-separation angle. Hafliger installed the cam straight up.We chose Comp's Thumpr cam kit, which includes the cam, the timing set, lifters, valve spr To save some money, we decided to reuse the factory shaft-mount rocker arms. These aren't strong parts and are notorious for shooting pushrods out through the rocker at high rpm or with heavy valvesprings. However, they survived this engine's 5,700-rpm dyno pulls.To save some money, we decided to reuse the factory shaft-mount rocker arms. These aren't 1 | 2 | » | View Full Article By John McGann Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!
