Text by Sam Logan.
Photography by Moore Good Ink.
In the dyno room, Lamar Walden’s first production road-going 409 fitted with twin 625 Street Demon carburetors revved with enthusiasm to 6,293rpm and generated 602.4 peak horsepower and 602lbs-ft torque at 4,600rpm. For some, the emergence of the new Street Demon and the re-emergence of a new 409 have been the biggest hot rodding news of 2012.
Earlier in a comparison test, twin Edelbrock AVS carburetors had generated a commendable 553hp @ 5,800rpm and 575lbs-ft torque @ 4,470rpm. Why had the Street Demons triumphed by 49hp and 27lbs-ft of torque? “I imagine,” said Lamar, “its supremacy lies in the size of its secondary throttles.” Unlike any conventional 4-barrel layout, the Street Demon is a three-barrel carburetor inhibited by few restrictions—the secondary throttle bore is one big opening.
It’s taken Demon a while to compose a convincing answer to the Edelbrock AVS. But once Larry Tipton, Demon’s distinguished senior designer, focused his creative energy on the new design in 2010, we suspected a beacon of carburettor ingenuity could be in the works. And when it appeared on May 25, 2012, it not only looked the part in a market where appearance is of primary concern but also it proved to be a very strong performer.
Based entirely on a brand-new concept this innovative three-barrel 625 Street Demon has noticeably smooth contours especially around the air entries, unlike its Edelbrock counterpart. Though both carburetors have dual mounting points, accommodating square-bore or spread-bore manifold mounting without adapters, Tipton is particularly pleased with the effectiveness of his triple-stack boost venturii arrangement. Set in compact 1-3/8in primary throttle bores, selected to induce fast-moving airflow, “This layout,” he says, “delivers superior air-fuel emulsification and as a result the acceleration will be crisp. The fuel economy for street performance will also be heartening.” But for this first test of Lamar Walden’s new LWA 409 high-performance hot engine, two Street Demons set in tandem were stipulated. To date twin Street Demons have never been run before.
Originally appearing in the Chevrolet Impalas of the early1960s, the outward contours of these new cast aluminium 409 engines remain unchanged; their cylinder heads and valve covers exhibit the same alluring W shape. However, the internal power-making capacity is entirely modern. Since this was the first occasion that twin Street Demons would be used in tandem, we were enthralled by the challenge. “Come on down to Doraville,” was Walden’s cry, “and let’s make some noise!” Lamar, a warm, congenial man with fifty years of race-engine building experience, is currently receiving his first batch of 50 LWA 409 aluminum engine blocks—all of which, he reports, are sold.
This particular 409, which is endowed with a 4.375in bore and 4.000in stroke, thus a displacement of 481cu in, is destined to power an Impala on the streets. It will run 93-octane pump fuel with 10:1 compression ratio. Though the engine’s 4in stroke permits ample time for cylinder-filling, a hydraulic roller camshaft was selected with a lobe separation angle of 111 degrees (lobe centerline angle) because this Impala requires at least 10in of vacuum to run its power-assisted brakes and other accessories. Hence its longish stroke length and modest valve-open overlap maintains a comfortable reservoir of vacuum.
Finally the engine is completed with LWA cylinder heads containing intake and exhaust valves of 2.250in and 1.740in respectively, valve lift of 0.650in and 0.680in, and an Edelbrock intake manifold. The Edelbrock is similar in design to the original. Though taller in dimension, LWA makes an alternative intake available that yields significantly higher performance for those with greater bonnet clearances.
Set in tandem atop the first production LWA409 we were interested in not only the tuning procedures needed to get the two Street Demon carburetors to produce their peak power but also we wanted to know how they’d compare against the established Edelbrock AVS models.
So here we are: this is a tale of a test of the first twin 625 Street Demon carburetors on the first new 409 hot rod engine. Clearly, these carburetors fared pretty well and there is reason to think the future is bright for this gutsy decision—a decision to create a brand new carburetor in 2010 that became a reality in 2012! Who’d have thought it? Here in this sequence of photographs and captions is how the engine tests unfolded.
Lamar Walden Automotive