1968 Camaro 461-Inch RHS LS Engine Build and Dyno

Early Adopter: A fresh rehash of a 461-inch RHS LS engine

 Getting in on the ground floor of new automotive technology is always cool, but there’s also a downside. Namely that later versions typically have all the bugs worked out and there are far more associated parts available. Back in 2010, we built a 461-inch LS engine for our 1968 Camaro project car Bad Penny. The build was based around RHS’s “new” race block. Yep, this badass block let us shoehorn 461 inches of glorious displacement within the confines of a block no larger than a typical LS1. And, while we never found any “bugs” with the block, COMP/RHS has since released a lot of supporting parts that would have made our build better.

The block we have features a raised cam tunnel, and RHS spent considerable effort reworking the internal dimensions to accommodate the longer rods and crank spinning about. They also addressed oil control issues found in stock LS blocks and added provisions to easily incorporate a dry-sump oiling system. For those that don’t mind the external dimensions bumping up a bit, RHS also offers a tall-deck version that is engineered to accept up to a 4.600-inch crank. Combined with the RHS block’s maximum bore of 4.165, it has the potential for 501 cubes (8.2L). In our case, the standard-deck block made more sense since we would be able to reuse our custom headers.

But, as any engine builder will tell you, a big stroke is inherently hard on parts, and for nearly 15,000 miles we mercilessly beat the ever lovin’ snot out of the 461. The engine happily accepted our abuse, but the thin rings necessitated by the short, stroker pistons, started to wear and let compression out of – and oil into – the combustion chambers. Not a good combination for performance. Given this, we decided to pull the 461 apart, do a rebuild, and see how everything was holding up.

Rhs 461 Ls Engine Build Dyno Wiseco Forged Piston 02
1. The rings in our hard-run 461 were shot, but the pistons were in pretty good shape. After cleaning them up, we found a few signs of detonation, so we decided to drop the compression a bit to compensate for our cruddy California gas. We also felt the Armorglide antifriction skirt coating on the Wiseco pistons held up pretty well to the tortures of the long 4.250-inch stroke. The pistons are off-the-shelf 4.155-inch bore, 2618 forged pieces with a -8cc dish.
Rhs 461 Ls Engine Build Dyno Coated Piston 03

2. To make our pistons “better than new,” we sent them over to Embee Performance in Santa Ana, California, for some of their specialized coatings. The skirts received a fresh coat of antifriction 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 coating added about 0.0006-inches to the diameter of the piston.

Rhs 461 Ls Engine Build Dyno Block Hone 04

3. We sent the block and rotating parts to Total Performance in Santee, California, where they found that the bores were in excellent condition and only needed a very light hone. This meant we could keep our pistons, saving us a nice stack of cash.

Rhs 461 Ls Engine Build Dyno Comp Camshaft 05

4. Our old COMP cam was pretty tame (given our displacement) so we decided to stay in the ballpark in terms of overall size on the new stick (PN 54-474-11). We bumped the duration from 247/263 (at 0.050) to 251/267 and the LSA went from 114 to 115 (installed at 112 intake centerline), but the lift stayed the same at 0.624-inch. Keep in mind that the 1.8:1 LS7 rocker ratio bumps that lift up to around 0.661-inch. A bigger cam could definitely net us more power, but street manners are worth a few ponies.

Rhs 461 Ls Engine Build Dyno Main Bearing 06

5. Chris Pollock over at Evod Garage found some chatter marks on our main bearings, which meant our clearances were a bit loose. Instead of trying to fix it with thicker bearings we had Total Performance machine/shave the main caps and then line-hone the block. Sure, it costs more to do it this way, but the right way typically isn’t the cheapest option. For bearings, we went with Clevite MS-2188HX pieces and Chris double-checked that everything was perfect before we dropped in the crank.

Rhs 461 Ls Engine Build Dyno Lunati Crank 07

6. The Lunati Signature Series crank (PN JP711ER) was badass five years ago, and it still is. Forged from 4340 certified steel, this American-made and machined 4.250-inch stroke crank will live forever at our power levels. We had the crank massaged and polished at Total Performance.

Rhs 461 Ls Engine Build Dyno I Beam Rod Lunati 08

7. The rods, like the crank, were top-of-the-line offerings from Lunati. These 4340 I-beam rods (PN JP6125-8) had ARP 2000 rod bolts. On the big end they were out of round a bit so Total Performance cut down the caps and honed them back to spec.

Rhs 461 Ls Engine Build Dyno Short Wiseco Piston 09

8. Chris then file fit all the rings (0.018-inch top and 0.022 second) and mated them to the rods with a fresh set of Wiseco wire locks.

