New FAST LSXR Intake Manifold & RHS LS Race Block - Expanding Horizons

Comp Performance Group Raises The High-Performance Bar With A New Fast LSXR Intake Manifold And RHS LS Race Block

Chris Werner Apr 1, 2009 0 Comment(s)

The folks at COMP Performance Group have been hard at work on a selection of products sure to be an instant grand slam with the LS community, and two particularly interesting items on hand at the shows were a new FAST intake manifold and (introduced at PRI) a new RHS engine block.

Missed both Vegas and Orlando in `08? Brian Reese, Director of Engineering and Business Development at COMP Performance Group, hooked us up with some cutting-edge information on these new products, so read on to find out what everyone's been talking about.

Fast LSXR 102mm Intake ManifoldGMHTP readers are surely well versed on the original FAST LSX intake manifold. Available in both 78mm and 90mm configurations, it took the LS world by storm years back, providing thousands of enthusiasts with bolt-on performance increases for engines mild to wild. In test after test, we've shown these intakes to be proven performers, and the more recent 92mm manifold only upped the ante. But since these manifolds were designed for use with the original cathedral-port heads first seen on the LS1, the company has until now left owners of rectangular-port LS engines out in the cold.

Well, times they are a changin', because FAST has just unveiled its LSXR 102mm Intake Manifold, a piece that delivers increased flow capabilities for rectangular-port (LS3/L92-style) engines. So what makes the LSXR special? Some highlights on this new manifold and details of its development will clue you in.

Design Process
An appreciation of the glory that is the LSXR is impossible without at least a cursory understanding of the engineering that went into it. The science of air flow as applied to internal combustion engines is quite complex, but pretty much everyone already knows that more air enables more power; getting an engine to ingest additional air is the key to increased output. As applied to the intake manifold, the main factors that dictate engine air flow are fourfold: (1) "command," comprising throttle and valve opening events; (2) pressure differential, which can be referred to as "potential;" (3) "obstacles," consisting of flow path and restrictions; and (4) wave tuning, which is a part of potential/momentum. Design of a well-performing intake manifold comes down to proper application of this science and all of its intricacies.

That said, in order to develop the LSXR, Reese and other FAST engineers coupled computer-aided design techniques with dyno testing, and the process began with a thorough evaluation of factory manifolds to determine a baseline to build from. This included dynoing, precise physical measurements, flow testing, and building of computer models that would accurately represent the stock manifolds in digital form. With mountains of data on the factory items now in hand, Computational Fluid Dynamics (CFD) was utilized in order to model air flow through virtual manifolds, thereby creating a "virtual flow bench" for use in the LSXR's development. Among the aspects of air flow looked at and data generated in this process were velocity and pressure diagrams, flow initiation and paths, and evaluations of energy loss. The models proved crucial in the design of the intricate shape of the interior of the manifold, particularly the precise contours of the runners. Important flow considerations included requirements of turning the air (air is lazy and doesn't like to change direction), flow separation concerns, distribution in the plenum, and upstream/downstream considerations. Just as important were tuning considerations, which included: wave tuning (i.e., constructive use of the reflective pressure waves resulting from opening/closing events of the intake valves to give added pressure differential over natural aspiration, forcing additional air into the cylinders); inlet shape and orientation; runner length, taper, area, and shape; plenum volume; and engine variations. Packaging limitations played a role in both.

The engineers also devised a custom "test" manifold, which looked nothing like an ordinary manifold. Rather, it was created purely in the interest of evaluating different intake runner parameters on a dynamometer. In the test manifold used, plenum volume was taken out of the equation, and both runner length and runner area were varied in order to record the effects of each. For example, testing demonstrated a clear 175-rpm torque peak shift for each 25mm change in intake runner length. With a stock baseline runner length of 275 mm, engineers went to both extremes of the spectrum (and everywhere in between): long 465/415mm runners yielded a 27.7 lb-ft and 7 hp gain, while short 210mm runners came up with a 10.1 hp gain coupled with a 20.6 ft-lb loss in torque. A compromise was clearly in order.

