When building a motor to maximize torque production, bigger is always better.
Back in Part 1 of our Cam the Ram series on the 5.7L Hemi, we subjected the bone-stock test motor to a simple cam swap. The wrecking yard motor was run on the engine dyno using a Fast XFI/XIM management system in two configurations, first with the stock cam, then with a mild Comp cam. Equipped with the stock cam, the 5.7L produced 370 hp and 407 lb-ft of torque. These numbers jumped to 401 hp and 427 lb-ft with the installation of the 260H-13 Comp Cam. The cam not only improved the peak power numbers, but offered consistent gains through most of the rev range with no loss in low-speed torque. Hot off the success of camming our Ram, we decided to take things to the next level. Looking to continue the theme of impressive torque production without sacrificing drivability, we elected the tried and true method of increased displacement. Basically we’re adding inches to get pounds—foot-pounds of torque.
1. The 5.7L Hemi stroker featured a forged crank, rods and pistons from Scat to produce a
As much as we hated the thought of tearing into a perfectly good running Hemi, out came the wrenches and sparks began to fly. The 5.7L was disassembled and sent over to L&R Automotive for machining and assembly. To increase the displacement, Scat Enterprises helped us out with a stroker assembly designed specifically for the 5.7L Hemi. Unlike the larger 6.1L, the displacement of the 5.7L was limited by a combination of the small bore size and the ability to dramatically increase it. The majority of the additional displacement came from increasing the stroke from 3.578-inches to 3.795-inches. Even larger stroker cranks are available for the 5.7L block but cost and complexity increase with displacement. The combination of the 3.795-inch stroker crank and 3.937-inch (.020-over) bore resulted in a final displacement of just under 370 ci. This combination nearly matched the displacement of the larger 6.1L, but with a different bore/stroke combination (the 6.1L combined the stock 3.578-inch stroke with a 4.055 bore). In addition to the hike in displacement, the forged rotating assembly provided a bulletproof short-block that was capable of withstanding some serious punishment.
2. L&R Engines was responsible for the machine work and assembly of the short-block. To en
The Scat and Probe crank, rods, and pistons were combined with a set of new rings from Total Seal, and bearings. To get things started, we installed the 260H-13 cam on the 5.7L, but don’t worry, we had a wilder cam waiting in the wings. The cam was installed using new cam bearings, but we elected to reuse the factory lifters, despite the 5.7L being equipped with MDS and our intention of eventually running a high-lift, long-duration cam. In addition to the cam, Comp Cams also supplied a new double-roller timing chain—an important component on a motor that eventually made power all the way to 7,000 rpm. To feed our newfound displacement, we elected to have the stock 5.7L Hemi heads ported by the flow experts at Total Engine Airflow. The stock heads already offered sufficient airflow to support more than 525 hp, but when searching for added performance, more flow is always a good idea. Besides, the ported head might support the additional power we have planned for the future. Porting the heads improved the flow rate by more than 50 cfm, bringing the intake flow from 260 cfm to nearly 320 cfm. The exhaust flow improved by just more than 35 cfm to 205 cfm (both measurements at .600 lift). The heads were secured to the stroker short-block using ARP head studs and Fel Pro MLS head gaskets.
3. The MDS lifters require use of the MDS-specific retainers (guides). Note the MDS guides
4. To illustrate the gains offered by the stroker motor, we installed the same 260H-13 Com
5. In addition to the cam, Comp Cams also supplied the necessary double-roller timing chai