Words And Photos: Richard Holdener

Single or dual plane, the induction argument is as old as the V8 engine itself. While the LS was originally equipped with factory fuel injection, MSD made conversion to carburetion so simple, that swappers were soon faced with the very same question that plagued the previous small-block Chevy owners. Choosing the proper intake is critical for maximum performance, and by maximum we mean not peak power but maximized power through not only the entire rev range, but we should even throw in things like drivability, fuel mileage and even torque converter compatibility.

You see, despite similar peak power numbers, the two Edelbrock (carbureted) LS intakes tested here offered decidedly different power curves and street manners. While we all like to brag about the peak power numbers, the reality is that the vast majority of carbureted LS engines spend MOST of their time well below the power peak. In fact, the vast majority is spent well below the torque peak and even during hard acceleration, the motor spends most of its time accelerating between peak torque and peak power.

How does the choice of intake manifolds alter the all-important average power production? For those new to LS performance (though this carries to every type of V8 regardless of generation or manufacturer), the intake debate between single and dual-plane manifolds comes down to a simple matter of operating (engine) speed. The dual-plane design, like the Edelbrock Performer RPM tested on our LS combinations, was designed to enhance power production lower in the rev range than the single plane. This simple fact makes the dual-plane ideal for the vast majority of street applications. On most performance engines (though not our modified 4.8L), the dual plane will likely sacrifice power at top of the rev range compared to the single-plane design. For a race-only motor, that spends its time at the top of the rev range, racers almost always choose the single-plane, but for the other 97% of combinations including stock, performance street, and street/strip, the dual-plane manifold is a better choice. What the choice often comes down to is what you are willing to sacrifice and where that sacrifice occurs.

We could ramble on endlessly, but dyno results are perhaps the best way to illustrate the power differences. The dyno graphs are limited in that they do not show things like drivability and mileage, but low-speed torque production provides a strong indicator about both. To clearly illustrate the power differences between single and dual-plane intakes, we purposely chose two decidedly different test motors. Running the test on two difference displacement and effective power outputs provided not just dyno numbers but also trends on how the same test might fair on other (different) combos. As indicated previously, similar dyno result can be had with almost any V8 engine combination, but the LS engine family is popular among street rodders and swappers. We also loved the fact that this power plant came from such humble beginnings, starting out life as a simple truck motor.

The first test was run on a modified 6.0L LS (technically an LQ4). The iron 6.0L truck block was machined in preparation for a combo that included the stock crank, Carrillo rods and CP, flat-top pistons (with Total-Seal rings). To help ensure plenty of power, we slid in a healthy cam profile from COMP Cams. The LSr (cathedral-port) cam (pt# 54-459-11) spec’d out with a .617/.624 lift split, a 231/239-degree duration split and 113-degree lsa. The COMP cam was teamed with a set of matching hydraulic roller lifters (pt#850-16) and 7.35-inch (hardened) pushrods. Providing plenty of airflow to the 6.0L short block was a set of Stage 2, CNC-ported 243 (LS2) heads from Total Engine Airflow. Fuel and spark for our intake test was provided by a Holley 950 Ultra HP carburetor and MSD ignition controller (designed specifically to convert the fuel-injected LS to carburetion). The MSD ignition was a simple plug-n-play affair, using the factory coil packs, MAP, crank and cam sensors.

To illustrate the benefits offered by each intake design, we tested them both on the engine dyno under the same conditions, meaning same air/fuel ratio, timing and temperatures. The test motors also featured components from Meziere, Lucas Oil and a set of long-tube headers feeding a pair of dyno mufflers.

First up on the modified 6.0L was the dual-plane, Performer RPM. The quintessential dual-plane, the Performer intake offered both plenty of power and an exceptional torque curve (though we would love to see an RPM Air Gap design for the LS). The 6.0L responded very well to the dual-plane Performer, checking in with peak power numbers of 545 hp at 6,600 rpm and 482 lb-ft at 5,200 rpm. The Performer offered a broad torque curve, with torque production exceeding 450 lb-ft from 3,500 rpm to 6,250 rpm. This test on the dual plane demonstrated that the Performer offered not only good low and mid-range torque, but plenty of rpm capability as well.

Next up on the 6.0L test motor was the single-plane, Victor Jr. intake. Unlike the divided dual plane, the single-plane was designed with a common plenum feeding all eight cylinders. Given the common plenum and attending runner length, we expected the Victor Jr. to excel at the top of the rev range. Not surprisingly, the Victor Jr. bested the dual-plane Performer in peak power (554 hp to 545 hp), but it might surprise a few that the single plane also offered the highest peak torque reading (488 lb-ft to 482 lb-ft).

