Stepping Up: Build vs Rebuild

Words And Photos: Richard Holdener

Some builds come out of necessity, like when you blow up your motor trying to add too much nitrous. But some just plain make sense, or maybe more accurately, cents! The build of this 496 fit into the latter category, as our junkyard 454 was still in perfect running condition. As happens, a few limitations got us thinking about making some changes, then (as always) one thing lead to another, and pretty soon we had a full-fledged rebuild on our hands.

Our story began in a local LKQ Pic-a-Part, where we managed to secure a 1998 Gen VI 454 Chevy. The 7.4L offered plenty of positive attributes, including a factory hydraulic roller cam, increased compression (over the previous Gen V motors), and improved cylinder heads featuring the large oval ports (Gen V featured less-desirable peanut ports). After replacing the EFI induction with an Edelbrock Performer RPM intake, Holley carb, and MSD distributor, the 454 truck motor produced 367 hp and 476 lb-ft of torque. The junkyard Rat was hitting on all eight, but was in desperate need of more power.

Knowing the big-block would respond to more aggressive cam timing, we swapped out the factory truck cam in favor of an Xtreme Energy grind from COMP Cams. To add as much power as possible, we installed a COMP XR282HR hydraulic roller cam. The COMP cam offered a .510/.520 lift split, a 230/236-degree duration split, and 110-degree lsa.

The cam swap also required a valve spring upgrade. To provide for the lift and rpm potential of the new cam, we installed a set of 26120 beehive springs from COMP Cams. The springs were teamed with new retainers and rotator eliminators, both from COMP Cams.

Our cam choice was based on the available piston-to-valve clearance offered by the stock head and piston configuration. Any more duration would push the clearance beyond the safe zone and possibly into contact.

The cam swap did indeed improve power, as the 454 spit out 422 hp and 506 lb-ft of torque. The power gains were welcome, but we couldn’t help but want even more. Though we briefly considered a ZEX nitrous plate and even boost, we eventually decided to continue following the all-motor route (at least for now).

After eliminating power adders, we decided to take a closer look at the 454. The head flow would certainly support additional power, but our cam timing was limited by the available clearance. Obviously a head swap was possible, but without sufficient cam timing to take advantage of the extra air flow, the gains would be minimal. Besides, the stock Gen VI heads featured 102cc combustion chambers and almost any after market head would be closer to 120cc, resulting in a significant drop in static compression.

To facilitate any serious power gains, we would have to address the piston-to-valve clearance, which meant either fly cutting or replacing the factory pistons. Replacing the factory pistons (even without a rod change) would still require complete disassembly and rebalancing the combination. Basically, this meant a complete rebuild with all new rings, bearings, and gaskets. In the end, this would give us a 454 (or slightly larger if we bored the stock block), which could certainly make power. But if we were going to all the trouble to get new pistons, why not step up to even more power with additional displacement?

Big-block builds are all about inches, after all; that’s why we chose a 454 over a 350 small-block in the first place. Along these lines, if a 454 is good, then anything bigger must be even better, right? It is this line of thinking that eventually took us to the stroker experts at SCAT. Though they offer standard and lightweight, billet and forged versions for high-horsepower applications, we went the more affordable route and chose a 9000-series crank.

A step up in strength and quality from a production crank, the SCAT stroker crank was precision ground, micro polished, and featured a 4.25-inch stroke to up the displacement from the standard 4.00-inch factory GM crank. The SCAT crank was teamed with a set of Pro Stock I-beam rods and Mahle .030-over (small-dome) pistons. The dome combined with the 118cc chambers provided not only a hike in static compression over the stock heads, but also the necessary valve clearance. Adding Total Seal rings and Federal Mogul bearings completed the stroker short block.

Instead of a low-compression 454 with inadequate valve clearance, we had a 489 stroker with plenty of clearance. Now, it was time to make power.

The displacement ensured the 489 would be more powerful than the cam-only 454, but we wanted the difference to be substantial. After all, why go to the trouble of building a big motor if it doesn’t make big power?

