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Complete Chevy Big Block Build & Testing - Action-Packed Big-Block Test

We Pick Up 116 HP With A Simple Swap To RHS Pro Action Heads, Edelbrock Intake And A Lumpier Comp Cam.

By Richard Holdener, Photography by Richard Holdener

Compared to the stock peanut-port castings, the RHS 320cc BBC heads were a serious step up the performance ladder. To take full advantage of the airflow offered by the RHS aluminum heads, we swapped out the mild, torque oriented XE256H cam and replaced it with a more performance oriented XE284H grind. The XE284H hydraulic flat-tappet offered 0.574/0.578 lift split, a 240/246 duration split (at 0.050) and the same 110-degree lobe separation angle.

The new heads, cam and intake were run with the same carb, headers and distributor. The only other change was to install a set of 1.7 ratio roller rockers in place of the stock (stamped steel) rockers employed on the stock iron heads. Naturally the pushrods were upgraded as well, from the stock 5/16-inch pushrods used with the stock heads (and guide plates) to 3/8-inch Pro magnum pushrods from Comp cams. After some minor tuning to the carb and a quick timing sweep to determine the best combination, we were rewarded with peak numbers of 527 hp at 5,800 rpm and 533 lb-ft of torque at 4,700 rpm. Torque production was up significantly with the new combination, as the 454 exceeded 500 lb-ft from 3,200-5,500 rpm.

As expected, there was a slight loss in power below 3,200 rpm, but the extra 125 hp and 27 lb-ft more than made up for the losses below 3,200 rpm. Despite the wilder cam timing, the 454 still managed to produced 420 lb-ft of torque at 2,500 rpm, enough to bark even the biggest baloneys. With over 500 lb-ft from 3,200 rpm to 5,500 rpm, this 454 offers one meaty power band.

No matter how you slice it, adding a set of RHS heads and Comp Xtreme Energy cam to your big block certainly qualifies as "action-packed."

Graphs: Demon 454 Head/Cam Test-Stock/Comp Cam vs RHS/Comp Cam
Any time you add over 100 hp to your motor, you know you've made the right move. Replacing the stock peanut-port iron Chevy heads and mild Comp XE256H cam with a set of aluminum RHS (320cc) heads and XE284H cam resulted in a jump in peak power from 400 hp and 508 lb-ft of torque to 527 hp and 533 lb-ft of torque.

Adding the RHS 320 aluminum heads and larger Xtreme Energy cam improved the power output by 127 hp and 25 lb-ft of torque. Had we continued to rev the motor equipped with the stock heads to 6,000 rpm, the difference would have easily exceeded 150 hp. Note that the gains in peak power were not without a minor trade off in low-speed power, as the stock-headed motor offered more torque up to 3,300 rpm.

Airflow Data
STOCK PEANUT PORT VS RHS 320 AS-CAST ALUMINUM
IN/EX IN/EX FLOW GAINS-CFM
LIFT PEANUT RHS 320 IN/EX
0.100 54/45 75/62 +21/+17
0.200 124/102 166/110 +42/+8
0.300 185/118 246/160 +61/+42
0.400 216/141 309/195 +93/+54
0.500 235/157 340/229 +115/+72
0.600 236/168 360/248 +124/+80
0.700 235/174 375/265 +140/+91
SOURCES
Comp Cams
3406 Democrat Road
Memphis
TN  38118
800-999-0853
www.compcams.com
Holley/Hooker
1801 Russellville Road
Bowling Green
KY  42101
270-782-2900
www.holley.com
Demon Engines
Sante Fe Springs
CA
562-694-2559
www.demonengines.com
Pro Comp Electronics
605 S Milliken Avenue
Unit A
Ontario
CA  91761
909-605-1123
www.procompelectronics.com
RHS
3416 Democrat Road
Memphis
TN  38118
877-776-4323
www.racingheadservice.com
By Richard Holdener
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