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628HP LS7X BUILD

Taking the Already-Efficient High-Line LS-Series Small Block to a New Level of Performance—They Call It the LS7X

Some of the greatest feelings in life come with a rise in rpm, a dropped clutch and tests of traction stretching the boundaries of our physiology. These are the emotions many of us cherish, and while many factors can evoke such emotions, the single most influential force behind these kinetic kicks is torque (which is then equated into horsepower).

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Picture of Stephen K. Anderson

Stephen K. Anderson

Photography Courtesy Bill Mitchell Perfromance (World Castings)

EDITOR’S NOTE: World Products, originally founded by Bill Mitchell Sr. in 1987, is now part of Bill Mitchell Products (BMP). In 2011, Bill Mitchell Jr. acquired World Products’ aluminum product line, including the Warhawk LS7X engine components, and continues to manufacture and sell these products under the BMP brand.

The Thrill of Horsepower and Torque

Some of the greatest feelings in life come with a rise in rpm, a dropped clutch and tests of traction stretching the boundaries of our physiology. These are the emotions many of us cherish, and while many factors can evoke such emotions, the single most influential force behind these kinetic kicks is torque (which is then equated into horsepower).

Components Behind the Numbers

Beyond these numbers are the components united to produce the measurable results we long for, which in the end are the efficiency and dependability of all the individual components we unite that determine our return on investment and, more important, the level of excitement created between the gas pedal and the pavement below.

Room for Improvement Beyond Factory Performance

While automakers have gone to considerable lengths to expand the output and efficiency of today’s engines, continually refining existing designs, as well as searching for that next new level of internal-combustion components, there is often room for improvement in what the factories provide, as the final result must comply with warranty and emissions constraints—an extremely complex equation. They are also governed by cost constraints levied by bean counters and myopic managers with little or no understanding of performance, or the real cost of innovation. Engineering improvements are often not enough, as they too are governed by the cost of development. What really matters—beyond the end use that the engine and its parts were originally designed for—reflects on the capability within the field, and how enthusiasts and high-performance purists put them into application.

Extracting the Power Left on the Table

With power left on the table, it is the goal of the enthusiast to extract that power. Enter all manner of high-performance add-ons and power enhancers that will test the mettle of anything Detroit has to offer. And this is where some assemblies get into trouble, and why the small-block Chevy has been the darling of rodders everywhere. Also aware of that power left on the table, Bill Mitchell Products understands just where that power was left. As it has repeatedly built upon existing corporate foundations, making them better with enhanced casting cores, this has resulted in its own line of engines, basically. Starting with newly designed components intended to wring out unrealized potential, yet fit within the stock confines (sometimes), these Bill Mitchell Products engines are refined to all-new standards. Every one of them purpose-built, the parts and engines go through extensive research and development long before new castings are machined into geometric perfection. Then everything must be tested on the dyno for power and durability. Anything less would be only warmed-over parts. While they may offer improvement, such parts would be prone to breakage, just like the originals, which is why Bill Mitchell has gone to such lengths to improve on how the internal parts work in more demanding displacements and power levels within castings that can handle all the abuse.

Building Upon Proven GM Foundations

GM built the original LS1 over a decade ago, and Bill Mitchell Products built upon the beauty of this simple and highly capable engine design, just as it did with the small block and the infamous Merlin big blocks and heads. Now it has its own line of products that not only replace existing componentry but also improve upon the power capability. From bare blocks to reconfigured cylinder heads, and matching every component in between, it’s easy to see the high-performance benefits of these highly effective components.

The Evolution of the LS7X Design

That now has been translated to high-level LS designs, improving on the 427-inch naturally aspirated LS7. At Bill Mitchell, that translates into a brand-new LS7X design, which we’ve chronicled in Chevy Rumble before. You can have it your way—a complete engine straight off its dyno test and ready for installation, or you can opt for a partial engine assembly so you can incorporate a specific induction system, or whatever else you wish to personalize. Or you can buy all of the parts and build your own. As with all Bill Mitchell engines, and the parts that fill them, when you consider a Bill Mitchell Products high-output crate engine as special as the LS7X, know that they are built to provide a reliable and powerful return on the dollars spent, which was the whole idea of this design improvement in the first place.

