You may or may not know all of the details about Chrysler’s latest version of the Hemi engine, but one thing is certain: This engine is a performance powerhouse. Even in stock form, the late-model 5.7, 6.1, 392, and 6.4 Hemi engines will run circles around past versions of this venerable powerplant in terms of power and efficiency, and the new Hemi platform responds great to modifications as well. So when it came time to choose an engine platform for the ’10 Dodge Challenger we’re building as a dedicated drag racing car, the late-model Hemi just made the best sense. This month we’ll show you what parts we utilized to build our 426-inch short-block, and next month we’ll finish the build with a full description of the top end and dyno testing. If you’re a fan of the new Hemi, then you’ll definitely want to follow this build as our results were impressive. And if you’re not a fan, well this pump-gas late-model Hemi may just convince you that you should be.
If you compare the late-model Chrysler Hemi (or third generation Hemi) to the first Hemi engines or even the famous second-generation 426 Hemi built during the ’60s and ’70s, the newest version wins in every category. No matter if comparing power per cubic inch, average power, peak torque and horsepower, efficiency, or weight, the newest Hemi engines simply outperform all of the past versions hands down. Another advantage to the third generation Hemi engine is that contrary to the somewhat rare first and second generation Elephants, these engines are plentiful and inexpensive.
Unlike the second generation Hemi which was a rarely-selected optional engine only available in select models, late-model versions are widely produced and served as the base V-8 engine in hundreds of thousands of cars and trucks produced by the Chrysler Corporation during the past decade. So with more and more of these cars accumulating high mileage and succumbing to accidents, finding a late-model Hemi in the local scrap yard or from a core supplier is a fairly easy and inexpensive proposition. In fact, we know of several enthusiasts who have purchased running 5.7 liter Hemis locally here in Florida for less than a thousand bucks. Bare blocks, cranks, cylinder heads, and other parts are also available directly from any Chrysler or Dodge parts dealer, so if you don’t want to bother with a used engine you still have the option of building one with new parts.
Even better, aftermarket companies like Indy Cylinder Head, Comp Cams, Callies Crankshafts, Milodon, and many others already support the late-model Hemi with a great variety of aftermarket parts to make these engines really perform. Since our latest project car is a ’10 Challenger that will be dedicated to bracket racing, we decided a third generation Hemi engine made perfect sense to power our car. And with current pump gas prices approaching what we paid for racing fuel in the not-so-distant past, we made the decision that this engine would have to run on pump gasoline with an octane rating of 93. With these factors in mind, we assimilated a list of parts that would result in a powerful 426 cubic inch late-model Hemi, which we could fuel up at the local gas station.
The first step in our process was to choose the appropriate parts for the short-block of this engine. Our choices were limited to the 5.7 and 6.1 blocks due to availability, and the differences in these blocks are minor but significant. The 5.7 Hemi utilizes a 3.920-inch bore size combined with a 3.58-inch stroke, while the 6.1 Hemi’s bore size is 4.060 inches with the same 3.58-inch stroke. Since the 6.1 block has larger diameter bores, as well as reinforced bulkheads, we chose this block as the foundation for our late-model 426.
All late-model Hemi blocks are hybrids of sorts, using both standard and metric hardware in various locations. For this reason, it really helps to have a core engine around when considering a build like this. Since we built our engine at the Indy Cylinder Head facility in Indianapolis, Indiana, we had the luxury of their supply of hardware and parts. If you’re going to build a new Hemi in your garage or have your local machinist perform the work, be sure to not throw out any of the hardware, fittings, or pipe plugs as they might be difficult to replace at the local hardware store. For our build, we utilized a new 6.1 block, and Indy’s full service machine shop prepped the block for our stroker application.
To achieve a displacement of 426-inches (or 425.67928 to be exact), we utilized a bore size of 4.090 inches and a stroke of 4.050 inches. The 6.1 block can be bored to this dimension with plenty of cylinder wall left, and to fit our stroke we only needed to cut small provisions for the connecting rods at the bottom of the cylinders. Other block modifications include chamfering the inside of the provision for the oil filter, blocking off the MDS provisions, and installing one-piece grooved camshaft bearings to replace the factory two-piece units.
