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RHS LS Aluminum Block - Bigger On The Inside Part 2
Sep 1, 2011
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RHS LS Aluminum Block - Bigger On The Inside Part 2
1. If you want to make good power, you’ll need a killer set of heads. These rectangular-port LS3 12-degree heads have 270cc intake ports and are compatible with the six-bolt design of our RHS block. The design is somewhat unique since it utilizes Gen IV LS7 rockers but accepts LS3/L76 intake manifolds.
2. These fully CNC-machined heads (PN 510-304, $1,599 ea.) use a 2.200-inch intake and 1.600-inch stainless hollow stem valves and feature thick .750-inch decks. They are also set up to work with big-bore (4.125-inch or larger) applications like ours.
3. Most manufacturers of high-end heads provide flow numbers, but it’s always nice to check it yourself if you can. Tom Nelson, owner of Nelson Racing Engines in Chatsworth, California, has a sweet Superflow flow bench, so we decided to see if there were any gains to be had by fussing with the heads.
Going with the Flow Nelson decided to try a 30-degree back-cut on the valves. As he told us, “Air is a tricky thing. The goal in a port is to control the air around the valve. As a matter of fact, at high lifts, if you were a mini person standing next to the valve stem there would be very little air passing you next to the stem. The busy areas are on the seat and valve angle. The way we cut the back of the valve we were able to bend and direct the air in an efficient path around the valve.” The Mast heads flowed an incredible 390 cfm at .750-inch, but because the lift of our cam maxed at .624-inch, we would never see a benefit. The back-cut traded some flow at the higher lifts for more air down low where a street engine like ours spends most of its life. Yeah, it’s a trade off but one we felt suited how the engine would be ran.
5. After messing with the heads, we were ready to jump back onto the short-block. We installed all the ARP head studs to show just how many fasteners are involved with the six-bolt arrangement. The extra strength provided by the extra fasteners is especially important in boosted or nitrous applications.
6. Before installing the heads, we dropped in these COMP captured-link-bar roller lifters. (PN 8957-16, $525). The RHS block doesn’t utilize the plastic LS lifter trays so lifters with a link bar need to be used.
7. When we started this build we didn’t realize that the RHS block calls for a specific gasket to work with its interlocking sleeve design. Because of this we used the common .050-inch GM MLS gasket thickness in our math for compression. The Fel-Pro-made RHS gasket (PN 549402-L(R), $140 each) comes in with a compressed thickness of .036-inch, which bumped our compression up a bit. This is important to keep in mind when ordering pistons.
8. When doing an engine build it’s critical to check the piston-to-valve clearance. Assumptions made here can end up costing big bucks when a valve crashes into a piston. As Nelson explained, “Piston-to-valve clearance should be .100-inch on the exhaust and .080-inch on the intake side at a minimum. Our tightest measurement came in at .150-inch, so we were good to go.”
9. The Mast Motorsports heads utilize LS7-style rockers, and at the time of our build there really wasn’t an aftermarket option, so we contacted Ed Doyle over at CHE to build us a set of their bushed rocker arms. CHE takes the factory rocker arms, removes the possibly problematic needle bearings and bushes them. According to Ed, “This has the added benefit of creating a stronger unit with better load characteristics and a rocker with a greater service life even under extreme conditions.”
10. The sixth head bolt was a real pain to secure. The problem is that the nut is right up against the block making it impossible to get a closed-end wrench onto it. An open-end wrench would make things easy, but that’s a “no-go” with a 12-point nut like what was in the ARP kit. Our solution was to grind down a cheap 3/8-inch wrench as a sacrifice to the engine gods. We sent ARP a note that life would be easier if these were six-point nuts.
11.To keep the black gold flowing through our mill, we slapped on this high-volume Moroso oil pump (PN 22120, $175). Besides putting out large volumes of oil, the design has the forward-facing bolts inset into the face. This makes running a double-roller timing chain much easier since you won’t need to shim out the timing cover for clearance.
12. Having the oil pickup properly located is imperative to making sure you end up with happy oil pressure readings at all rpm levels. If the pickup is too close you’ll starve the engine at higher rpm and if too far you can suck in air during hard turns. Using some putty we found our pickup from Autokraft fell right in the .25- to .50-inch range.
13. The steel 5.5-quart oil pan from Autokraft ($400) featured a four-corner trap door baffling system. This road race–style arrangement will make sure the pickup is always submerged in oily goodness.
14. One thing we really liked about the Autokraft pan was the thick steel flange that is less likely to warp and leak. It came to us with a billet oil filter adaptor, which we decided to use to make life easier on the dyno. For the car, we will switch over to a Canton adaptor that will hook up to our remote oil filter and cooling system.
15. At 461 ci, our LS engine requires a lot of atmosphere to keep it happy, so we topped it with a 102mm Fast LSXr intake manifold (PN 146102, $950). FAST really stepped it up with this offering by incorporating longer, less restrictive runners. To get even more air though this polymer intake, Nelson broke out the dremel and port matched it to the Mast heads.
16. And just like that, our long-block was done. On Gen IV LS engines, the front cover port for the cam sensor needs to be modified and raised up 0.388 inch to accommodate the raised cam. RHS is working on a new two-piece cover that won’t need to be modified. On tall-deck blocks, both Gen III and Gen IV cam sensors require no modification.
17. With the engine off the stand and in a cradle, we were able to install the two rear plugs (included in the kit) into the RHS block. The RHS block ditches GM’s “barbell plug” and replaces it with a stepped NPT plug. This eliminates the restriction caused by the barbell.
18. The rear cover is specific to the RHS block and is included with the kit. Rather than a gasket like the GM version, it utilizes two O-rings to seal. With the O-rings in place, we installed the rear cover using ARP bolts from our LS accessory fastener kit and torque them to 18 ft-lbs.
19. To complete our fuel system, we went with a set of billet fuel rails (PN 146027-KIT, $188) and 42-lb, LS1-style, injectors (PN 304200, $660) from FAST.
20. We hauled the engine over to Westech Performance for some quality time on their Superflow 902 dyno. For the test we used 91-octane pump gas and a Meziere electric water pump. Since we can’t run a drive-by-wire throttle body on the dyno, we went with a FAST 102mm mechanical version.
21. After eleven pulls worth of adjustments and tweaks to the computer program, we were rewarded with the best pull of the day. The peak power of 720 hp at 6,300 rpm and 662 lb-ft at 5,300 rpm should be more than enough to propel our ’68 around the track. We were especially happy with how the 461ci small-block LS made over 400 lb-ft of twist way down at 2,500 rpm and by 4,000 rpm was churning out over 600 pounds. Even though peak power was at 6,300 rpm, we were getting just over 700 hp at 6,700 rpm with no hints of valve float.
22. On the dyno we ran a Meziere electric pump, but on the street we wanted something mechanical in nature, so we went with a belt-driven race pump. These pumps were torture-tested on the Baja 1000 and are built to handle almost anything. On the top end, this pump moves well over 150 gpm in free-flow and has been dyno-proven to boost both horsepower and torque. The power gains are due to a more efficient impeller and cavity design. This allows the pump to spin faster without cavitating.
23. With over 660 lb-ft of torque from the new engine, we were a bit concerned with our old single-disc clutch, so this was the perfect excuse to upgrade to Centerforce’s new twin-disc unit. This is the same clutch we installed in our ’10 SS Camaro project car back in the May ’11 issue.
24. As they say, “third time’s a charm.” Well, in our case it was the fourth, but we plan on this 461 staying in our Bad Penny project car for the foreseeable future. What’s nice is that the 461 RHS engine was an easy swap from the previous stroker LS2.
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