RHS LS1 Head Upgrade - Steps Continued and Dynos

Sucp 1108 Rhs Ls1 Upgrade Swap Til Ya Drop 002

Before we could compare the RHS 225 LS1 heads to a set of stockers, we needed a suitable test motor. While the RHS heads were certainly capable of supporting impressive power levels (likely above 600 hp on the right normally aspirated application), we decided to build an engine more representative of the average enthusiast. To that end, we assembled a 383 stroker by machining a production 5.3L block to accept both a 4.0-inch stroker crank and a set of 3.902-bore forged pistons. The 4340 forged-steel stroker crank and matching 6.20-inch rods came courtesy of ProComp Motorsports, while the forged pistons came from Probe Racing. Additional power was available with a flat-top design (thanks to higher compression), but future turbo plans limited our choice to a 21cc dish piston to keep the static compression near 9.5:1.

L&R Automotive was responsible for boring, honing, and assembly of the finished 383 short-block. Our cam choice was in keeping with our mild street-motor motif. The dual-pattern XE265HR cam (XFI RPM Series) from Comp Cams offered a .522/.529 lift split, a 212/218 duration split, and an idle-friendly 114-degree lobe separation angle. We have run this cam many times in the past with excellent results. In every instance, the XE265HR improved the power output over the stock cam through the entire rev range.

More importantly (for daily street use), the Comp cam did so without sacrificing idle quality or drivability. There are wilder (and more powerful) cam choices, but the XE265HR is one heck of a good street cam. The hydraulic roller cam was combined with a new set of lifters and hardened pushrods from Comp Cams. The buildup also featured ARP head studs, Fel Pro head gaskets, and a new Sealed Power oil pump and timing chain set. The stock oil pan and windage tray were replaced by a new setup from Moroso, which included a remote oil filter.

The 383 was configured on the engine dyno with a FAST management system, a Meziere electric water pump, and a set of 1-3/4-inch long-tube headers from American Racing. The induction system consisted of a Fast LSX intake and throttle body fed by a set of 36-pound injectors. Prior to testing, the motor was broken in with conventional motor oil, but we made the switch to 5W-30 synthetic (both from Lucas Oil).

Run with stock LS1 heads, the mild 383 produced 465 hp at 5,500 rpm and 485 lb-ft of torque at 4,400 rpm. Swapping out the stock heads for the RHP Pro Action 225 heads increased the peak numbers to 506 hp at 5,700 rpm and 503 lb-ft of torque at 4,700 rpm. You know you have done well when your head swap improves the power output through the entire rev range, and that is exactly what happened. Torque production from our mild stroker now exceeded 450 lb-ft from 3,600 rpm to 5,800 rpm, making one sweet (and effective) torque curve. The best thing is that our RHS heads have plenty of flow in reserve, giving them the ability to support future (wilder) combinations. Should you see the need to install wilder cam timing, a blower, or nitrous, you have all the cylinder head you need.

4 Rather than set up a maximum effort killer, we decided to assemble one that better represented the typical street/performance application. To that end, we installed a Comp XE265HR cam. The mild XFI-series cam offered a .522/.529 lift split, a 212/218 duration split, and a wide 114-degree lobe separation angle.
4 Rather than set up a maximum effort killer, we decided to assemble one that better repr
5 Both heads were run with the same set of stock LS1 rockers, though roller rockers (especially with 1.8 ratio) would certainly improve the power output.
5 Both heads were run with the same set of stock LS1 rockers, though roller rockers (espe
6 To ensure we did not restrict the heads, we teamed the FAST LSXR intake and 101mm throttle body with a set of 36lb injectors and billet fuel rails.
6 To ensure we did not restrict the heads, we teamed the FAST LSXR intake and 101mm throt

7 American Racing supplied these 1-3/4-inch long-tube headers for our LS test motor. The high-quality stainless steel headers were run with 18-inch collector extensions but no mufflers.
7 American Racing supplied these 1-3/4-inch long-tube headers for our LS test motor. The
8 Equipped with stock LS1 heads, the mild 383 produced 465 hp and 485 lb-ft of torque.
8 Equipped with stock LS1 heads, the mild 383 produced 465 hp and 485 lb-ft of torque.
9 The RHS Pro Action 225 heads derived their name from the intake port volume of 225cc. Though the as-cast heads featured no CNC porting, the flow rates were impressive nonetheless.
9 The RHS Pro Action 225 heads derived their name from the intake port volume of 225cc. T

10 The RHS Pro Action 225 heads were supplied fully assembled with a spring package that allowed us to not only run our .529 lift cam (actually up to .600 lift), but safely rev the motor past 6,000 rpm.
10 The RHS Pro Action 225 heads were supplied fully assembled with a spring package that
11 Featuring a 2.05/1.60 valve combination and highly efficient, 62cc (as-cast) combustion chambers designed to improve both airflow and flame propagation, the Pro Action heads vastly outperformed the stock LS1 units.
11 Featuring a 2.05/1.60 valve combination and highly efficient, 62cc (as-cast) combustio
12 Exhaust flow was maximized through 80cc (as-cast) exhaust ports. Note that the RHS heads featured provisions for the factory ECT sensor making them a direct bolt-on.
12 Exhaust flow was maximized through 80cc (as-cast) exhaust ports. Note that the RHS hea

13 Replacing the stock heads with the RHS Pro Action 225 heads resulted in a sizable jump in power. Equipped with the RHS heads, the 383 thumped out 506 hp at 5,700 rpm and 503 lb-ft at 4,700 rpm. Torque production exceeded 450 lb-ft from 3,600 rpm to 5,800 rpm.
13 Replacing the stock heads with the RHS Pro Action 225 heads resulted in a sizable jump
14 Power Graph 1: LS Head Test - Stock vs. RHS 225 As Cast
What was surprising about this test was that despite a lack of CNC porting, these as-cast heads from RHS offered the kind of power gains we normally associated with fully-ported heads. Where the stock 5.3 produced 465 hp and 485 lb-ft of torque, the RHS-headed combo stepped these numbers up to 506 hp and 503 lb-ft of torque. Every bit as important was the fact that the head swap improved the power output throughout the rev range—always a good sign.
14 Power Graph 1: LS Head Test - Stock vs. RHS 225 As Cast What was surprising about t