For this junkyard turbo article, we decided to serve up a little bit of everything, starting with bolt-on boost to an otherwise stock Hemi motor. In our case, that stock motor was a '06 Hemi 5.7 from Dodge. Sporting the most recognizable performance name in the industry, the modern Hemi 5.7 had some big shoes to fill!
Perhaps overshadowed by the bowtie boys, the modern Hemi suffers only from a PR problem, as they offer every bit as much performance as their GM counterparts. Like the LS, both the 5.7L and 6.1L were blessed with impressive heads. The head flow allows the Hemi 5.7 to respond very well to even mild cam upgrades. Think of the modern Hemi as a motor equipped with race heads and a stock camshaft. Owners of small block (and some big block) Dodge motors would love the flow numbers offered by even stock Hemi heads, let alone ported versions (see the flow numbers in "Inside the G3 Cylinder Head," Oct. '12).
The boost came from HP Performance in Roswell, New Mexico, in the form of a single turbo kit. The kit was designed to bolt directly to the factory SRT8 exhaust manifolds and provide 7 psi of boost to the stock motor. The boost on this application was limited by the stock internal components of the motor and not the potential of the kit itself. As we will see in the second test, the kit offered exceptional performance on a dedicated application.
Junkyard Turbo
Impressed as we were with the result of adding boost to the stock motor, we decided to take things to the next level and really push the parts. To do this, we first needed a dedicated test motor, something that would withstand the rigors of elevated boost and power levels. Knowing that Hemi 5.7 truck motors are now becoming more common in wrecking yards, and that they make for impressive swap candidates in early Mopars, we decided to head off in that direction with our boost builder. After securing a Hemi 5.7 core motor, we tore it down and shipped it off to L&R Automotive for machining and prep for the Scat stroker kit. Though available and less expensive than the more desirable 6.1L, the displacement of the 5.7L was limited by the smaller bore size (3.917 versus 4.055). To increase the displacement, we increased the bore slightly (from 3.917 to 3.937) and installed a 3.795-inch Scat stroker crank (up from 3.58). The combination netted us a 6.1L-matching 370 cubic inches from our 5.7L junkyard turbo.
The forged steel Scat crank and 6.125-inch, 4340 rods were combined with a set of 0.020-over Probe Pistons. The pistons featured a 10cc dome to put the static compression ratio just under 10.0:1-a good compromise that would allow plenty of power in both normally aspirated and turbocharged trim. The assembled short-block was topped off with a set of ported 5.7L heads from Total Engine Airflow (TEA). Shipping our heads to TEA resulted in an increase in airflow from near 260 cfm to 315 cfm-more than sufficient to support our intended power levels. The stock valves were retained, but the heads were further upgraded with a set of 26918 valve springs and matching retainers from Comp Cams. The heads were secured using ARP head studs and Fel Pro MLS head gaskets. We selected a cam that promised to work well both in normally aspirated and turbocharged trim. The custom Comp hydraulic roller offered 0.589 lift (both intake and exhaust), a 239/247-degree duration split and a 114-degree LSA. The cam on our junkyard turbo was installed with the factory MDS lifters (though non-MDS lifters would be a better choice due to reduced weight).
Fresh from the junkyard the Hemi was rebuilt and shuffled to Westech Performance for some hits on the dyno.
Finishing off the stroker Hemi was a Milodon oil pan, pick up and windage tray combined with a new (factory) oil pump. Prior to the installation of the pump, we installed a double roller timing chain from Comp Cams that included the necessary spacers for oil pump clearance. On the induction side, we installed an aluminum SRT8 intake manifold and stock throttle body. The drive-by-wire throttle body was converted to manual (dyno) use by welding a shaft and rotator in place. It was also necessary to mill the front cover (it was from a truck application) to provide adequate clearance for the front-mounted throttle body (better to get a core or front cover from a car application). In anticipation of the expected power levels, we replaced the factory injectors with a set of 75-pounders. Tuning was provided by the Fast XFI/XIM management system and factory coil packs. Unfortunately we had no Hemi headers available for testing, so we were forced to run our normally aspirated test with a set of factory SRT8 exhaust manifolds feeding 2.5-inch collector extensions. Dedicated long-tube headers would likely increase the power output by 15-17 hp over the stock manifolds. The final step was to fill the crankcase with break-in oil from Lucas, and we were ready to roll.
