We'd all love to install a high-horsepower engine in our Mopar, and many of us do modify our engines with aftermarket parts in the quest for more power. In fact, there's never been a better time to be a Mopar lover, as the market is flush with the reproduction parts needed to make your car even better than it was when the first owner picked it up from the dealership. One area of our hobby that technology has really helped advance is our car's engines. Nearly all the parts, including engine blocks and aftermarket cylinder heads, are available for most Mopar applications, allowing us to build engines of larger displacement, and far more power than our cars came with from the factory. But because our older Mopars were only designed to handle a maximum of 425 horsepower, there are some upgrades that must be performed to the car before installing that big engine.
A few issues ago, we built a low deck, 451 stroker for our '71 Road Runner, attempting to make as much power as possible on pump gas, while sticking to a "reasonable" budget. While we did spend money where it counts on this build, specifically the 440-1 aluminum heads from Indy Cylinder Head and roller cam and lifters from Comp Cams, we also conserved money by purchasing our cylinder heads in kit form, using a factory block and crankshaft, and choosing reasonably-priced forged pistons and rods from 440 Source. We also had the machine work done locally at Auto Performance Engines, and we assembled this engine ourselves instead of paying someone else to do it.
Clearly this is not the least expensive engine we could build, as a stock 318 would have satisfied that requirement, but our purpose was to show you how to make big power on pump gas with a normally aspirated big-block. We certainly could have added to our expenses by building a larger displacement engine with expensive billet internals and block, using race specific rocker arms, a belt drive for the cam, and expensive dry sump or external pickup oil system. We stayed away from these parts as the benefits they provide exceed what is necessary to make plenty of power for the average street car. In fact, this engine will require that our Road Runner be modified not only so the fuel, ignition, and cooling systems can adequately support the more powerful engine, but in the interest of safety as well.
This 451-inch big-block is far more powerful than the 383 our car came with, and will have more torque and horsepower than our 40-year-old car was designed to handle. For this reason, we felt it necessary to perform some modifications to our B-Body both before and while we were installing the new engine. In earlier issues of Mopar Muscle, we rebuilt our car's suspension with components from Performance Suspension Technology (PST) and installed front disc brakes from the same company. While we were at it, we also installed a larger diameter front sway bar and a rear sway bar from PST as well. Our 8-3/4-inch differential was also modified with a new 3.55 Sure Grip centersection from Randy's Ring and Pinion. This month, we'll show you what else we deemed necessary not just to make our car able to safely hold the new engine's power, but also to ensure the engine performs up to its potential.
Starting with the basics, fuel and ignition, we modified our Road Runner's fuel system with new 3/8-inch aluminum fuel line, and a Holley fuel pump and regulator. Sticking with our budget theme, we made the fuel line ourselves with a roll of tubing we got from a local race shop, and used a fuel pump and regulator we had in our spare race parts selection. To provide the extra ignition energy needed to power a high-performance big-block and to provide rev-limiting protection, we chose MSD's Digital 6 Plus ignition box. This ignition, along with an MSD Pro-Billet distributor, coil, and ignition wires, not only supplies the required additional spark energy, it also allows us to easily set two different levels of engine rev-limiting and gives us the option of retarding the ignition timing in case we ever chose to add nitrous oxide to our engine (not that it needs it).
To keep our high-performance engine cool, we knew it would be necessary to upgrade our radiator and cooling system as well. First, we replaced our car's original radiator with an aluminum replacement from Wizard Cooling. Wizard offers bolt-in replacement radiators for most Mopar body and engine combinations, and their radiators are a down-flow design just like the originals. Additionally, Wizard offers radiator and fan combinations, and we chose their kit that included two electric fans and custom fabricated aluminum fan shroud. To pump the coolant, a Mopar aluminum water pump housing was utilized along with a Milodon aluminum high-volume water pump and 160-degree thermostat.
With the engine taken care of, we moved on to the car itself, knowing that our factory style clutch and stock axles simply wouldn't be up to the task of handling our engine's additional torque. A clutch disc failure is no laughing matter, and a broken axle can at best leave you stranded, or at worst wreck your Mopar. With a quick call to Centerforce, we had a new DFX clutch, pressure plate, and SFI approved flywheel on the way, along with an input shaft bearing in lieu of a stock style bushing. Randy's Ring and Pinion provided our forged Yukon axles, and we cut them to length ourselves before installing new sealed axle bearings. We also considered sub-frame connectors necessary for a car with this kind of power, so we ordered a pair of bolt-in connectors from Competition Engineering.
While we could have gone over the top with this build in terms of the equipment needed to make this combination work, we decided instead to stick with the basics and only install the minimum equipment to ensure our engine would run properly and wouldn't destroy other parts of our Road Runner. We plan to mostly drive this car on the street but plan to take it to the strip as well to see how it performs. Our hope is that it will be quick enough we'll need to install other equipment like a driveshaft loop, safety harnesses, and possibly even a rollbar to make it legal at NHRA tracks. If we achieve our goal, we'll cover the additional safety installations in future issues. Be sure to go to our website, www.moparmusclemagazine.com, where we'll post video of our dragstrip testing.
