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Build Your Own 455HP Pump-Gas Magnum V8 For Around $4,000!

HOT ROD logo HOT ROD 8/10/2017 Hot Rod Network Staff
001-budget-sledgehammer-5.9l-magnum-smallblock Build Your Own 455HP Pump-Gas Magnum V8 For Around $4,000!

Pretty much every day, a magazine or media outlet gets slammed for touting "cheap horsepower." There seems to be a disparity between what readers and the media define as affordable, so before we continue let's try to clear that up. Here at Mopar Muscle, something that is built on a budget is not going to be a grenade with the pin pulled, nor is it going to rely on some unobtainable tidbit we're relying on you to pull out of a mythical scrapyard. In our quest to build the Budget Sledgehammer—our 5.9L Magnum small-block—we faced the fact that most are going to head to the internet to order their parts new. The one exception to that is the basis for our build-up—the donor core 5.9L Magnum engine itself.


Of all the Chrysler V8s, no other engine is present in salvage yards in greater numbers, except perhaps the 5.7L Hemi. And while the Hemi might arguably be more numerous, the Magnum is certainly less expensive. In useable form, these can typically be picked up for well under $500—sometimes even less. The larger 5.9L version—which we're using here—is on the high end of that spectrum, and 5.2L cores can be had for as little as $100. Even if you have to go through two or three of them, the dollars pencil out about the same. At the end of the day, even if you have a pro do all the heavy lifting on an engine like ours, you're still buying a complete turnkey engine for less than the price of a bolt-on blower kit for a late-model Hemi. If you build it yourself, a good core and all the parts can be scored for around $4,000.

Cylinder Heads

The inspiration for our Budget Sledgehammer comes from EngineQuest's CH318B cylinder head. We detailed it in an earlier story [here], but in a nutshell these stock-appearing iron cylinder heads fix a number of problems inherent in the stock Magnum head, namely cracking and warping. When EngineQuest designed these heads for the reman market, they also endowed them with more flow and improved the pushrod pinch in the intake port. With a little work, these reman heads can outflow aluminum performance pieces. Companies like Hughes Engines and IMM Engines (who helped us with this build) have seized on that and brought their own versions to market, with our IMM-prepped pieces easily topping the 260 cfm mark at .600-inch lift.

To backtrack a little, the EngineQuest CH318B casting was designed to be used on a Magnum block, but it has the LA-series intake bolt pattern, so it can take any of the wonderful high-performance LA intakes (318/340/360) on the market. This increases the horsepower and keeps a cap on the cost. When IMM modifies the EQ heads, they open the valve pocket area, blend it into the throat, put a nice valve job on it, and put larger 2.02-inch intake valves in them. At $1,469 for a pair, it's easily the most expensive part of this build-up, but good heads are essential for making power. For those curious about using them with a Magnum intake, you'll be glad to know EngineQuest also offers the CH318A—an identical casting that retains the Magnum intake bolt pattern.


Pairing your cylinder heads with an intake manifold that's appropriate for the flow capability of the heads and the planned use is critical. This factory-based 5.9L Magnum is going in a 1973 Plymouth Duster that will see mostly street use with occasional drag action. Our 10.4:1 short-block, detailed in a previous story [here], has a Comp Mutha Thumpr hydraulic-roller camshaft with .556/.542 inches of lift (using 1.6 rockers) and 235/249 degrees of duration, ground on a 107-degree lobe separation angle. When talking about an engine for a hot street car, this is smack-dab in the middle of goldilocks territory. We'll be able to run on ordinary 91-octane pump gas without detonating, and the valve timing will provide enough flow to produce serious power without causing ill manners or bleeding off too much cylinder pressure.

Our compression, cylinder heads, and cam choice all point to using an intake manifold that will accentuate performance on the street with lots of off-idle grunt, a fat midrange, and a top-end that holds on until the limit of our modest valvetrain is reached—about 6,000 rpm. Going with anything bigger means spending a bunch more on everything from valvesprings and rockers, to big headers and a bigger fuel system. Mission creep is the biggest problem the DIY engine builder faces, so we firmly staked out our street territory with Edelbrock's Performer RPM AirGap intake. This piece is a third-generation dual-plane design that maximizes all the benefits of a dual-plane (wide powerband, good street manners, thermal management) while modestly stretching its capability into race territory.

While valvetrain options abound—including some very nice pieces from Hughes Engines which we plan to cover at a different time—we opted for a bare-bones approach here. Our cam lift being in the mid .500-inch range dictated the use of cost-effective beehive springs paired with 1.6 ratio Comp High-Energy roller rockers. We initially tried a ball-style rocker with a roller tip, but upgraded to the full rollerized High Energy rocker after discovering some binding. Fortunately, we were able to use a small-block Chevy part number, which kept the price in check. Likewise with the pushrods. Due to IMM's .035-inch longer Ferrea valves and the extra valve lift, we used a Ford-sized 6.900-inch chromoly pushrod, saving a little money there as well.


