In our last installment, we set out to build a really big LS engine. How big? Well, in this case a rather voluminous 490 cubic inches. Yep, that’s big-block cubes in a small LS package.
The first step in supersizing our LS dreams was to grab an RHS tall-deck block and punch the bores out to 4.165 inches. RHS raised the deck from 9.240 inches on their standard-deck LS Aluminum Race Block 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 the maximum 4.165-inch bore, yields an astounding 501 cubic inches (8.2L). This makes for a ton of torque potential in a package about the size and weight of an older LS1.
On our engine we went down a step and opted for a 4.500-inch stroke, which still penciled out to a massive 490 cubic inches. That stroke is hard on the rotating parts, so in went top-shelf goodies from Lunati in the short-block, even going so far as to have the pistons fully coated. To properly control the oil, the short-block was fitted with a Dailey Engineering dry-sump system and RHS’ new oil squirters.
With the short-block done, it was time to finish it up and slap it on the dyno. Chris Pollock at Evod Garage in Escondido, California, did the math and wrenching—both of which are critical when building engines that push the envelope such as this. Engines are air pumps, and this 490 moves a lot of air. We were working with the excellent dyno headers from Hooker, and although the 1 7/8-inch tubes were great for most engines, bigger tubes would have helped the mill exhale a bit easier. On the intake side, some port work on the RHS LS7 heads may have possibly helped shove in more atmosphere, but we wanted to stick with off-the-shelf parts.
Follow along as we finish up our big-inch LS and send it over to Westech Performance for some quality time on their SuperFlow 902 dyno.
01. Chris Pollock at Evod Garage in Escondido, California, filled our tall-deck RHS LS Race Block with all sorts of go-fast goodies. Fitted with a 4.500-inch Lunati Pro Series crank, Lunati I-beam connecting rods, and 4.165-inch Lunati pistons, this mill displaces 490 cubic inches! That’s a lot of displacement in a compact and lightweight package. The engine is also set up to run a true dry-sump system and incorporates RHS’ piston oil squirter kit.
02. When it comes to making power, heads are vitally important, but they can easily destroy your budget. RHS set out to design a strong-performing head that wouldn’t leave your wallet running on empty. Their LS7 Pro Elite 291cc CNC-ported heads (PN 54501-06STS) cost well under two grand each and are the first LS-style head to feature a raised intake runner design. The heads work with both stock and aftermarket LS7 intakes and valvetrain setups. They feature 12-degree valve angles and the unique 0.220-inch raised intake runners allow a better line of sight into the cylinders. The heads feature a six-bolt design for better head gasket retention. Chamber volume is 69 cc (which Chris at Evod measured out at 70.5 cc) and the stainless valves are 2.200-inch for the intake and 1.615-inch for the exhaust.
03. To seal the heads to the block we went with a pair of Fel-Pro PermaTorque MLS RHS gaskets (PN 26496L-041, 26496R-041). The 4.200-inch bore, 0.041-inch thick gaskets have a stated volume of 9.3 cc, which will net us a final pump-gas-friendly compression ratio of 10.64:1.
04. The six-bolt RHS heads were then mated to the six-bolt RHS tall-deck block. The extra bolts of this design really increase the clamping force, which is especially critical in boosted applications.
05. Tying the two together is the job of our ARP head studs (PN 234-4339). The large bolts were torqued to 90 ft-lb, while the smaller fasteners were taken to 28 ft-lb.
06. One way to fix the geometry problems of a large-lift cam is to switch to an adjustable shaft-mount rocker system like this kit from COMP (PN 1525). This 1.8:1 ratio rocker system is fully adjustable so the power of the camshaft can be precisely transferred to the valves. The roller rockers are made from high-grade aluminum while the shafts are 8620 hardened steel.
07. For this engine, we opted to try out MSD’s Atomic AirForce LS7 intake manifold (PN 2701). If you’re familiar with typical LS intake gaskets you’ll notice that these are much larger.
08. The taller deck of our RHS block meant that we needed spacers to get an LS7 intake to match up with the head ports. RHS offers some very nice ones for use with their line of intakes, but MSD’s intake gaskets are much larger than RHS’s and rode right on the edge of the RHS plates. To keep from having vacuum leak problems, we picked up a pair of these larger spacers from Turn Key Engines out of Oceanside, California.
09. The MSD Atomic AirForce line of intake manifolds are designed to flow lots of air, which is just what a 490ci LS needs. According to MSD, their bell-mouthed runner entrance maximizes airflow and minimizes shrouding. It also features a two-piece design to make it easier to port.
10. We chose a 103mm MSD Atomic LS throttle body (PN 2945) to match up with the 103mm opening on our MSD AirForce intake. The stainless shaft resists twisting for a more accurate TPS signal and it also rides on dual ball bearings for smoother operation. To finish off the throttle body, we ordered MSD’s TPS/IAC kit (PN 2942), which included both of the necessary sensors.
11. The MSD intake allows for the MAP sensor to mount in several locations. We chose the left rear corner, which necessitated drilling a small hole.
12. And with that, our 490ci RHS engine was ready to head over to the dyno to nail down some numbers. With some work, you can run aftermarket fuel rails on the MSD intake, but we opted for the easier route and went with an LS7 fuel rail from Chevrolet Performance.
13. To feed our 490 LS fuel, we installed eight 65-lb FAST fuel injectors (PN 30657-8) and secured them to the fuel rail using the GM locking clips.
14. Once on the Westech Performance SuperFlow 902 engine dyno, we added oil to the Dailey dry-sump system, connected the loom from our Holley Dominator ECU, and installed a set of Hooker LS 1 7/8-inch headers. An engine this big would benefit from larger-tube headers, but these were the best flowing headers we had on hand.
15. After tracking down a bad plug wire and doing some tuning, we were rewarded with a best pull of 700 hp (at 6,000 rpm) and 665 lb-ft of torque (5,200 rpm). The large stroke meant the hp numbers started to fall off after 6,300 rpm. Still, the displacement created massive amounts of torque across the entire pull, with over 500 lb-ft as low as 3,600 rpm!
16. People often get fixated on peak numbers, but there’s way more to it than that. Here’s our 490ci RHS engine compared to a recent 427ci LS7 build we did. On paper, the 660 hp of the LS7 seems fairly close to the 700 hp of our 490. After all, the difference in peak numbers is only 40 hp. But, when you look at the entire graph you can see how the 490 crushed the LS7 across the whole pull, in some places beating the torque of the LS7 by more than 80 lb-ft. Only after 6,500 rpm does the lighter rotating assembly (titanium rods, etc.) give the edge to the LS7. But up until then, the 490 just produces more power and torque across the graph.