Rhs 461 Ls Engine Build Dyno Summit Piston Install Sleeve 1010/31

9. The thin (1.2mm first and second, 3.0mm oil ring), moly-faced, ductile-iron rings are easy to bend on installation, so the best way of getting them in place was by using a specialized installation sleeve. We picked up this tapered 4.155-inch piece (PN SME-904155) from Summit racing for around $30.

Rhs 461 Ls Engine Build Dyno Thrust Plate 11

10. To secure the cam, we installed the RHS proprietary brass thrust plate. We also stuffed in a new O-ring (PN 549204-1). The RHS block makes extensive use of O-rings, and replacements are readily available through RHS.

Rhs 461 Ls Engine Build Dyno Comp Double Roller Timing Chain 12

11. The raised cam of the RHS block meant it required a longer timing chain (one extra link). In 2010, the only offering out there was a single roller, so that’s what we ran. Well, today RHS offers several choices, including this three-key double-roller (PN 3154) with the correct length chain. The single-pulse cam sprocket is because our Camaro runs an early 24x reluctor-based computer.

Rhs 461 Ls Engine Build Dyno Cam Degree 13

12. It was then time to degree the cam. The card called out for installing the 115 LSA camshaft on a 112.0 intake centerline and the three-key sprocket let us get to 110.5, which was close enough.

Rhs 461 Ls Engine Build Dyno Oil Pump Install 14

13. And here’s the right way to install an LS oil pump. Chris explained that the pump has a bit of play and if it’s just “slapped on,” then it will likely be off center and end up rubbing the crank sprocket. His solution was to pull off the front plate and use a feeler gauge to get it centered just right. You can also see the timing cover kit’s small pump spacers, which allowed the pump to clear the wider chain without grinding.

Rhs 461 Ls Engine Build Dyno Short Block Ati 15

14. Another item that didn’t exist when we first built the engine was this sweet COMP timing cover (PN 5495). In addition to having added clearance for double-roller timing chains, it allows for repositioning the cam sensor for better reading of the raised cam. For easier cleaning we had the cover powdercoated charcoal grey. This sure beat the old suggestion of cutting and welding a stock cover to get proper sensor positioning. We also installed the ATI Super Damper that has served us well for going on eight years now.

Rhs 461 Ls Engine Build Dyno Ls7 Pro Elite Head 16

15. Heads are something vitally important to how a given engine will perform, but they can also easily consume much of your budget. Will a set of $6,000 heads outperform a set that costs thousands less? Yeah, but then again they should. RHS set out to design a strong performing head that wouldn’t leave your wallet a smoldering, empty mess. Their LS7 Pro Elite 291cc CNC-ported heads (PN 54501-06STS) cost well under $2,000 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 and the stainless valves are 2.200-inch for the intake and 1.615-inch for the exhaust.

Rhs 461 Ls Engine Build Dyno Piston To Valve 17

16. Before committing to the install, Chris wanted to verify that we had plenty of piston-to-valve clearance. So he installed light springs and bolted on a head using shims to simulate head gasket thickness. The intake had 0.245-inches of clearance to the piston while the exhaust was at 0.255-inch; more than enough.

Rhs 461 Ls Engine Build Dyno Pushrod Measure 18

17. This was also a great time for us to figure out what length pushrods we would need. The right length ended up being 7.800 inches on the intake and the exhaust. With info in hand we ordered up the right COMP pieces from Summit Racing.

Rhs 461 Ls Engine Build Dyno Cometic Gasket 19

18. OK, part of the reason our compression was so high was that we misused a 0.051-inch (compressed) head gasket when building the original engine. It turned out that the RHS recommended gasket came in at 0.036 inches compressed. That in turn jacked the compression up to nearly 11.9:1. RHS didn’t offer a thicker gasket, but we did find some from Cometic that had a compressed thickness of 0.051-inch. The only difference we found between the recommended gasket and the Cometic were that these two water passages were larger on the Cometic gaskets. RHS explained that they made them smaller to better seal to their block, but after test-fitting them on the block we felt the Cometic pieces (PN CAGC5935-051 and CAGC5936-051) would seal fine – and besides, we really needed to drop the compression.

Rhs 461 Ls Engine Build Dyno Rhs Ls7 Head 20

19. It was then time to install the RHS LS7 heads. With the 69cc chamber volume our new compression should come in right at 11.54:1. This will cost us power, but reliability and longevity are far more important.

Rhs 461 Ls Engine Build Dyno Plug Clearance 21

20. We found that the reluctor wheel on the crank was barely hitting (and self clearancing) a small aluminum plug near the back of the block. To ensure it didn’t happen again we used the witness mark as a guide and knocked the edge off the plug. We also replaced the O-rings on all of the RHS oil and water gallery plugs.