The Hemi was dialed in using the XFI/XIM engine management from FAST. It can control both the coils and the fuel injection independently or together using either a drive by wire or cable throttle body.
After a computer-controlled break-in procedure, the normally aspirated Hemi was run in anger. Tuned by Westech's Ernie Mena, the stroker Hemi responded with peak numbers of 523 hp at 6,700 rpm and 456 lb-ft at 5,500 rpm. Torque production from the 370-inch Hemi exceeded 425 lb-ft from 4,300 rpm to 6,300 rpm. Now we were ready for some boost. On went the turbo kit from HP Performance, bolting directly to the factory SRT8 exhaust. The kit included an air-to-water intercooler, a turbo capable of supporting over 700 hp and the necessary plumbing to direct all that wonderful boost into our awaiting Hemi. After hooking up the plumbing, we were rewarded with 765 hp and 764 lb-ft at 8.8 psi of boost. Torque production exceeded 700 lb-ft even down at 3,500 rpm (the starting rpm for our dyno pulls) and carried this value all the way out to 5,600 rpm. Those were some impressive numbers considering the modest boost level and the fact that the small turbo from CX Racing was nearly out of steam.
Since the idea was to put the turbo kit from HP Performance to the ultimate test, we decided to step up in turbo size. The 76mm unit from Precision Turbo represented a huge jump in both power and price compared to the smaller unit from CX Racing. Sized to feed four-digit power levels, the Precision turbo would surely demonstrate whether the rest of the kit from HP Performance was up to snuff. Running dyno water through the massive air-to-air intercooler core (ice water would add even more power), the Precision turbo cranked out a peak boost pressure of 16.5 psi and easily topped the 1,000hp mark. The best numbers of the day were 1,051 hp and 915 lb-ft of torque. The stroker not only survived the abuse, but thrived and was ready for even more. Having successfully reached our goal of 1,000 hp and demonstrated the merits of the Hemi Helper turbo kit from HP Performance (to say nothing of the power potential of a turbo Hemi), we packed it in and called it a day.
Prior to the installation of the turbo kit from HP Performance, the 5.7L stroker was treated to a couple of break-in cycles before being tested in normally aspirated trim. Running Lucas 5W-30 oil and SRT8 exhaust manifolds the Hemi produced 523 hp and 456 lb-ft of torque. Torque production exceeded 425 lb-ft from 4,300 rpm to 6,300 rpm.
Parts List
* Provided with kit
** Base kits
+ Price from www.summitracing.com
Scat 5.7L Hemi Stroker-NA vs. CX Racing Turbo-8.8 PSI The power curves illustrate two very important points, the first of which is the fact that our 5.7L Hemi stroker was no slouch in normally aspirated trim. Offering 523 hp and 456 lb-ft of torque, the 370-inch (6.1L) Hemi was plenty potent. Adding 8.8 psi of boost from the CX Racing turbo and HP Performance turbo kit improved things substantially. The Hemi Helper pushed the power numbers to 765 hp and 764 lb-ft of torque.
SCAT 5.7L Hemi Stroker-NA vs. Precision Turbo-16.3 PSI Sized for street boost levels on a stock motor, we knew we had to step up from the turbo from CX Racing to an even larger unit. Precision Turbo came through with our four-digit turbo by providing a 76mm unit of their own with a larger turbine and AR ratio. Running 16.4 psi, the turbo Hemi pumped out 1051 hp and 915 lb-ft of torque. If there is one thing better than a Hemi-it's a turbo Hemi!
At just over 16 psi, the Precision Turbo produced 1,051 hp, with at a little more power left in reserve. Since we officially exceeded our goal of 1,000 hp with two of the turbos, we saw no reason to get greedy and crank up the boost beyond that point.
