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Dec 23, 2023

World’s Biggest Chevy LS Engines Being Built With 527 Cubic Inches!

There seems to be no upper limit to the capability of GM's versatile LS V-8

There seems to be no upper limit to the capability of GM's versatile LS V-8 small-block engine family, both in terms of horsepower output and displacement. Throughout the 1960s, the distinction between small-block and big-block engines came into vogue, with the muscle car revolution bringing into the limelight big-block engines with ever-increasing displacements. Within a few years, numbers like 383, 390, 392, and 396 morphed into numbers like 429, 440, 454, and 460—and those were the big-blocks. Today, we report that the small-block LS is now being built to the majestic size of 527 cubic inches, thanks to Horsepower Research of McKinney, Texas.

HPR earns this distinction by virtue of a Dallas-area customer named Ed Loutherback, who has commissioned the company to build not one but two 527ci LS engines for separate projects. The first one is for a racecar—a 1995 Pontiac Trans Am destined for HOT ROD Drag Week—and the other will be for a street car—a 1965 Chevy Biscayne. HPR's choice as the builder of the two largest LS small-blocks ever assembled came after another of HPR's customers, Chris Ramey, won the 2020 Optima Ultimate Street Car Invitational in a highly modified 1986 Corvette with a naturally aspirated 468ci LS built by HPR. These two new engines headed to Loutherback will be larger and more powerful yet.

One thing that stands out with both of these humongous LS bullets from HPR is that neither of them will rely on a power-adder. That's right—no nitrous, no turbos, no blowers, no monkey business. They will have to earn their billing the old-fashioned way, with muscle alone. Though that certainly appears to be the straightest path between two points, it's not an easy road to follow because, unlike with power-adders, you can't gloss over any of the potential choke points for power production. When pure cubic inches and rpm are all you have to make the number, the parts that go in need to be the best, and with HPR's twin 527ci LS engines, they are indeed.

HPR started both builds with the RHS 9.750-inch tall-deck aluminum LS block, which adds an extra 0.510 inch of deck height to the standard 6.0-liter deck height of 9.240 inches. This provides the extra displacement (check out some cool block-clearancing operations in the photo gallery) from a 4.185-inch bore and a 4.800-inch stroke, yielding 527 cubic inches of displacement, provided by a pair of identically-prepped Sonny Bryant billet-steel crankshafts.

Besides the long arm of the Sonny Bryant billet-steel crankshafts in both engines, the HPR 527ci LS small-blocks will rely on H-beam Callies forged rods, but due to current supply constraints, HPR says future versions would likely be built with Dyers rods. The forged pistons in both engines are a custom design, and here things vary considerably due to the street version needing a lower 11.75:1 compression ratio for pump gas. For the 527 slated for the street-driven Biscayne, a custom Wiseco 2618 forging was ordered; the 15:1 race engine for the '95 Trans Am gets race-gas-ready forged 2618 slugs from CP.

On top of both 527ci LS engines sits a pair of similarly prepped CNC-ported cylinder heads from CID. Both feature oval-port intake runners with 323cc volume, Victory titanium valves (2.25-/1.60-inch diameter), and T&D shaft-mount 1.9:1-ratio billet-steel rocker arms. Since both engines will make their power naturally aspirated, it's imperative that airflow be as unrestrictive as physically possible, and both HPR bullets will provide for that in spades, with one important difference: the street version with 11.75:1 compression will be dialed back from the edge in order to run on premium pump gas, whereas the 15:1-compression race version will be knives-out!

The race-ready 527 LS goes a step further with a 60mm cam journal, which provides for higher-lift lobe profiles—in this case a solid-roller camshaft that tops out at 275-/295-degrees of duration (at 0.050-inch lift) and an incredible 1.008 inches of lift on the intake side and 1.001 inches of lift on the exhaust side. (Note that the RHS block can be machined for the larger-diameter, race-style cam journals.) A set of Jesel 0.937-inch-diameter roller lifters with keyway guides in conjunction with half-inch-thick Manton pushrods was used, and as a point of interest, HPR says traditional link-bar-style lifters experience binding when used in conjunction with valve lift this high, thus the need for keyed lifters. By contrast, the street-version 527ci LS uses a hydraulic-roller setup with stock-style link-bar roller lifters acting on 7/16-inch-diameter Trend pushrods. On the street engine, an LS-standard 55mm diameter journal camshaft is used, with 250-/260-degrees duration and 0.750 inches of lift.

Where the two engines differ significantly is in the induction department. Though both of the 527ci LS engines are slated to use electronic fuel injection, the paths that the air and fuel take will be largely a function of aesthetics and end-use. For the 1965 Chevy Biscayne's street engine, an individual-runner Hilborn injection unit from Holley will be deployed, the benefits of which include crisp throttle response and a strong, street-friendly torque curve—not to mention a sexy retro styling that will drop jaws on the show circuit. The drag unit planned for the '95 Trans Am headed to HOT ROD Drag Week will get a CID-sourced split-single-plane intake fed by an Accufab 4500-series throttle body sporting 2.5-inch butterflies. Injector selection is still to be determined.

To be clear, at the power levels we're talking about, virtually everything in an HPR crate engine is going to be a bespoke piece of equipment. After all, there is only so much demand for an over-the-top engine like a 527ci LS, and every customer is going to want something slightly different. For comparison's sake, the street-going version with 11.75:1 compression that runs on premium pump gas will make somewhere in the ballpark of 825 hp, and when equipped like this one, with a four-stage dry-sump scavenging system, costs somewhere between $34K and $38K. Moving up to the high-compression 15:1 race version, HPR predicts it will push the dyno needle to around 1,150 hp, and one can expect to pay upwards of $55-58K. Those interested in just the 527ci short-block by itself should be able to pick one up starting at around $22K. Got more questions? You can call HPR directly at 972-597-4367. (Be sure to check out the extra photos in the attached gallery!).

Photos By Horsepower Research