Looking solely at the peak numbers, the Victor Jr. seems the obvious winner but the power curves tell another story. True enough, the single plane offered more peak horsepower and torque, but the Performer out-powered the Victor Jr. from 3,000 rpm (and below) to 4,800 rpm. Measured down at 3,500 rpm, the dual-plane, Performer offered an extra 28 lb-ft of torque! On this modified 6.0L, the (trade off) question becomes does the extra 28 lb-ft of torque below 4,800 rpm offset the loss of 7-8 hp above that point? Let the debate rage on!

Not content to show the results on just 1 motor, we performed the same intake test on a smaller 4.8L (LR4). Rather than skew the results by using a bone stock 4.8L, we chose to modify the LR4. Modifications to the 4.8L included forged JE pistons (with 7cc domes), a hot cam and a set of ported heads. The new JE slugs (with Total Seal rings) increased the both internal strength and static compression. To further improve power, the wimpy, stock LR4 cam was replaced by a Stage 1 blower grind from Lil John’s Motorsports. The Stage 1 blower cam offered a .610/.586 lift split, a 223/238-degree duration split and blower-friendly 120-degree lsa. We chose this cam because this combination would later see a healthy dose of boost from a Vortech supercharger. The short block was topped off with a set of CNC-ported, Gen X 205 heads from TFS. Additional mods to the little LS included an ATI Super Damper, dual valve springs and hardened pushrods. As with the 6.0L, the MSD ignition controller was on hand to provide proper spark.

Like the 6.0L, we started our test on the 4.8L with the dual-plane, Performer RPM. The small-displacement 4.8L responded very well to the dual-plane design, as the RPM allowed the little 4.8L to rev cleanly to 7,000 rpm. Run with a 750 HP Holley carb, the modified 4.8L produced 440 hp at 7,000 rpm and 352 lb-ft of torque at 5,800 rpm. Those were pretty lofty engine speeds for a dual-plane design. Common sense told us that the high-rpm nature of the combination was better suited to the single plane, but boy were we wrong.

Run with the Victor Jr., the 4.8L produced just 427 hp at 6,900 rpm and 351 lb-ft of torque at 5,500 rpm. Not only did the RPM make more peak power, but it once again excelled at torque production below 5,000 rpm. The dual-plane Performer RPM offered torque gains as high as 40-45 lb-ft of torque. That torque deficit was all the more impressive considering the limited torque production offered by the smaller displacement. These tests may not end the debate, but will provide you the Plane Truth by clearly demonstrating the strength of each intake. As always, the choice is yours.

Tested on the modified 6.0L, the intake swap showed the quintessential single/dual plane conundrum. Looking specifically at the peak numbers, the single-plane Victor Jr. seemed to easily best the dual plane by offering 554 hp and 488 lb-ft (to just 545 hp and 482 lb-ft for the dual plane). Peak numbers, however, do not tell the whole story, as the dual-plane offered as much as 28 additional lb-ft of torque down low while losing out just 7-8 hp at the top of the rev range. The question now is will you miss the extra grunt offered below 4,700 rpm more than the missing 7-8 hp above that point? The choice obviously comes down to the intended application, but both Edelbrock manifolds offered plenty of power on this modified 6.0L.

Much like the test run on the larger (more powerful 6.0L), the dual-plane, Performer intake offered considerably more low and mid-range torque production on the 4.8L. Unlike the larger 6.0L, the dual-plane Performer also made more peak power on the smaller 4.8L. Run with the Performer, the modified 4.8L produced 440 hp at 7,000 rpm and 352 lb-ft of torque at 5,800 rpm. The single-plane, Victor Jr. could only manage 427 hp at 6,900 rpm and 351 lb-ft of torque at 5,500 rpm. On this smaller (milder) application, the Performer was better through the entire rev range, with the exception of a 600-rpm spread from 5,000-5,600 rpm.

Sources

Aeromotive
aeromotiveinc.com

COMP Cams
compcams.com

CP Pistons/Carrillo Rods
cp-carillo.com

Edelbrock
edelbrock.com

Holley/Hooker
holley.com

Lucas Oil
lucasoil.com

MSD
msdignition.com

Total Engine Airflow
totalengineairflow.com

Total Seal Rings
totalseal.com

Trick Flow Specialties
trickflow.com