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Hi RPM Edelbrock BBC Top End

There is no better way to add power to your big-block than with the right heads, cam, and intake.

Words and Photos By Richard Holdener

What can we say, we love the wrecking yards. Where else can you get a running motor with all the trimmings for less than $300? Okay, our 454 cost closer to $500, but that is just because some idiot journalist keeps writing articles about how cool it is to hop up big-blocks from the wrecking yard. In reality, you don’t have to be junkyard dog to take advantage of what the Edelbrock (and COMP) components had to offer; all you have to do is be a big-block Chevy owner or enthusiast (that’s a big list). You see, a top-end upgrade works for just about every big-block ever produced. We’d think twice about performing the upgrade on a numbers-matching LS6 or L88, but you get the idea. For any of the more pedestrian (or modern) big-blocks, there is plenty of power to be had by replacing the factory induction and cam profile. So, whether installed in a truck, Chevelle, or still languishing in the yard ready to be pulled, a big-block is always a good starting point with plenty of potential.

 


   A top-end kit works well on any big-block, but ours started out life as a Gen VI 454 from a local Pic Your Part. If you plan on replacing the top-end components, you might as well just purchase the short block, but we stepped up to the whole enchilada.

 

The Gen VI 7.4L motors featured large oval-port heads with small (102cc) combustion chambers to help improve compression.

To illustrate just how easy it is to add power to a typical big-block, we decided to get one of our own then subject it to the rigors of the dyno. The two most prevalent big-blocks offered in our LKQ Pic Your Part were the Gen V and Gen VI 7.4L 454s. Though both generations of the 454 shared fuel injection, the differences between the two were significant. The later Gen VI offered increased performance thanks to revised cylinder heads, compression, and camshaft. The EFI induction system offered by the two also differed, but we replaced these with carburetion, so the gains offered by the multi-port EFI over the earlier throttle body injection were nullified. The Gen VI featured a factory hydraulic roller cam (flat-tappet for the Gen V), as well as revised cylinder heads that upgraded from the peanut ports on the Gen V to standard (large) oval ports on the Gen VI. The Gen VI heads also featured small combustion chambers to further improve the static compression ratio. The difference in the cylinder heads would also be moot if you planned on upgrading to the Edelbrock components, but know the dished pistons in the Gen V will still result in a slightly lower static compression.

 


For our baseline test, we replaced the factory fuel injection with a dual-plane, Eliminator intake from Speedmaster.


The intake was combined with a Holley 650 XP carburetor.

Regardless of whether you start with a Mark 4, Gen V, or Gen VI, the Edelbrock components will be a serious upgrade. Just make sure when you say Hi to the RPM heads, you choose the proper components, as Edelbrock offers their top-end upgrades for both flat-tappet and hydraulic roller cams. They even offer a set of RPM, oval-port heads with small (102cc) chambers to maximize the static compression on these low-compression, flat-top piston, factory big-blocks. We chose 110cc versions for our build up, as we plan on upgrading the short block in the near future to either 496 or (at least) 468 status, with forged (domed) pistons to both increase compression and allow for wilder cam timing.

 

   

The factory EFI distributor was replaced by an MSD billet unit, but an HEI will work equally well at this power level.


 

Run on the dyno with the stock heads and cam, the 454 produced peak numbers of 369 hp at 4,700 rpm and 476 lb-ft of torque at 3,400 rpm.

 

 Looking for more power, we decided to replace the factory iron heads with a set of aluminum RPM heads from Edelbrock. The RPM 454-O heads featured a valve spring package designed for use with our hydraulic roller cam and dedicated guide plates.

  Despite the low compression, the factory flat-top pistons in the Gen VI were actually the limiting factor in terms of power production, as they greatly reduced available piston-to-valve clearance. The available clearance was further reduced with the introduction of the larger valves in the Edelbrock heads, as the factory valve reliefs were designed for the stock cam duration and valve sizing. In the end, we were forced to run a milder cam grind than originally supplied by Edelbrock with their package, but fear not, as the aluminum-head upgrade was still plenty powerful.


 


The Edelbrock 454-O heads featured unique roval (rectangular-oval) port openings designed to maximize flow while minimizing port volume. The result was an oval-port head that offered rectangular-port flow and power potential. The flow rate of the intake port (over 300 cfm) suggested the Edelbrock heads will support more than 600 hp on the right application.




 The 110cc, as-cast exhaust ports flowed equally well, offering nearly 220 cfm.


   The 454-O heads were supplied with 110cc combustion chambers that featured a 2.19/1.88 stainless valve package. Edelbrock also offered a high-compression version of the RPM heads with 102cc chambers that would be even better for this flat-top 454.


 Looking for more power, we decided to replace the factory iron heads with a set of aluminum RPM heads from Edelbrock. The RPM 454-O heads featured a valve spring package designed for use with our hydraulic roller cam and dedicated guide plates.

