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Big Displacement from a Small-Block Package with an RHS LS Block

Walking Tall: RHS’ LS block makes it possible to get big-block displacement from a small-block package

Jul 28, 2016
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Supersized fries and 32-ounce sodas seem to sum up society’s obsession with going big. Given this, it’s no wonder that engines, especially GM’s LS variants, have been creeping up in displacement. After all, the early LS engines were as small as 293 cubic inches (4.8L). The LS1 was 346 cubic inches, which grew into the LS2 at 364 cubes (6.0L) and then expanded again into the LS3 at 376 glorious cubes (6.2L). The biggest LS variant churned out by GM ended up being the LS7 at 427 cubic inches (7.0L). Four hundred and twenty-seven inches in a small-block-like package is pretty darn impressive, but the market demanded more. To feed this demand, companies like RHS came up with their own blocks to take displacement even further. The standard-deck RHS Race Block can accommodate a 4.165-inch bore along with a 4.250-inch stroke for a maximum displacement of 463 cubic inches—a crazy displacement number for something with the same external dimensions as that diminutive 293ci version. But what if you want even more?

Well, RHS has you covered with their tall-deck block. They raised the deck from 9.240 inches to 9.750 inches. That may not sound like a lot, but it allows for a much longer stroke—up to 4.600-inch. That stroke, combined with a 4.165-inch bore yields 501 cubic inches (8.2L) of goodness. That displacement is big even in the world of big-blocks and it’s all in a package roughly the same size as, but lighter than, a traditional Gen I small-block Chevy.

The RHS block’s cam is raised, and their engineers spent considerable effort reworking the internal dimensions to accommodate spinning cranks and flying rods. They also addressed oil control and incorporated features like motor plate race mounts for the hard-core crowd and provisions to easily add a dry-sump oiling system.

We built a big-inch standard-deck RHS block before and were happy with the numbers so this time we wanted to have a go at the tall-deck version. We settled on a bore of 4.165-inch and a stroke of 4.500-inch for a final displacement of 490 cubic inches.

A big stroke is hard on parts so we went with top-shelf rotating parts from Lunati and a set of RHS’s new LS7-style heads. Top-quality parts are a waste of cash unless put together the right way, so we hit up the meticulous engine building services of Chris Pollock from Evod Garage in Escondido, California.

Given the huge stroke, we took advantage of the RHS block’s oiling provisions and worked a Dailey Engineering dry-sump system into the equation. Not only would this keep all the parts properly oiled, it has the advantage of helping relieve some of the excessive crankcase pressure.

Nothing about this build is “budget,” but it shows what’s possible in today’s aftermarket. It’s also a complicated build so we’ve broken it down into two parts. The first will cover the short-block and in the second installment we’ll assemble the top end and get it to Westech Performance for some quality time on their Superflow 902 dyno.


01. The RHS LS Aluminum Race Block (PN 54900U) really is a thing of beauty, but even though it looks great, the design is all about function. Their Clean Cast Technology gives the block an excellent finish quality, and for strength they use heavy-duty A357-T6 aluminum. The block is also dry-sump friendly with provisions for large -12 AN front and rear side feeds. Each block is CT-scanned by RHS to make sure it is as perfect as humanly possible.


02. The Siamese-cast bore walls can go from 4.100 to 4.165 inches and have press-in spun-cast-iron liners (5.87 inches for standard and 6.38 inches for tall decks). RHS also improved bay-to-bay breathing compared to LSX and LS7 blocks, and for added stability, the main caps have dowels. Wanting big displacement, we opted for RHS’ tall-deck (9.750-inch) version, which allows for a whopping 4.600-inches of stroke!


03. Oil is life, so in addition to priority main oiling, RHS designed the block to use piston oil squirters. These weren’t available the last time we built an RHS-based LS engine so we were eager to give them a go. The block was already tapped so we just had to use a 5/16-inch bit to drill out each of the four passages (each squirter supplies two pistons).


04. To us, street car is synonymous with hydraulic roller in terms of camshafts. At 490 ci we were able to run a pretty stout bumpstick without worrying about killing the idle characteristics of the engine. After talking with Evod’s engine builder Chris Pollock and the go-fast geeks at COMP, we came up with cam specs of 263/275-degree duration, 0.624-inch lift, and 112 LSA (installed on a 108.5 intake centerline). However, our RHS LS7-based heads use 1.8:1 ratio rockers so the lift is actually 0.661 inch. Stuffed into a smaller LS engine this would be a huge cam, but in our big-cube, tall-deck RHS engine it’s right at home.


05. Another part we would describe as beautiful would be this Lunati Pro Series crank (PN 60845001). Forged from 4340 certified steel, this American-made and -machined crank will handle the tons punishment planned for its future. The journal radii are ground to 0.140 inch. Roundness of each journal is 0.0001-inch or less, and each rod journal incorporates a lightening hole to reduce inertia weight. To hit our 490-inch displacement goal, its stroke is 4.500-inches.


06. In engine building, a little bit is a lot. While a 4.000-inch crank is barely bigger than stock, an extra half-inch of stroke is a really big deal. In the case of our 4.500-inch crank, we had the assembly balanced at Lunati where the crank required nearly 5 inches of Mallory. Tungsten is very dense, but it’s also difficult to work with, so it’s mixed with other metallic elements to create the alloy marketed as Mallory. The difference in weight between the Mallory and the original steel is roughly 2:1. So the Mallory slug added to the crank is about twice the weight of the steel it replaced.