Recognizing the newfound piston-to-valve clearance, we selected our camshaft accordingly. Since our goal for the build was balanced street/strip performance, we selected a small solid-roller profile from COMP Cams. The 300BR-14 offered .652 lift, a 255/262-degree duration split, and 114-degree lsa. To work in the 1996-99, Gen-VI block, the roller cam was teamed with a set of .300-tall solid-roller lifters and a double-roller timing chain (all from COMP Cams).

Since the cam and timing chain were designed for a Gen 4 block, it was necessary to eliminate the factory cam retaining plate in favor of a traditional cam button. The swap also required the use of a custom front cover (pt#217) from COMP Cams to provide the necessary room for the double-roller chain (factory Gen VI covers must be run with a single-roller chain).

Obviously, the cam wasn’t going to make power on its own, so we combined it with a set of Edelbrock E-CNC 355 heads. The rec-port, aluminum heads featured full CNC porting to maximize flow. Additional features included a 2.30/1.88-inch stainless steel valve package, 145cc exhaust ports, and intake flow rates nearing 370 cfm. These Edelbrock heads had the ability to support more than 750 hp on a wilder (or larger) application, meaning they were more than enough for our street/strip stroker.

The Edelbrock heads were topped with (what else) an Edelbrock, single-plane 454 R intake and Holley 950 XP carburetor. Additional components in the build up included 1.70- ratio roller rockers, hardened pushrods, and solid-roller valve spring upgrade from COMP Cams.

Milodon supplied a complete oiling system that included a street/strip pan, pick up, and windage tray. They also supplied a HV oil pump, HD pump shaft, and necessary main studs for use with the windage tray. On hand to eliminate unwanted vibration was a Speedmaster damper, while ignition chores were handled by a billet MSD distributor.

As much as we like a good junkyard, rat motor, we were even more excited about running the stroker. As always, we treated the new motor to a few break-in cycles before hitting it hard. You will remember our 454 produced 422 hp and more than 500 lb-ft of torque. We are pleased to announce all our hard work paid off, as the stroker not only made more power than the smaller 454, but did so by a significant margin.

After tuning, the 489 produced peak numbers of 722 hp at 6,500 rpm and 627 lb-ft of torque at 5,500 rpm. This stroker motor was now making peak torque higher than the 454 made peak power. The combination of displacement, head flow, and proper cam timing unearthed an extra 300 hp and 120 lb-ft of torque.

Obviously, we made the right decision stepping up to the stroker rather than popping pistons in the 454. Where the cammed 454 made a good truck motor, the 489 made a good motor, period! No matter what your performance plans, a stroker will always offer more power everywhere. With our stroker offering more displacement and power (and a static compression ratio near 10.0:1), we couldn’t help but wonder about stepping up even further with our ZEX plate nitrous system or a Vortech YSI. After all, the only thing better than a 700-hp stroker is one making 1,000 hp, right?

Building the stroker offered a slight increase in power over the 454. Yeah, and by slight we mean HUGE! The 489 stroker offered more peak power, more peak torque, just more of everything. The bigger motor was better in every way, but that should not be surprising given the improvements in displacement, compression, and cam timing, not to mention cylinder head, induction, and exhaust flow. It really isn’t a fair comparison, but the limited available piston-to-valve clearance offered by the Gen VI 454 gave us no choice. Besides, we were excited about combining the E-CNC 355 heads and the COMP blower cam, as we have power adder plans for the stroker after this test.

Sources

ARP
arp-bolts.com

COMP Cams
compcams.com

Edelbrock
edelbrock.com

Holley/Hooker
holley.com

Mahle
us.mahle.com/mahlemotorsports

Milodon
milodon.com

MSD
msdignition.com

Scat
scatenterprises.com

Speedmaster
speedmaster79.com

Total Seal Rings
totalseal.com

About the author

PPN Editor

Power & Performance News is the source for news, tech and products that help you get more performance from your vehicle. If powertrain performance projects and hardcore technical content are your interest, Power & Performance News is the publication designed for you. Our acclaimed editorial staff covers all aspects of engine and driveline upgrades with a mission of presenting information that is both interesting and achievable for the “average car guy”.
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