Following the LS7X Assembly

Although discussing, reviewing and writing about these engines provides insight into the benefits these components offer, we couldn’t wait to follow the assembly of one. That’s the best way to illustrate the quality of components and how they all fit together, so you are aware of every component, as well as the types of crate engines in the Bill Mitchell Products inventory.

From Prototype to Performance

This particular engine assembly process is a special one, as we followed the early prototyping stages of Bill Mitchell’s LS7X engine from the bare bones up. And while we will review only some of the details incorporated here, you will no doubt understand why Bill Mitchell Products engines have gained the strong following they have today. It’s all about quality and the parts, and the fact that such power is only an e-mail or phone call away. It’s truly astonishing!

Impressive Numbers, Proven Performance

If it’s numbers you’re looking for, how’s this? Here’s an extremely streetable LS7X engine that pumped out 628 hp at 6,200 rpm and 578 lb-ft of torque at only 5,200 rpm. How’s that for impressive? Here’s how it was built.

1. Based on the LS7 engine first used in the C6 Z06, Warhawk LS7X block is an entirely new casting that incorporates numerous improvements designed for reliability and power production.
2. Once the block was prepped (we’ll skip that part here), with the cam and timing gear installed, the block is readied for assembly. Quality ARP studs and fasteners are used throughout, which is something you should consider in any performance application, as the assembly is only as strong as its weakest link, and that would be the bolts.
3. A relief was created for every point of potential interference—between the block and reciprocating components—which is generally the result of larger assemblies from increased displacement. And you thought 427 was big for a small block!
4. Long before the clearanced and polished crankshaft is set into place, the six-bolt-main caps are fitted along with the main bearings. The main bearing clearance would have been addressed previously, and clearanced accordingly, providing the align boring of the main bearing saddles
5. Care is taken to ensure that the main bearings are set and torqued properly before final clearances are double-checked to ensure a perfect interface with the crankshaft. This attention to detail is what builds long use into such an assembly.
6. Parts choice is dependent on a number of variables, and heading that list of priorities is quality and durability. World Products uses a lot of Eagle crankshafts, as they have proven over time to be extremely durable at high power levels. This is the sort of experience you get when you build as many engines as come out of the World Products facility.
7. This special reluctor wheel is part of a no-cost option. Final parts choice, of course, depends on the application. World will ask the questions if it is building the engine, or you need to ask the questions if you are buying the parts to build.
8. Every Eagle crankshaft is micropolished to obtain a low frictional value—between the crank and the main bearings—thereby reducing long-term wear and adding many happy rotations. Engine life expectancy is not an issue with a World Products engine, and the company has warranties available for specific uses.
9. The next step is preparing the crankshaft for balancing. The more horsepower an engine makes—and this one will make a bunch—the more critical an exact engine balance becomes. This is the stuff that goes beyond ordinary machine-shop quality.
10. To achieve the perfect balance of the reciprocating components, pistons, rods, bearings, pins and piston rings are weighed into the equation and balanced to the lightest assembly. A calculation is also added for oil weight—that’s how close all this gets.
11. Weights are added to determine—within extremely close tolerances—where weight should be removed from the crankshaft. This is also done for all the other components: pistons, rods and rings. It’s all done to arrive at the perfect balance.
12. As nearly perfect as possible, the crank is carefully lowered into the newly installed main bearings and adequately lubed before the main caps are fitted.
13. As always, tightening the main caps is a critical process that should involve a precise spiral-tightening sequence as the torque load is increased with each pass, until final torque-load specifications are obtained. Then they all are checked again.
14. All the rotating components, gaskets and fasteners are laid out in a specific order, designated for each hole in each cylinder bank. This makes it easier to account for everything when working with high-end, quality components, and to avoid potentially costly mistakes.
15. Each of the Total Seal top rings is fitted in the bore here to check for end-gap clearance. Each ring is measured and clearanced to fit a specific bore. Prior to this final fitting, the rings are also checked with the piston for proper side-gap and back-gap clearance, to make sure the ring grooves are all proper. When this is done, the rings are assigned the hole and piston in which they were fit.