Rhs 461 Ls Engine Build Dyno Autokraft Oil Pan 22

21. The oil pan will be the same tried-and-true, four-corner-trapdoor, baffled 5.5-quart wet-sump pan we’ve always run. The Autokraft pan has a thick steel flange so it won’t warp and even though it can be run with a billet oil filter adapter we opted for a remote filter, which increases volume and makes plumbing in a cooler easier. Our car has pulled hundreds of high-g (over 1.2) turns and has never had an oil issue. We cleaned up the old pan and had the outside powdercoated silver since it was beat down by all the road miles.

Rhs 461 Ls Engine Build Dyno Autockraft Pickup 23

22. The Autokraft pickup tube did give us a bit of trouble. The spacers moved the oil pump forward to clear the timing chain. This meant the pickup tube moved forward and didn’t line up with the rear main stud. And the hole was also too small for the ARP stud. After some time with a drill, and a little hammer therapy, all was good to go.

Rhs 461 Ls Engine Build Dyno Comp Short Travel Lifter 24

23. These captured-link-bar hydraulic lifters from COMP (PN 15956-16) are great for the money. Link-bar style lifters are needed on RHS blocks since there’s no provision for the plastic lifter trays found on OE LS blocks. We chose short-travel style since they cut down on power loss and valvetrain failure by limiting the lifter’s internal piston movement as they are pumped up by oil pressure.

Rhs 461 Ls Engine Build Dyno Lsxr Ls7 Intake Black 25

24. To feed atmosphere to the heads, we opted for a FAST LSxR 102mm LS7 intake. It will flow great and we’re digging the new black cover over the old fingerprint-attracting grey that they used to come in.

Rhs 461 Ls Engine Build Dyno Rocker Stand 26

25. The high lift of our old cam, combined with using GM LS7 rockers, was causing the tips of the rockers (and ends of the valve stems) to get chewed up a bit. Given this, we decided to switch to a roller tip shaft rocker. To accommodate the rockers we had to have the pad area cut down 0.030-inch. With that done we attached the rail using the supplied ARP fasteners.

Rhs 461 Ls Engine Build Dyno Comp Shaft Rocker Td Adjust 27

26. One way to fix the geometry problems of a high-lift cam, is to switch to a shaft-mount rocker system (PN 1525). This 1.8:1 ratio COMP kit is fully adjustable, so the motion of the camshaft can be precisely transferred to the valves. With the rail in place, we could then install and adjust the rockers. The roller rockers are made from 2014 aluminum while the shafts are 8620 hardened steel.

Rhs 461 Ls Engine Build Dyno Fast 60 Lb Fuel Injector Minimin 28

27. To complete our fuel system, we went with a set of billet fuel rails (PN 146027-KIT) and 60-lb, LS1-style injectors (PN 304200) from FAST.

Rhs 461 Ls Engine Build Dyno Westech Dyno Superflow 29

28. With the engine together, we hauled it over to Westech Performance for some quality time on their Superflow 902 dyno. For the test we used 91-octane Rocket supplied 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.

Rhs 461 Ls Engine Build Dyno Westech Dyno Sheet Superflow 3030/31

29. After nine pulls worth of adjustments and tweaks to the computer program we were rewarded with the best pull of the day of 674 hp at 6,100 rpm and 617 lb-ft at 4,700 rpm. We were especially happy with how the 461-inch LS made over 450 lb-ft of twist way down at 3,000 rpm and at 5,800 rpm was still pumping out over 600 lb-ft. Even though peak power was at 6,100 rpm we were still well over 650 hp at 6,500 with no hints of valve float.

Rhs 461 Ls Engine Build Dyno Comp Piston Oil Squirter 31

Controlled Oil Leak

Oil is life, so in addition to priority main oiling, RHS also designed their block to use piston oil squirters. These weren’t available when we built the engine, but they are now and can really be of benefit on boosted engines where keeping the pistons a bit cooler is critical. On our naturally aspirated engine there wouldn’t have been much benefit, so we left them off.

Going With The Flow

Of course, there’s more to a head than just its advertised runner size. The best way to scope out how a head should perform is to send it to a flow bench where it can be tested. Of course, there’s a host of other forces at play (such as velocity, chamber design, etc.) that affect how a head performs, but flow numbers are handy for getting a general idea of how a head works. This test, carried out at Westech Performance, was done at 28-inches of water.

Flow Numbers for RHS LS7 heads
Lift Intake Exhaust
0.1 71 52
0.2 152 106
0.3 228 158
0.4 281 193
0.5 324 220
0.6 360 230
0.7 385 238



Leave a Reply