409ci LQ4 Iron Block LS - Proven Powerhouse

Starting with an iron block LQ4 plucked from nothing more exotic than a Chevy Suburban, the engine featured here was built to compete in our annual AMSOIL Engine Masters Challenge engine-building competition. The goals of the event are similar to that of a serious street application: delivering the broadest powerband over an rpm range from 2,500-6,500 rpm, while running on pump gas. While the factory LQ4 comes through with a generous displacement of 366 ci via the stock 4.00x3.62-inch bore and stroke, one of the appeals of these engines is how readily they take to added displacement via a stroker crank. The most common stroker combination for this series of engines is to substitute a 4.00-inch crank, yielding a displacement of over 400 ci with a clean-up overbore. This particular engine spec’d at 409 ci after the bores were machined .030-inch oversize.

As with the crank, the rest of the rotating assembly consists of readily available, off-the-shelf parts. The rods are also from Scat—their 6.125-inch I-beam units. “We use a lot of this style of rod on our circle track engines, and we are really comfortable with them,” Andy says. “They are a little lighter in weight than an H-beam, and are more than adequate for this application.” Finishing the internal components of the stroker assembly are a set of Mahle forged pistons, wrapped with a Total Seal gapless top ring set in a 1.5/1.5/3mm package. Andy tells us that the factory block readily accepts the long-stroke crank, and it literally dropped right into the main saddles with no custom clearancing or grinding required. It simply doesn’t get any easier than that. The crank spins on King bearings, and was installed with .003-inch clearance at the mains, and .0024 on the rods.

While the LQ4—like all LS-based engines—uses a complicated engine management system and EFI in OEM installations, for general-purpose hot rod use there are simpler alternatives. To handle the induction, the EFI was shelved in favor of a GMPP two-plane intake manifold topped with a D&A-modified Holley 750HP carb. The attraction here is that the fuel system requires no wiring or programming to make it work; just plumb it up and it’s done. Andy was impressed with the manifold: “It’s a really nice piece. There is plenty of room to port on it if need be. I didn’t do any port work on it, and it made for a really nice broad torque curve.”

Power Testing

With the final dyno printouts in hand and the engine cooling on its stand, the numbers told the story. The short-cammed, big-cube stoker delivered tire-melting torque from the word “go,” showing 530-plus lb-ft right from the jump at 2,500 rpm. From there the torque just ramped upward, peaking at 581 lb-ft at just 3,200 rpm. While the low-rpm torque peak might imply that the engine would quit early, the torque just seemed to plateau, holding over 500 lb-ft all the way up to 6,000 rpm! Peak power was recorded at 588 hp at 5,800 rpm. If you are looking for wild torque, and power that keeps coming, A D&A Machine Shop stroker LQ4 will dish out the numbers.

On the Dyno 409ci LQ4 Chevy