07. After giving the Clevite bearings a thick coat of assembly lube, Chris set the Lunati crank in place and installed the billet RHS caps with the included ARP fasteners. For serious power applications, there’s enough material to accommodate main studs up to 1/2-inch. Once the crank was in place, Chris checked the crank thrust, which came in at an acceptable 0.002-inch.


08. The RHS block does require a proprietary brass cam thrust plate, but they are nice enough to include it with the block.


09. The forged pistons that came with the Lunati rotating assembly were made by Icon and had a -24cc dish. They came uncoated, so we sent them over to Embee Performance in Santa Ana, California, for some of their specialized coatings. The skirts received a coat of anti-friction material while the tops received a thermal barrier coating. This thermal barrier will help keep heat out of the piston and in the combustion chamber where it belongs. The skirt coating added about 0.0006 inches to the diameter of each piston. Combined with our piston being 0.005 in the hole and a 0.041-inch compressed gasket, we will be at a compression ratio of 10.64:1 with our 70.5cc chamber RHS heads. Yes, that’s a lot of math.


10. Packaged with our Lunati crank was a set of their 4340 I-beam rods (PN JP6300-8). And like the crank, it’s a shame they will be hidden inside the engine. The rods are heat-treated, stress-relieved, shot-peened, and magnafluxed to ensure the highest level of quality. 4340 forged steel is extremely strong and often used in commercial and military aircraft, as well as automotive racing applications. It also retains excellent fatigue strength. Included with the rods were ARP 2000 rod bolts. Due to the long stroke of the crank, we went with 6.300-inch rods instead of the more common 6.125-inch version.


11. The parts comprising the RHS oil squirter system are pretty cool, and it’s easy to see why they took a while to come to market. The stainless “bolt” has a lot of machine work involved and was gun-drilled and then plugged to get the oil movement right. The oil emitter ring has two nozzles to supply a spray of oil to the bottoms of two pistons. This oil spray helps cool the pistons to help control detonation. While it’s particularly valuable in boosted applications, we decided it had benefits in our application as well.


12. Here’s one of the four oil squirter assemblies. The O-ring goes on the bottom to seal the ring to the block.


13. And here it is in place in the RHS block. In essence, the emitters are controlled oil leaks, and even though the tubes look tiny, they produce quite a spray of oil into the cylinder bore.


14. With the oil squirters in place, we could slide the piston/rod assemblies into their home using an ARP ring compression sleeve.


15. Chris then torqued the ARP 2000 fasteners to 70 ft-lb. There’s a lot of fastener goodness on display in this picture.


16. Here we had a bit of a problem. We needed a 4x, three-bolt cam sprocket with a double-roller timing chain long enough for the raised cam design of the RHS block (one link longer). Surprisingly, COMP didn’t offer that combination. After talking with them a bit, we figured out that they made all the parts we needed, so we went a la carte. Hopefully, they will be offering this kit for those of us who prefer a three-bolt cam over the newer single-bolt design on our RHS block builds.


17. With LS engines you can usually cheat and skip degreeing the camshaft, but that’s not really the right way to build a quality engine. At TDC, the piston was found to be 0.005-inch in the hole. As for the cam, it was installed straight up and came in right at the 110-degrees noted on the cam card.


18. As previously stated, Chris had originally installed the cam at the recommended 110-degrees, but when checking the piston-to-valve clearance, he only had 0.092-inch clearance. This was a bit too tight for his liking so he installed the cam at 108.5-degrees, which opened up the distance to an acceptable 0.121-inch. Attention to detail and the checking of tolerances is what makes for a successful engine build.


19. We sealed up the front of the engine with COMP’s timing cover (PN 5496). This cover is great on many levels. First, it easily accommodates double-roller timing chains, plus it can work with standard and raised cam blocks. It can also accommodate a timing pointer. The cog drive is for the Dailey Engineering dry-sump pump.


20. Yep, our 490 LS is running a Dailey Engineering dry-sump oil system. The pan is part of their integral Signature Series. The oil pump bolts directly to the oil pan, thus eliminating the -AN lines between the pump and pan. All scavenge lines are internally machined into the oil pan, saving weight and the cost/clutter of external lines. Our right-side mounted system utilizes a three-stage pump. In addition to moving oil, the system also helps remove crankcase pressure.


21. These captured link-bar race lifters from COMP (PN 15956-16) were designed to perform better at higher engine speeds. They do this by cutting down on power loss and valvetrain failure by limiting the lifter’s internal piston as they are pumped up. The link-bar design is far more stable than the plastic lifter trays found in factory LS engines. The lifters came REM-finished and black oxide-coated.


22. And that marked the end of our short-block build. Next up, we’ll install the top end of the 490ci LS and get it over to the dyno at Westech Performance to see what it will put out.


Comp Cams
Memphis, TN 38118
Westech Performance
Mira Loma, CA 91752
Racing Head Service
Memphis, TN 38118
Embee Performance Coatings
Santa Ana, CA
Memphis, TN 38118
Evod Garage
Ventura, CA 93003



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