Just uttering the word “hemi” conjures the feeling of growling exhaust, the smell of hi-test gasoline, and classic Mopar iron hanging the wheels through the 60-foot mark. Every American knows what a HEMI is, whether they are a gearhead or not, it is an icon of the horsepower-fueled 1960s and 70s. The modern version of the HEMI has been around since 2003, with one major change in 2009 when they added MDS, which is Chrysler’s multiple displacement system with variable valve timing. As far as a stock application, the HEMI is a very capable and powerful engine. Start adding performance parts to it, however, and things can quickly spiral out of control.
Our project begins with a 2009 Dodge Challenger that had been heavily modified by the previous owner. The car had some issues and the new owner brought it to Red Dirt Rodz for a tune up. The 5.7 HEMI had a Procharger with a custom-ground camshaft and only 27k miles on the odometer. The main concerns were: the engine revs itself after disengaging the clutch, and 2nd and 3rd gear would grind. The plan was to take the car to the chassis dyno for a tune before tackling the transmission issue. We took the car to D&G Dyno in Hennessey, OK, and put it on the rollers. We believed that most of the run issues were in the tune, as the Chrysler software has some unique parameters that are really easy to get wrong. The first pull made 525 horsepower at the rear wheels, which translates into about 600 at the flywheel.
A look into the tune showed some significant concerns with the tune. The previous tuner added 12 degrees of timing, which will make a lot of power, but does so at the risk of detonation. We pulled the timing out of the tune, made some adjustments, and fired up the motor for another run. As soon as the starter kicked in, the death rattle began. We loaded the car back on the trailer and took it back to the shop for inspection. We pulled the spark plugs and two of the cylinders had evidence of piston damage, which was confirmed by the porcelains of 3 plugs being severely damaged. Time for an overhaul.
Why did this happen?
The added timing is only part of the problem, the real meat of this issue boils down to the parts inside the 5.7 HEMI. These engines are really good in stock form, but as soon as you start adding power, especially boost, they begin to fail in several key areas.
Pistons- The stock pistons in all of the HEMIs are cast; just regular old cast pistons, which does not respond well to added combustion pressures. Additionally, the rings are very thin and the top ring land is positioned very high on the piston, making the piston even more brittle around the edge. At any power level with boost, the top of the ring land can break off, leaving the pieces to bounce around inside the combustion chamber. This is what happened inside our 5.7. One piston showed signs of being broken for quite a while, while the other piston was a fresh break.
Crankshaft- The 6.1 HEMI has a forged crank, which is plenty strong enough for anything you want to do. The 5.7, however, comes from the factory with a cast crank that bends at the 600-hp level. Because this engine was making over 600 horsepower with one damaged cylinder, this engine would not have lasted much longer on the street. The 6.1 crank fits into the 5.7 block without any mods.
Bearings- Another way that Chrysler cheaped-out on the HEMI is with the main and rod bearings. The new HEMI uses bi-metal aluminum bearings. While these are good for plain-jane stock low-performance engines, performance engines are much better off with tri-metal bearings. The issue with the bi-metal bearings is that they melt. Our 5.7 had one main bearing that was wiped out and had seized to the crank, it spun freely in the block. This could be evidence of the crank bending as well.
Connecting rods- While the rods inside the 5.7 were in good shape, they are only good to about 600 horsepower. This is just one more way this engine was truly a ticking time bomb.
These are the inherent issues with the 5.7 HEMI engines that most performance builders will face. In the end, if you plan to supercharge your HEMI, you need to stay on the low-boost side and run a conservative tune, otherwise you are guaranteed to be facing a complete build in short order.
Aside from the seriously aggressive tune, and the busted pistons, we also found several other significant issues inside the motor. The cam had been swapped out for a custom-ground bumpstick from Crower. While this helped take advantage of the blower, it created some clearance issues. The previous builder obviously did not check the piston to valve clearance. All 8 exhaust valves were hitting the pistons at TDC, leaving indention marks and all 8 valves were bent. Additionally, the intake valves had been replaced with 2.02” valves (stock is 2.0”), without addressing the valve seats or port of the head, which defeats the purpose of larger valves.
The Build Plan
At this point, we knew we had to do a complete build on the engine if it was to survive life on the street. The 6.1 stock forged crank would be a suitable solution to the cast crank issue, but if you are going to spend money of parts, you might as well go full-bore and step it up, which is what we decided to do in the way of 392 cubic inches of HEMI grunt. We selected a SCAT forged steel crank, and coupled it with a set of their 6.125” H-beam rods. When ordering these cranks, you have to be careful with your selection. Because all of the cranks fit both the 5.7 and the 6.1 blocks, you can end up with the wrong crank. The 426 stroker crank for the 6.1 block is 392ci in the 5.7, this is what we selected. To handle the abuse of the boost, we picked up a set of Mahle pistons in .010” overbore.
We are retaining the custom cam (Crower 259-degrees & .559” lift intake, 267-degrees and .581” lift exh, 111 lobe center), stock intake, rocker arms, exhaust, and of course the procharger. We upgraded to a BBK big mouth throttle body, and added a set of Detschwerks fuel injectors.
If there is anything to be stressed in this article, it is that the key to building a modern HEMI is research. There is very little information available on rebuilding the 2009-up versions, and there are some significant differences that you need to know about. These are all related to the MDS/VVT system.
