Speaking of applications, to properly demonstrate the performance merits of the tunnel ram, we needed a cool big-block Chevy test motor. Rather than order a GM crate mill or screw together a rebuilt 454, we took Westech's Steve Brule up on an offer to use the race motor from his record-setting jet boat. The 476 was a serious piece, featuring 13.6:1 compression, CNC-ported heads from AFR and a serious sold roller camshaft. The 476 was basically a .100-over 454 that featured a Scat 4340 forged crank and matching rods combined with a set of JE pistons.
Breathing came from a set of 335cc (intake port volume) AFR aluminum heads. According to the flow bench, the heads flowed 410 cfm at .800 lift (not an unrealistic lift value given the wild cam timing). Comp supplied the hot roller cam (and the remainder of the valvetrain) that featured a .780/.744 lift split and a healthy 282/288 duration split (measured at .050). Additional components used in the build up included a Moroso oiling system (including marine pan and vacuum pump), a complete MSD ignition system (including crank trigger) and a set of 2.25-inch (primary size) Hooker headers.
As mentioned previously, an intake manifold should be chosen for a particular engine combination as well as the intended application. On this particular engine, the effective operating range was rather small, given the fact that the jet boat work much like a high stall converter. Once you hit the throttle to start the quarter-mile pass, the engines speed instantly climbs (up to around 6800 rpm) and the boat accelerates as the flow through the jet pump catches up with the engine speed. This means that the change in engine speed during the run is very minimal (500-800 rpm), and that every attempt should be made to maximize the power production in that rev range.
Having run the motor successfully with a combination of an Edelbrock Super Victor intake (with Dominator car flange) and a Barry Grant 1195 King Demon RS carb, Brule was looking to further improve the power output of his race motor. Given that it made peak power near 7400 rpm and the relatively narrow operating range, Steve decided the engine might be a good candidate for a tunnel ram. As he found out, not only was the tunnel ram impressive at elevated engine speeds, but it shined down low as well.
The first order of business was to establish a baseline with the Super Victor intake and 1195 Barry Grant King Demon carb. Equipped with the single four-barrel, the 476 produced 870 hp and 644 lbs-ft of torque. The power output was impressive considering the relatively small displacement. After successful back up runs produced the same power numbers, we replaced the Super Victor with the Dart tunnel ram and dual 1095 King Demon carbs. The longer runners in the Dart tunnel ram combined with the increased plenum volume and additional breathing offered by the pair of BG carbs to produce some impressive power gains.
Equipped with the Dart tunnel ram and dual King Demons, the 476 pumped out an even 900 horsepower and 670 lbs-ft of torque. Not only did the tunnel ram improve the peak power numbers, but the impressive induction system elevated to power and torque curves from 6000 rpm to 7400 rpm. Basically, the tunnel ram offered more power throughout the tested rev range. At these elevated specific output levels, it is difficult enough to even improve the power output, let alone show consistent gains throughout the rev range. The Dart tunnel ram was definitely the hot set up on this marine motor.
While this particular test was run on a dedicated race motor, we also ran another tunnel ram test on a much milder combination. The test mule was a low-compression 496-inch (.060-over and 4.25 stroker crank) big-block equipped with AFR 315 heads, a mild hydraulic roller cam (255/262 duration) and a set of Hooker Chevelle street headers. It was tested with a single-plane Holley 300-5 intake and a Weiand Hi-Ram (street/strip tunnel ram). The Holley intake was run with a 950 HP carb, while the Hi-Ram was run with a pair of tunnel-ram specific 750 cfm carbs.
Equipped with the single-plane Holley intake, the 496 produced 652 hp at 6300 rpm and 578 lbs-ft at 4800 rpm. After swapping on the Weiand Hi-Ram, the peak power numbers jumped to 687 hp and 618 lbs. ft. of torque. As with the 476 race motor, the tunnel ram improved the power output of the 496 stroker throughout the rev range (from 3000 rpm to 6500 rpm), further illustrating the impressive low-speed and mid-range power offered by the long-runner design.
Of course all the extra power comes with the cost of cutting a hole in your hood, but hood scoops are cool too, especially when they cover a trick (and effective) dual-carb tunnel ram.