16. Most rings require some end-gap grinding to create the perfect gap—to maximize compression and reduce leak-down on the top ring. The second ring is a scraper ring and is a little less critical. An oil sealing ring—the next one down—is especially critical for ring pressure. Although every engine may not be checked this way, one way to determine initial ring selection is to pull-test a piston within the bore with an oil ring properly installed, recording the amount of pressure required.
17. As with every process, installing the rings within the pistons’ lands is done with care so as not to damage the ring lands. The relative position of the rings is also critical to sealing, as end gaps are staggered so they are not in line.
18. With the ring retainer snugly fit around the pistons and rings, the piston/ring/rod assembly is tapped into the bore with a rubber hammer, or the end of a wooden handle. No metal here, as this is gentle force.
19. Peering down into the bores leaves no doubt as to the quality of the hardware. This thing is going to run, and that’s not by accident. First the quality is built into the block; then the proper and matching components are selected; and then the assembly is properly fit and carefully assembled. That’s the secret, which is not much of one, really. It’s more a matter of paying attention to details and selecting all the right parts and ensuring they fit as required. Then you can worry about tuning.
20. After being only snugged for the initial rod and cap installation with the engine right side up, the engine is turned over (upside down) in order to fully torque the rod bearings, again in a rod-to-rod pattern, rotating from bolt to bolt and in a sequence of loads that gradually stretches the rod bolt the required amount. To eliminate side loads on the bearing face, insert the proper-width feeler gauge between the rods to eliminate rotational movement.
21. Installed earlier in this initial buildup, the cam chosen for this engine configuration is a special grind that World Products chose for use with this engine. The cam is the popular LS-series Comp Cams hydraulic roller, which seems to be the go-to choice for high-output LS Chevy engines. Comp was one of the first, if not the first, cam companies to fully develop a complete line of LS engine cam and valve gear, and that development has paid off with more power with even a simple cam upgrade.
22. The World Products LS7X incorporates improvements to the front oil-transfer passages to increase oil flow. These are the engineering upgrades that are done so that you do not need to travel that trial-and-error road. The work is done for you.
23. The camshaft retainer plate is a beefed-up design compared with the original part, and that is to ensure absolute placement at high rpm when the valvetrain loads are at their highest, and where you want all the stability and proper cam timing.
24. One of the most important aspects of any engine is determining the precise camshaft timing. That’s the magic, if there is any, and here is a twin-row chain that doesn’t stretch, thereby protecting that timing. It’s also used for added longevity, which is needed in an engine of this ilk.
25. When building an engine, a degree wheel is as common as a 9/16-inch wrench. Here, one is utilized—along with a reference pointer and a dial indicator—to determine the exact location of the pistons so that the camshaft timing can be checked and the cam positioned just so.
26. With the measuring devices in place to determine TDC initially, the crankshaft is carefully worked until it is perfectly positioned.
27. With the piston at TDC, the cam is installed (timed) at the ICL (Intake Centerline) indicated on the cam card. Unless you have experience advancing or retarding the camshaft, the most common place to start before fine-tuning cam placement is where Comp has ground the cam profile. World determines its own cam centers on which its cams are ground. But all this information is provided to the end user.
28. With the camshaft properly timed, the oil pump is fitted. We should note that the oil pump has been clearanced to fit around the special timing chain; this was done not at this point of final assembly, but rather during the engine mock-up stage. Final assembly is a clean procedure—no grinding here.
29. With the gasket in place, the front cam cover is fitted, leaving the front of the engine extremely clean and oil free. Care in assembling these components will ensure you end up with a leak-free engine.
30. A new oil pick-up has also been installed with great care. A failure here would starve the engine of its essential ingredient, oil, and spell disaster.
31. With the short block completed, time was taken to look over all the various details once again just to be sure this engine was ready for the finishing touches.
32. The lifter bores feature an additional stud hole for the six-stud-per-cylinder installation, which can be seen between the lifter bores. World Products’ LS7X heads are equipped with the sixth sealing stud, but if standard heads are used on the LS7X short block, the extra hole is not used.