When parameters were finally decided upon, it came time to test a prototype LSXR intake, the first time the manifold had existed outside of the virtual world of a computer model. The testing process was a cycle: the runners were first flow tested at a given shape, then were modified, ground, and smoothed as seen fit. Flow testing and more hand finesse followed, then it was time to bolt the manifold to the test engine for results. After dyno data was recorded, the process repeated itself. In fact, while using that all-important dyno, FAST engineers measured not only horsepower and torque, but also AFR, EGT, MAP, and air flow. Consistent dynoing (ex., keeping stable fluid temps) and correct representation of application-specific parts (such as use of a stock exhaust) are aspects the FAST crew took seriously!

Of final note, plenum size was maximized within the packaging constraints dictated by the physical space above the valley cover. In fact, the valley cover of the engine is actually used as a stressed-loaded member of the intake manifold by using rubber bumpers on its lower surface that press against the cover. Engineers opted to have the LSXR include new valley cover bolts to clear the way for the manifold's increased volume, deciding that every bit of extra space that could be afforded was worth it.

Versatility
One of the most impressive facets of the FAST LSXR is the wide range of applications it is designed for, with little or no other underhood changes required. The company touts "perfect bolt-on fitment that allows use of factory accessories without modification or clearance concerns." The manifold accepts stock electronic throttle bodies along with aftermarket 90, 92, and 102mm units. It also fits C6 Corvettes without having to alter the firewall! For the nitrous crowd, there are built-in nozzle bungs that are complemented by the polymer material's high burst strength.

For those so inclined to alter the LSXR's airflow characteristics to fit a highly-modified or otherwise custom application, the manifold's three-piece modular design allows easy disassembly and porting. While prior FAST manifolds were also of a three-piece construction, this latest design features the ability to remove individual runners from the manifold for modification.

Conclusion
Hopefully we've been able to give you a small taste of what the FAST LSXR is all about. Get yours under p/n 146102; final MSRP will be about $997, with replacement runner sets for do-it-yourself porting available for $480.

RHS LS Race Block
With several factory and high-performance aftermarket LS engine blocks already on the market, RHS has decided to add its own entry to the foray with its new LS Race Block. This aluminum piece has arguably the most complete set of features yet seen in an aftermarket Gen III/IV block. Let's get the lowdown on some of them.

Strength Enhancement
With the GM LS7 and all other aftermarket blocks (including competing options such as resleeved factory blocks) set as the benchmarks for improvement, RHS engineers successfully designed a block strong enough to support 2,500 hp (given a skilled builder who incorporates plenty of other high-quality components in the engine, of course). That's a whole heck of a lot for an aluminum block, and it all starts with the company's selection of an A357-T6 aluminum alloy that gets subjected to a unique solidification and cooling process, including chilling of the main bearing bulkheads for added strength. After casting is complete, the block is CNC-machined, and here the same CAD tactic of "dynamic sectioning" that ensured adequate wall thickness during design of the block also helps achieve maximum precision during machining.

Up top, the strength of the head gasket seal is greatly improved thanks to a total of eight additional large head bolts per cylinder bank. Whereas factory LS blocks typically utilize only four large head bolts for each cylinder (making for a total of ten M11 bolts on each bank), the RHS LS Race Block uses six. All of this adds up to a total of eighteen large head bolts per cylinder bank, greatly increasing clamping of the cylinder head and thereby providing a more robust head gasket seal.

The cylinders themselves are stout as well. A Siamese bore is used to help accommodate this, but unlike some other aftermarket blocks, the water jacket encircles the bores as completely as possible (just like in the LS7). Press-in spun cast iron liners are super strong, and are claimed to be almost like a forging, as their casting process helps them receive the benefit of similar grain structure to that of a forged piece.

Despite all of these strength enhancements, Reese reports that the RHS block will weigh in at about 119 pounds, just a bit more than an LS7. And as just one more example of the engineered-in strength of the LS Race Block, rolled threads are utilized on every threaded hole, even those used to attach accessories. Now that's attention to detail!