Before applying the Edelbrock, heads, intake, and COMP Cams hydraulic roller cam, we needed to run the 454 in stock trim. The term stock had a slightly different meaning here, as the Gen VI originally came with electronic fuel injection. Naturally, we ditched that stuff in favor of a more user-friendly, carbureted induction system (including computer-controlled distributor). It was also necessary to replace the factory damper, as the high-mileage unit was in pretty sad shape and looked ready to spin the outer hub at any minute. It was replaced by a new unit from Speedmaster. For the baseline test, the Gen VI retained the factory heads, cam, and basic short block, but was augmented with a dual-plane, Eliminator intake, Holley 650 XP carb, and MSD distributor. It turned out the factory Gen VI heads worked best with very little total timing, compared to conventional big-block Chevy heads.

 




   Naturally, the RPM heads were combined with a dual-plane, Performer RPM Air Gap intake to maximize power production through the usable rev range.



 Edelbrock also supplied the necessary gasket kit to facilitate installation of their top-end components.


Due to insufficient piton-to-valve clearance, we were unable to use the cam supplied by Edelbrock for the top-end kit. Instead, we install a COMP XR271HR12 grind that offered a .591/.610 lift split, a 224/230-degree duration split, and 112-degree lsa.

  After dialing in the timing and air/fuel, the carbureted 454 produced 369 hp at 4,700 rpm and 476 lb-ft of torque at 3,400 rpm. That the power peaks occurred at such low engine speeds is a sure indication GM designed that 7.4L for the torque production necessary for heavy hauling.

After the baseline, it was time for the upgrades. Off came the stock heads and intake, followed by removal of the stock hydraulic roller cam. We retained the factory lifters, but the stock stick was replaced by a much healthier COMP grind. The XR271HR12 grind offered a .591/.610 lift split, a 224/230-degree duration split, and 112-degree lsa. Available piston-to-valve clearance allowed a slightly wilder grind (we’ve successfully run COMP cams with as much as 230 degrees of intake duration), but we liked the combination of drivability and performance offered by the 271 cam. We configured the 454 as we would a daily driver, rather than a street/strip combo (but that combo will come). The cam was run with the factory lifters and timing chain, but the augmented short block was definitely in need of some new headgear.

To satisfy the newfound airflow needs of the deep-breathing, COMP-cammed 454, we installed a set of Edelbrock Performer RPM 454-O cylinder heads. Right off the bat, we loved the fact the head were made of aluminum. The weight savings alone was worth the effort, but when you toss in the extra power, swapping heads should be considered almost mandatory. The RPM 454-O heads featured 290cc intake ports, 110cc exhaust ports and 110cc combustion chambers. They also offered a 2.19/1.88 stainless-steel valve package, stock exhaust port locations, and enough airflow to support more than 600 hp on the right application. Our junkyard dog had neither the compression nor cam timing to tax the flow rate of these heads, but we liked the fact they provided plenty of growth potential for future build ups. The 454-O heads were teamed with oval-port version of the famous Performer RPM Air gap intake. The dual-plane design offered the very best combination of peak and average power production for our street-oriented 454.

 

After installation of the Edelbrock heads, intake, and COMP cam, the power output of the 454 jumped to 481 hp at 5,500 rpm and 527 lb-ft of torque at 3,800 rpm. Even better was the fact the Edelbrock heads and intake will support much more power if we decided to upgrade the short block in the future.

After everything was in place and ready to rock, including new (hardened) pushrods and roller rockers, we were able to dial in the new combination. One of our concerns was sufficient spring pressure to work with the revised cam timing. Though the spring specs confirmed sufficient clearance for our sub-.600 lift cam, we were more concerned about rpm potential without valve float. Our fears were soon put to rest as the Edelbrock-enhanced 454 thumped out peak numbers of 481 hp at 5,500 rpm and 527 lb-ft of torque at 3,800 rpm. The new components shifted the torque peak by just 400 rpm, but shifted the power peak by a solid 800 rpm. Torque production now exceeded 500 lb-ft from below 3,000 rpm to 4,800 rpm, meaning there will be no need to hunt for grunt.

 


 

Gen VI 454-Stock vs Edelberock Upgrade

Fresh from a local LKQ Pic Your Part, the Gen VI 454 was somewhat less than fresh, but still managed to produce some stout power numbers. Run first with a Speedmaster dual-plane intake, Holley 650 XP carb, and dyno headers, the otherwise stock 454 produced 369 hp at 4,700 rpm and 476 lb-ft of torque at 3,400 rpm. After installation of the Edelbrock Performer RPM BBC heads, COMP Cams XR271HR12 cam, and Performer RPM Air Gap intake, the power output of the 7.4L big-block increased to 481 hp at 5,500 rpm and 527 lb-ft of torque at 3,800 rpm.

Despite the minimal piston-to-valve clearance, the Edelbrock heads and intake combined with the mild COMP cam to improve the power output by more than 90 hp. While extra top-end power is always welcome, the new combo added over 50 lb-ft of torque, and managed to do so through the entire rev range. Torque is why you want a big-block in the first place, and the only thing better than a little torque is a lot of torque. How do you get all this power? Call Edelbrock and say Hi RPM.

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