33. Fel-Pro makes a head-gasket set especially for the new LS7X bolt pattern, with support for the extra head studs, and, as always, the quality of these head gaskets is top notch. The wrong head-gasket selection could create head-sealing problems later on, or even initially.
34. Of all the redesigned components fitted in this engine, the World Products aluminum cylinder heads are the most valuable. Not only do they enable incredible airflow, but they are also very stout units that provide excellent cam-gear rigidity.
35. Manley valves are a favorite at World Products, and here the stainless 2.08-inch intake and 1.60-inch exhaust valves provide excellent ingress and egress of the carefully conceived 64cc combustion chamber.
36. Extensive port modifications have been employed to maximize flow throughout the engine rpm range. And because World understands that these heads would be used with larger small blocks, they were designed to flow accordingly.
37. Once the heads are bolted down—a careful process—you are heading for the home stretch, but here is where lots of attention is paid to the final details of installation of the valvetrain, as well as the components that will ultimately seal up the engine.
38. After double-checking again, the Moroso oil pan and gaskets was carefully put into place, fitted accordingly and bolted down. Care should be taken when bolting down the oil pan, as the bolts are run down in sequence and torqued to the accompanying specs.
39. A beautiful pair of headers was fitted next—this for the dyno—and if looks tell you anything, it’s that this engine will be nothing if not impressive. It’s advisable to discuss header requirements with World, as the final selection, regardless of how good they may look, should be matched to the intended use, and that includes tubing size and length.
40. Long-term reliability is enhanced with the addition of a System 1 oil filter, which pulls more particulates from the oil. This is just another step to ensure that all the quality parts are protected from foreign particles that have the potential to shorten engine life.
41. The rocker arms were fitted next. These beautiful and strong units feature a 1.7:1 lift ratio. Even stock, the LS-series valvetrain is substantial.
42. An Edelbrock Victor Jr. manifold was fitted between the heads, and for good reason: it provides exceptional distribution and flow capability. Bill Mitchell designed his LS7X to be used with either carburetion or electronic fuel injection. He provides a four-barrel setup only, but will ship his engines minus these parts so that you can apply your own special EFI setup.
43. To increase spark intensity, individual MSD coils are fitted to the valve covers. You can also mount them remotely for an even better look, if you are using the LS7X for a custom installation.
44. Initially, a large 4500 AED Fuel Systems carburetor was fitted along with the appropriate plumbing to determine the best combination. From here, just about any combination that works for you can be applied. The beauty is that you can tailor the induction system to your specific needs.
45. To determine the gains realized through World’s latest developments—as this has been an ongoing development—this early “research” engine was carefully mounted in the dyno so that comparisons could be made throughout the engine rpm range. From here, even further developments can be made in any part of that rpm range—again, depending on the application. With all the displacement these engines offer, almost anything is possible.
46. A dynamometer is many things, including a method of breaking in an engine, testing durability and determining actual torque and horsepower of a particular combination. It’s interesting to note that every World Products engine comes complete with a dyno readout. That’s important so that you know not only what power your engine develops, but also where it develops that power. This will allow you to tweak your power needs where that power best suits your application.
47. Offering greatly improved spark value over the stock coils, these MSD coils provide complete combustion, thereby raising output. They work so well that they’ve become a must-have item.
48. Fully hooked up front—fuel system to exhaust—this World Products LS7X 427-inch small block is ready to run some tests, and what tests they turned out to be!
49. While a smaller 870-cfm four-barrel was run initially on the first dyno test, it proved to be a limiting factor in the power equation—too small. So a 1,050-cfm deep-breather replaced it, with notable results.
50. From the safety of the control room, the LS7X was fired and run through its paces with the new, larger carburetor, returning 628 hp at 6,200 rpm and 578 lb-ft of torque at 5,200 rpm. Of particular interest was that this engine retained over 500 lb-ft above 3,500 rpm! Impressive? We’d say so. Consider, if you will, that this is not a big block, but a big-inch small block. If that doesn’t get those power juices flowing, it’s time to get your pulse checked. What’s more, now you know just how it was done, and how straightforward netting over 600 hp from a small-block LS can be.

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Bill Mitchell Products

1726 Hibiscus Dr.
Edgewater, FL

(386) 957-3009

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