There are many approaches to building engines, but a theme that resonates with practically anyone is maximizing value in terms of power per dollar. Donny and Andy Key of D&A Machine Shop, in Canton, Georgia, quickly concluded that achieving that goal requires a well-thought-out approach. Here the GM LQ4 makes an outstanding starting point. Simply by design, these engines feature loads of inherent power potential. They come through from the factory with ample displacement, and the parts support from the aftermarket means these engines are ripe for modification. The LQ4 version of GM’s LS series of engines has the added advantage of a deep production run in a variety of late-model truck applications. The upshot here is that engine cores are readily available in plentiful numbers, generally at affordable prices.
A 4.00-inch stroker crank...
A 4.00-inch stroker crank will drop right into the crankcase of a 6.0L truck block like this LQ4 with no clearance work required. The rotating assembly here consists of a Scat crank, Scat I-beam rods, and Mahle forged pistons. Mahle bearings ensure everything spins as it should, while ARP fasteners lock it all in place.
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.
The Mahle pistons are flat-tops,...
The Mahle pistons are flat-tops, giving a final compression ratio of 11.4:1, while Total Seal gapless top rings provide the compression seal. The Scat I-beam rods measure 6.125 inches center to center.
Stroker parts for the LQ4 are offered by practically every aftermarket company in the game, meaning the competition is fierce, and prices are reasonable. D&A selected a Scat 4.000-inch crank as the backbone of the combination. As Andy says: “Basically, all we had to do with the crank is balance it. Of course we measured it, and it was right on the numbers. We have never had to return anything to Scat. They are dead on the money, right where they need to be, and they hold up well.”
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.
Simply by design, these engines feature loads of inherent power potential. "