Timing chain- The non-MDS/VVT engines have a double-roller timing chain, but the 2009-up engine with MDS only have a single roller, and there is not room to add a double-roller. This created some problems for 5.7 powered vehicles when coupled with the automatic transmission. After 28-30k miles, the timing chain breaks, destroying the internals of the engine. There was a recall over this, and part of the fix was a nylon chain guide. The issue is how the MDS system works, which binds up the chain and it breaks. Manual-shifted cars do not seem to have this issue.
Crankshaft- The 2009-later factory cranks hve an extended flare for the crank gear. If you buy an aftermarket crank (which fit all the HEMI blocks), you will discover this when you are installing the timing chain. The crank gear will not sit flush on the base of the crank, rather it will float, which is not going to work. You need a spacer, which slides onto the crank snout. These are available for $25 from ShopHemi.com. Additionally, you will need the correct reluctor wheel for the crankshaft position sensor. There are two wheels for 2009-2012 5.7 and 6.1 HEMIs, they both have the same 58-tooth count, but the 5.7 is a 3-bolt pattern, and the 6.1 has 4-bolts. Most aftermarket cranks use the 4-bolt wheel. 2008 cranks use 32-tooth reluctors (same bolt pattern difference between the 5.7 and 6.1), while the 2013-up use a different 58-tooth wheel. You must make sure you have the correct wheel. We purchased a new 4-bolt 58-tooth wheel from Molnar Technologies.
Cam bearings- The VVT camshaft has a double-wide front journal; a non-vvt cam will not work along with non-VVT cam bearings. The stock bearings are 2-piece units, and a real bear to remove and install. We used a long punch to collapse the front bearing and pull it out. The rest were removed using the normal operation of the cam-bearing tool.
The machine work was handled by Boyd’s Machine in Norman, OK. The block was bored .010”, because the factory bore on the 5.7 tends to be more oval than round. We had it line-bored while we were at it. The rotating assembly was balanced and set checked for proper clearances. The stock cylinder heads were cleaned up, new exhaust valves installed, with a multi-angle valve job and a little minor port work for the 2.02” intake valves.
With the parts back in the shop, we yanked the cam bearings out, which turned into another headache. The front cam bearing had to be collapsed to get it out. They are 2-piece bearings, and the way the block is cast means there is no place to tighten the cam tool inside the bearing. Each bearing is slightly smaller than the preceding, from front to back, so you start with the rear-most bearing, and work towards the front when installing new bearings. Before installing the new bearings, the block was washed with hot soapy water and all the passages were brushed out to ensure any debris from machining was removed.
Installing the rotating assembly is pretty basic, just like any other engine. We used file-fit rings from Mahle, which were opened up a little extra to compensate for the additional expansion to be expected with a boosted engine. File-fitting requires a little bit of patience, but it is the only way to get the proper fit. The pistons use floating pins with circlips, so you can assemble them in the shop without heating the rods or using a press. The bearings are all high-performance Clevite pieces. Holding all of that weight slinging around at 6,000 RPM, are a set of ARP main studs, head studs, and ARP2000 rod bolts. We used a combination of factory bolts and ARP fasteners for the remaining pieces.
There are a few key components that you must remember when building a modern HEMI. First, there are 4 dart-shaped magnets that go into to oil galleys above the lifters. MDS-enabled engines use valves in these ports, but the non-MDS engines have nylon plugs. These plugs are o-ring sealed and hard to get in and out for cleaning, so be careful.
The second issue is the oil pan bolts. Chrysler specifies a very complex 3-increment torque procedure that must be followed; otherwise the cast aluminum pan can crack. This is not the typical center-out sequence, it is a little convoluted, but this is the spec from Chrysler. You must use new bolts, as the originals are torque to yield and not reusable. Here is the sequence, direct from the Chrysler manual:
“Align the rear of the oil pan with the rear face of the engine block and install the M10 and M6 oil pan fasteners finger tight. Using the following torque sequence, torque the M6 mounting bolts to 44 in.lbs.
Using the following torque sequence, torque the M10 oil pan fasteners to 39 ft.lbs. Using the following torque sequence, torque the M6 oil pan fasteners to 106 in.lbs.”
With the engine assembled, and back into the Challenger, we fired it up for a 20-minute break in. We used Royal Purple Break-In oil to ensure that there was plenty of ZDDP to protect the fresh metal. After the break-in period, we drove the car for about 300 miles before taking it to the dyno. This was to ensure that the rings had time to seat and that there were no issues with the engine. Once again, we took the car to D&G dyno in Hennessey, OK and strapped it to the rollers. We spent a full day adjusting the tables and building the right tune for the engine. The end results were an astounding 547 hp and 519 ft lbs of torque at the wheels as tested in the middle of August when ambient temps were in the 100s. The original dyno session took place in February in 45-degree weather. The tune on the Challenger is a very safe, conservative tune that will ensure long life and performance. In cooler temps, this tune should be good for 600+ at the wheels; hopefully we can revisit this when the temps cool down for a better “apples to apples” comparison. As it is, 550 RWHP is in the Hellcat zone for sure, and with the new forged internals, this 392 should provide years of brutal street fun.