The engine featured here belongs to an '86 Corvette and sports a 383ci displacement, ported Dart Pro1 200cc cylinder heads, a Lingenfelter 219 single-pattern hydraulic roller camshaft (219-/219-degree duration and 0.560-/0.560-inch lift with 1.6 rockers), and Lingenfelter 1 3/4-inch long-tube headers dumping into a stock diameter 3-inch Y-pipe and a Magnaflow 2.5-inch exhaust. The car is street driven but spends a great deal of its time on the autocross course, where low-rpm torque is very important. Since the current output of 430 rwtq already overwhelms the car's 315/35-17 Kumho Victoracer race tires, we weren't too concerned about potentially sacrificing a small amount of low-end thrust in exchange for a wider powerband.
This particular SuperRam has stock runners (above) and plenum but features a heavily massaged base and a larger-than-stock 52mm throttle body. By contrast, the Pro-Flo XT will be bolted on with no porting or port-matching. While the casting is quite good, there's still plenty of material to clean up in the runners if one were so inclined. Port matching the runner exit to the appropriate gasket size would yield an approximately 20 percent increase in cross-sectional area and would increase airflow as well.
We chose an Edelbrock 90mm throttle body to match the Pro-Flo XT's 90mm inlet. It's also worth noting that our test engine was running a custom dyno tune that was optimized for the SuperRam combination. We didn't have a chance to retune the PCM for the new intake before testing, so you can assume there's more left in this combination. Our dyno session was carried out at Duke's Auto in Umatilla, Oregon. You may have heard of the owner, Duke Langley, as he campaigns an '89 Corvette nationally in SCCA Solo racing. Langley strapped the Vette onto his Dynacom dynamometer to record our before and after runs.
We removed the SuperRam intake using a 1/4-inch gear wrench and a long Allen ball-head driver on the runner-to-base bolts. (Replacing the original Torx bolts with Allen heads is also a great idea.) To ease installation, we had previously slotted the small bolts connecting the runners to the plenum. If you ever plan on installing or uninstalling a SuperRam, these tricks are a must.
After removing the SuperRam, we went to work on installing the Pro Flo XT. Compared with installing the five-piece ACCEL intake, the Pro Flo XT is a breeze. However, as the manifold is not designed as a direct replacement for the C4 Corvette, special care has to be taken on certain parts of the swap.
While we utilized braided lines, we could have saved a good deal of money using either flared hard lines or push-on style hoses. If you do decide to go the braided route, you'll save yourself a lot of time and several bloody fingers by picking up a Koul Tool assembly tool like the one shown here.
We also installed a stand-alone -6 AN bypass EFI fuel-pressure regulator to manage fuel delivery. In hindsight, it would have been better to use a smaller EFI regulator or a remote-mount unit, as we had to do a very slight amount of grinding on the corner of the Pro-Flo XT (above) to prevent interference. While we didn't utilize the tapped NPT hole in that corner, it would have worked well for routing a vacuum line straight to the brake booster.
The injectors are LS1 25-lb/hr (at 43.5 psi) units and require the use of mounting tabs (included with the kit) to locate the fuel rail at the correct height and angle. Our setup, with fuel feeding both rails at the front of the manifold, just barely fits.
We had previously installed an MSD small-cap HEI distributor (for '87-'92 GM F-bodies) to make timing changes with the SuperRam easier. If you're not already running a small-cap HEI unit, you'll need to get one to use with the Pro-Flo XT.