As a foundation for the rotating assembly of this engine, a forged crankshaft from Callies’ Compstar line was utilized with the required stroke of 4.050 inches. This cranksahft is manufactured from 4340 steel, features standard small 2.200 inch (commonly known as small-block Chevy rod journal size) journals, and has gun-drilled main journals to save weight. The Compstar crankshaft is also double keyed, and comes with a forged steel reluctor wheel to replace the brittle factory wheel for the crankshaft trigger. Compstar 6.125-inch length forged H-beam connecting rods were combined with Diamond forged flat-top pistons to give us the pump-gas friendly 10.85:1 compression we were shooting for. The Diamond pistons are lightweight, utilize a .927 inch diameter piston pin, and metric rings for reduced internal friction.
Camshaft selection in an engine like this is critical, and we chose to stay with a hydraulic roller since the late-model Hemi comes standard with this type of cam. We had a good idea of the cam we wanted for this engine, and calling Comp’s helpline verified we were on the right track. Knowing late-model Hemis like a wide lobe separation angle, we chose a hydraulic roller cam with a lobe separation of 114 degrees. This cam features .584-inch intake and .579-inch exhaust lift, and 242 and 248 degrees duration at .050 inch lift respectively. This cam, along with a set of factory hydraulic roller lifters, will give our engine plenty of midrange torque and high end power, and should provide peak power at or just below 7,000 rpm. Since the camshaft is oiled last in the late-model Hemi, plenty of cam lube is required when assembling one of these engines.
To drive the camshaft, we chose a Manley double-roller, adjustable timing set. Unlike conventional Mopar V-8 engines, the timing marks on the late-model Hemi line up at the top of the cam gear, and the bottom of the crank gear, for proper cam timing. Additionally, the oil pump is driven by the crankshaft, so when using the wider double-roller timing set, special oil pump spacers are required and provided with the Manley timing set. We verified cam timing with a degree wheel, and utilized the provisions on the Manley timing set to make necessary adjustments before installing our Melling oil pump.
Late-model Hemi engine oiling is critical, especially since the engine oils the valvetrain first, and then the bottom end. To provide the necessary lubrication to this engine, we called on Milodon since they have a race specific oil system for the late-model Hemi. Designed around the Challenger Drag Pak Stock Eliminator platform, the Milodon oiling system utilizes a rear sump oil pan and pickup, along with a windage tray that doubles as a crank scraper for great oil control. The late-model Hemi already has one of the best oil return designs of any Chrysler engine, and combined with the Milodon components proper oiling and scavenging of oil will be ensured.
Having assembled plenty of high-performance Mopar engines over the years, this author was fortunate for the opportunity to build this late-model race Hemi with the guidance of Indy’s top engine builder, Ken Lazzeri. While the late-model Hemi is similar in many ways to early Mopar engines, there are a number of variances that make assembly different from earlier Mopar engines. The main bearing notches are opposite from each other rather than on the same side, which is the way BMW and Mercedes engines are and tells you a bit about the heritage of the late-model Hemi. The thrust bearing is also a separate piece, not attached to the main bearing, and is only one half circumference of the thrust provision of the crankshaft. The timing gears and chain system are different as well, utilizing a tensioner to keep the chain engaged on the gears properly. The late-model Hemi also requires thinner oil viscosity due to the lifter, pump, and oil pressure relief valve design.
We’ve learned a lot building the short-block for our 426-inch late-model race engine, and can tell you firsthand that you’ll be surprised at the power numbers this engine makes. Next month we’ll discuss the cylinder heads, induction, and ignition system of this Hemi, and show you the results we achieved on Indy’s engine dyno. You won’t want to miss part two of this build, and be sure to visit Mopar Muscle to see video footage of this powerful Hemi running on the dyno.