Big-Cube Capability
Want additional inches out of your underhood beast? The RHS LS Race Block delivers. It's available in two deck heights: the standard 9.24-inch, as well as a 9.75-inch version (availability of even taller decks on a custom basis is pending). Taking a page from the "Olds Rocket Block" iteration of the SBC, a raised camshaft, along with the main oil gallery having been moved outward, allows up to a 4.60-inch stroke to be utilized without running into rod-to-block clearance problems, even with standard rod journal diameters. Unlike other aftermarket blocks, the ability to contain such a hefty stroke was not a design afterthought; it was intended from the very beginning. As to cylinder liner lengths, both standard deck (5.67/5.87-inch; same as the LS7) and tall deck (5.94/6.38-inch) versions are available, and big-inch builders know how critical this aspect can be to piston durability on long-stroke engines, where the piston can otherwise come too far out the bottom of the bore.

As for bore sizing, the RHS LS Race Block was designed to accommodate finished bore sizes ranging from 4.060 to 4.165-inches, and a thickness of 0.089-inch is maintained in those super-strong iron sleeves even at maximum bore-not to mention an additional .200 of aluminum behind it. Doing some simple math, it's easy to see that if you combine a 4.165-inch bore with a 4.60-inch stroke, you wind up with over 500 cubic inches of LS power!

0904gmhtp_13_z Rhs_engine_block Top_view 13/17

This view makes clear where the extra head bolts for each cylinder will be located on the block. The 5th bolt will screw into the outer edge of the block, while the 6th "bolt" will actually be a stud placed in the head, whose nut is inserted and tightened to the block through those large valley windows.

Oiling System & Crankcase Design
Priority main is the name of the game with the LS Race Block, and this type of oiling system pays dividends for engine component life by delivering oil first to the crankshaft, where it's needed for the main and rod bearings. The main oil gallery and lifter galleries are both a large 14.5mm in diameter, and it's a dry-sump-friendly design, too, with provisions for -12 AN fittings at both the front and rear of the main oil gallery on the driver side of the block. Brian Reese points out that these are direct feeds, so those utilizing a dry-sump system won't have to adapt through a small metric plug like on other blocks. It's also versatile in that one can use either the front or rear plug for an oil pressure source. Another feature designed for easy use of dry-sump systems is that the machined oil drains in the valley/lifter area can be tapped and plugged easily. Did we mention provisions for piston oil squirters (as in the LS9) are included as well? If used, they mount on one side of the block just under the bores.

Regarding pumping losses, bay-to-bay breathing is improved with increased window area and enlarged passages under the bores and around the caps compared to the LS7 and existing aftermarket blocks. Specifically, the passage under the bores is claimed to provide a 4-percent area increase in the center bulkhead over an LS7 block, and because the bay-to-bay window is the same on all cylinders, a 39 percent increase is seen at #2 and #4. Finally, the passage around the main caps provides a 7-percent increase in area over the LS7. This is all good news, as again, reduced pumping losses mean more horsepower available at the back of the crankshaft.

Conclusion
The RHS LS Race Block promises to be an impressive piece as-delivered, but we should note that there is also end-user leeway built into it. For example, the cam tunnel can accommodate 60mm roller bearing cams, and the lifter bores, while delivered at stock 0.842-inch, can be enlarged to accept a keyed 1.060-inch bushing. (And custom machining is available; "anything is possible," says Reese. "We are pretty flexible with our core," and they can accommodate just about any request given the time and an additional fee). And on a final note, RHS LS Race Block will easily work in just about any vehicle application one might imagine, as amazingly, it can accommodate both Gen III and IV knock sensors, cam sensors, and valley covers! Look for the RHS LS Race Block to debut under part numbers 54900 (9.750 deck, 4.165 bore), 54901 (9.750 deck, 4.125 bore), 54902 (9.24 deck, 4.165 bore), and 54903 (9.24 deck, 4.125 bore). Expect a final MSRP of about $4,500.00. That's a good deal for what promises to be an outstanding foundation for all-out LS engines.

Sources

RHS
Memphis, TN 38118
877-776-4323
http://www.racingheadservice.com
FAST
Memphis, TN 38118
877-334-8355
http://www.fuelairspark.com
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