In the universe of carburetors there are many great choices. Chances are, you have several in your garage that you'll probably dust off for a build-up like this, but if you do decide to buy new, one of Quick Fuel Technology's Street-Q units would be a sound choice. The Street-Q series is chock full of racer features and comes in a bunch of sizes (650, 750, 850, and 950 cfm). They are unbelievably inexpensive (our 650cfm unit costs just $482), they're offered with either vacuum or mechanical secondaries, and have the full range of tuneabilty. Ours was almost perfect right out of the box, only needing a slight drop in primary jet size to get our air/fuel ratio right in the 12:1 sweet spot. By having a square bore footprint and a modular Holley 4150 architecture, it's easy to dive right into a QFT double-pumper. With high-end features like adjustable high-speed air bleeds, four-corner idle mixture, two-circuit metering, large sight glasses on the bowls, adjustable secondary linkage, and downleg boosters, even the serious racer will feel right at home with the Street-Q.


Driving our ignition system choice was a couple of things. Obviously, we wanted to keep the price down, but we also wanted a stock look. We arrived on the Pertronix Flame Thrower cast-look distributor for both of these reasons, but we also liked the fact that it had Pertronix's new Ignitor III ignition module mounted deep inside. This little jewel brings any vintage muscle car into the modern age with stuff like an adjustable digital rev limiter, multi-strike capability all the way up to redline, and five times more spark energy than a points system. Digging deeper, we liked the adaptive dwell, which like an HEI, expands the dwell time as rpm increases, meaning your coil will have plenty of juice—even at high rpm. It's a mean little distributor, and when paired with Pertronix's Flame Thrower III coil with 45,000 volts (at just 0.32 Ohms), makes for a power-packed combo. Carrying the sizzle to our NGK FR5 plugs was a set of universal 8.8mm Flame Thrower wires. All in, our Pertronix bill came to around $360, but given that we've seen marginal vintage ignitions cost as much as 50 hp on the dyno, it's a price we were willing to incur.


It's common practice for dyno operators to use the same set of headers on the dyno for the sake of simplicity. These are often large-diameter, long-tube step headers that easily clear the dyno apparatus, and that produce big numbers on the screen due to their optimized design. In practice, however, these dyno headers rarely fit into real cars like our 1973 Duster. For that reason, we ordered a set of Patriot 1 5/8-inch diameter long-tube headers with a block-hugging design (part No. H8206-1, $406.97 Summit). These are specifically for a Chrysler small-block being used in an A-Body, so their various twists and turns are designed to clear steering and suspension components without rubbing on sheetmetal. Being a long-tube design, they also boost horsepower and torque, widening the powerband in the process. An attractive ceramic metallic coating further ads to performance, and holds the inevitable corrosion at bay. We think the Patriot long-tubes were a good choice, producing nice power even though they weren't optimized for the dyno environment. The good news is that thanks to our Patriot long-tube headers, the numbers we got for the Budget Sledgehammer are representative of what we'll get once installed in our Duster.


With our long-block assembled, loaded on the dyno, and filled with Torco 10w30, Brian Hafliger of IMM Engines ran a tuning loop on the Budget Sledgehammer, adjusting the total timing to 34 degrees and making a minor adjustment to the primary jetting. With everything up to temp and checking out, it was time to make a full power pull, first optimized with the 650cfm Street-Q carb. We had our sights set on a solid 430 hp—about what a similar vintage Vortech small-block Chevy might produce with similar equipment. What we got was a solid 461 lb-ft. at 4,500 rpm and 454 hp at 5,800 rpm. The little Street-Q blew us away, so we were understandably eager to try the 750.

Typically, a larger carb on an engine equipped like ours would be worth 5 to 10 hp more at key points in the power curve, but once we had optimized our jetting for the bigger 750, it turned out not to be so. That said, the big double-pumper produced 465 lb-ft of torque at an even lower 4,400 rpm (+4 lb-ft.), and 455 hp (+1 hp) at the more elevated speed of 6,000 rpm. Average torque increased by 2 lb-ft and average power improved by just over 2 hp. That's pretty much a wash—not enough to really feel in the seat of your pants—but since the price difference is only $36, probably still worth the money.

Our big problem now? The Budget Sledgehammer has enough slam to break just about every part in our Duster's slant-six driveline, from the fragile factory 904 TorqueFlight, to the toothpick driveshaft and wimpy 7.5-inch rearend. We have some serious updating to do before we drop it in and bolt up some slicks, so stay tuned as we get underway with more wrenching on our Duster!

Dyno Results

5.9L Magnum Small-Block

QFT 650cfm CarbQFT 750cfm Carb

Read More!

Find out how we got this far in our 5.9L Budget Sledgehammer Magnum small-block build-up with these two previous stories!

EngineQuest CH318B cylinder head build-up and flow test:

Make Big-Power Magnum 5 9l Mopar Heads

IMM Engines short-block build-up of 5.9L Magnum donor engine:

Build 500hp Capable 360 Magnum Short Block Cheap


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