With the Hi-Ram bolted in place, Westech’s Steve Brulé fired the engine to life. After a few pulls to put some heat in the coolant and engine oil, Brulé yanked back on the throttle lever and let the engine sing against the dyno brake. The result was a very respectable 536 horsepower at 6,900rpm and 457 lb-ft of torque at 5,000rpm. The combo worked great with 380 lb-ft on tap as early 3,000rpm and an ample power curve that was almost flat from 6,400rpm to 7,000rpm. This was a powerplant that would be at home in any hot rod or racecar.
The Hi-Ram delivers a blended performance of strong mid-range torque and potent top-end power.
Dyno operator and Engine Masters star, Steve Brulé, stands nearly on tip toes to reach the TPS connector on the Sky-Ram.
With the baseline established, it was time to see how adding gobs of runner length would transform the power and torque curves. There was speculation galore, and a giddiness percolating the dyno cell. Even Brulé, who’s tested about every intake manifold combo under the sun, hadn’t yet tested anything this... weird.
The Sky-Ram was bolted in place on the engine, needing only a lengthened harness connection to throttle position sensor (TPS) since an idle air control (IAC) wasn't necessary on the dyno. With the base of the intake modeled after a Hi-Ram, it installed in the same manner, requiring no specialty hardware. The front-feed plenum up top is a Holley stocking part (300-246) and the same design used on the Hi-Ram. It was a true, apples to apples test.
It was all smiles when the Sky-Ram equipped LS barked to life. It ran, and that checked one box off the list. Brulé put the engine through a series of partial dyno pulls, dialing in the fuel mixture in the Holley HP ECU. The Sky-Ram was truly a different animal and warranted significant changes in the fuel tuneup from the previous Hi-Ram test.
Once satisfied the engine had the fuel it demanded, Brulé queued up the dyno one more time. The moment of truth had arrived.
The Sky-Ram-equipped LS hunkered down against the dyno as Brulé put it through its paces. An audibly different tone bellowed from the cell as the engine churned out 510.8 lb-ft of torque at a mere 3,700rpm, a 53.8 lb-ft improvement in peak torque over the Hi-Ram and 108 lb-ft improvement at the same, 3,700rpm. Power climbed rapidly, boasting a significant 70 horsepower over the Hi-Ram at 3,600rpm. Soon, however the Sky-Ram's early horsepower lead trailed off and it began to show its hand, the inevitable downside to the ultra-long-runner design.
Peak horsepower, 464.5, occurred at 5,100rpm and soon after it ran head-first into a wall. The airflow capability of the runners pegged and power fell off rapidly. Brulé ended the pull at 5,500rpm. While the Sky-Ram rewarded with massive torque gains and a robust power curve, it was down a whopping 71.9 peak horsepower from the tried and true Hi-Ram combination.
When mounted on the engine dyno, the Sky-Ram's massive runners just barely cleared the ceiling of the dyno cell. Because the Sky-Ram isn't a production piece, it lacked provisions for a MAP sensor. One was drilled and mounted onto the underside of the plenum lid. Also, due to the Sky-Ram's physical size, it was 3D printed in two pieces. The pieces were then bonded together and a pair of 1in all-thread bars were passed through its center to add rigidity to the creation.
Runner Length Explained
At this point you may be asking. “Why does runner length affect the powerband?” To answer this question and deliver some context to our test results, we must first define runner length. In internal combustion engines, runner length is considered the distance from the intake port to the source of air entering all cylinders of the engine. On this LS, each cylinder shares a common plenum in the intake manifold, so we will define the runner as the distance from the intake port to the plenum.
As an engine operates, pistons move downward in their bores as the intake valves open. This draws in a mixture of air and fuel and creates a moment of low pressure in the runner. As the piston begins the compression stroke, the intake valve closes, and the volume of high-speed air in the runner that the cylinder didn’t ingest that cycle slams into the back of the closed valve face, creating a high pressure wave. This high-pressure wave of air reflects backward up the runner and subsequently back down the port. These pressure waves endlessly bounce up and down the runner until a point occurs at a specific engine speed where that high pressure air wave synchronizes with the opening of the intake valve. This serendipitous occurrence provides a boost of cylinder filling that helps the engine operate with increased volumetric efficiency, the ratio of the physical displacement of the engine to the amount of air/charge it is actually ingesting. For example, a 350ci engine operating at 100% volumetric efficiency (VE) would ingest 350ci of air per cycle. On well-tuned high-performance engines, it is possible to see VE numbers above 100%.
The Sky-Ram belted out 510.8 lb-ft of peak torque at a mere 3,700rpm, a 53.8 lb-ft improvement in peak torque over the Hi-Ram and 108 lb-ft improvement at the same, 3,700rpm.
By manipulating the runner length (as well as countless other variables) engineers are able to alter the point in the powerband where that wave aligns with the intake valve opening and hence where the engine will perform most efficiently. Longer runners tend to fix this point at lower engine speeds, while shorter runners push it toward higher engine speeds.
The Takeaway
So there you have it, folks. Long intake runners certainly deliver on their promise of increased low-end torque. In fact, the Sky-Ram intake would be a lot of fun in a hot rod. That tire-shredding torque would make for both smiles and smoky burnouts, assuming you don’t mind peeling back the sheet metal of your hood to fit it. However, this exercise in theory and lighthearted fun is not intended for production. For the rest of LS enthusiasts out there–the horsepower obsessed, and time-slip oriented kind–the Hi-Ram remains the better path to power.
