Words And Photos: Richard Holdener

The simple fact that Holley offered different configurations for their popular LS Hi-Ram intake meant that, at some point, they all had to be tested. In truth, the Hi-Ram configuration chosen will be more of a fitment issue, as the front-mounted, single throttle body will most likely be employed on a normally aspirated or blow-through EFI turbo or supercharger configuration. By comparison, the dual-quad, carbureted combo will most likely be run on a high-rpm, normally aspirated (carbureted) motor. It is possible to blow through the dual carbs or the dual 1000-cfm, 4-hole throttle bodies for that matter, but the throttle size and flow rate will become less of an issue under boost. Toss in the already tall intake configuration and it is easy to see that these different tops are less competition to each other than they are to other after market LS intakes. That said, we decided to illustrate what they each do on the same LS combination. If nothing else, it should stir up the old carbs vs computers debate.

To properly test the different Hi-Ram configurations, we needed a test motor not only capable of making decent power but doing so at the proper rpm range. The tunnel- ram configuration was designed to promote power production higher in the rev range than a factory (long-runner) intake and the test motor needed to be configured to take advantage of that high-rpm power potential. Starting with a 5.7L LS1, the stock block was honed and treated to a set of JE forged (flat-top) pistons and 6.125-inch K1 rods. The stock crank was deemed adequate and the short block received a COMP 289LRR cam that offered .624 lift (intake and exhaust), a 239/255-degree duration split and 114-degree LSA.

The piston/rod LS1 was topped with a set of CNC-ported RHS heads (no longer available), stock rockers and of course the Holley Hi-Ram lower intake. For this testing, Holley also supplied a set of 50-pound injectors, Dominator management system and both of the Hi-Ram tops for testing. Also part of the package was a pair of 1000-cfm throttle bodies and 650 HP carbs. Each combination was tested at the same air, oil and water temp as well as an optimized tune-meaning air/fuel set at 13.0:1 and timing at 30 degrees. Timing sweeps indicated a drop in power at lower timing levels and no power gains above 30 degrees. Check out the graphs to see the difference in power but, if these results are any indication, the winner here is anyone who chooses to run the Hi-Ram.

For this test the Holley Hi-Ram was first equipped with the 102-mm, front throttle-body lid (pt#300-219). Equipped with the front throttle body top and 102-mm FAST throttle body, the Hi-Rammed 5.7L produced peak numbers of 568 hp at 7,200 rpm and 450 lb-ft of torque at 6,100 rpm. We then replaced the front throttle body top with a dual throttle body top (pt#300-216) and a pair of Holley 4150, 4-hole throttle bodies (pt#112-577) flowing 1000 cfm each. Equipped with the dual 4150 throttle bodies, the Hi-Rammed 5.7L produced 574 hp at 7,100 rpm and 456 lb-ft at 5,900 rpm. The front throttle body configuration offered slightly better low-speed power up to 4,700 rpm, but the dual throttle body offered a consistent power gain from 4,700 rpm to 7,200 rpm.

After running the dual 1000-cfm, 4150 throttle bodies, we replaced them with a pair of Holley 650 Street HP carbs (pt#0-82651). For this test, the carbs were used only as throttle bodies and fuel was still provided by the Holley HP management system and 50-pound injectors. Equipped with the single throttle body, the 5.7L produced 568 hp at 7,200 rpm and 450 lb-ft of torque at 6,100 rpm. Using the dual 650 HP carbs as throttle bodies, the injected 5.7L produced 571 hp at 7,100 rpm and 454 b-ft of torque at 6,100 rpm. Running the dual 650 carbs as throttle bodies offered more power than the single, front-mounted throttle body configuration, but it did not match the output of the dual, 1,000-cfm, 4-hole throttle bodies.

The final test was to run the 5.7L with fuel being provided by the dual 650 Street HP Holley carbs. The baseline was still the Hi-Ram equipped with the front-mounted throttle body which produced 568 hp at 7,200 rpm and 450 lb-ft of torque at 6,100 rpm. Using the same timing curve, the carbureted Hi-Ram produced the best power numbers of the day with peaks of 578 hp at 7,100 rpm and 462 lb-ft of torque at 6,000 rpm. Thanks to charge cooling, the carbureted combination offered consistent power gains through the entire rev range. We know from the previous test between the 1000-cfm throttle bodies and using the 650 carbs as throttle bodies that the 4-hole throttle bodies flowed more air, but the introduction of the fuel at the top of the runners more than offset the extra airflow. This also means there might be a few extra horsepower by switching to a pair of 750, 850, or even 950 HP carbs.

Sources

COMP Cams
compcams.com

Holley/Hooker
holley.com

Lucas Oil
lucasoil.com

RHS Cylinder Heads
racingheadservice.com