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Cheap Chevy Upgrade: Low-Compression 454

Making power with Chevy’s workhorse big-block V-8.

"I have a complete running 1973 big-block Chevy truck chassis with all the components. What would be the cheapest and most direct route to wake this engine up? I'm looking more for torque than big horsepower. I know this was the low point on the performance scale, but it was too good of a deal to pass up. It has a TH400 and 4.10:1 rear-end gears. "
—Mark Cash; Vanport Trucking, Vancouver, WA

Marlan Davis replies:

Three key words here: "running," "budget," and "torque." I assume the engine is basically sound, a complete rebuild anytime soon isn't in the cards, and you want to just run what you have with a minimum investment. A 1973 truck 454 was typically factory-rated 240 hp at 4,000 rpm and 355 lb-ft of torque at 2,800 rpm. (These are SAE J1349 net power ratings, a more conservative test standard than SAE J607 typically used to rate traditional muscle car engines and even now still the standard for hot rod and racing engine dyno testing.) Assuming the engine is stock, the key bottleneck is a weak 8.2:1 factory static compression ratio (and that's optimistic; a non-blueprinted motor can be to of a point lower than its official rating). Low-compression engines don't respond well to big hot rod cams, and you want to concentrate on torque, anyway. Instead, wake up this low-compression engine by building some cylinder pressure.

Summit Racing PN SUM-K1300 high-torque RV cam for big-block Chevy.

The cheapest and most direct way to accomplish that is by installing a high-torque RV hydraulic flat-tappet cam. Available from just about everyone, so-called RV cams are designed to maximize low-end performance with wide lobe separation angles and short durations (compared to typical hot rod cams). For instance, Summit Racing's RV cam and lifter kit (PN SUM-K1300) has a 1,000-4,500-rpm powerband. Although duration (at 0.050-inch tappet lift) is within 5 degrees of the stock cam, it has considerably more lift (see table). The Summit package goes for $119.99 (as of Sept. 2019)—talk about budget! At this level, you can even slide by with the stock valvesprings if they're in good shape. Be sure to run a good break-in oil with plenty of zinc (ZDDP) additive. After break-in, run a high-zinc hot rod type oil like Lucas's 20W-50 hotrod blend.

 

Camshaft Specs Compared
Grind Stock 1973 454 truck (VIN L) Summit SUM-K1300
Valve lift (1.7:1 rockers) 0.438 int. / 0.438 exh. 0.475 int. / 0.500 exh
Duration (0.050 tappet-lift) 210 int. / 213 exh. 208 int. / 218 exh.
Lobe centerline 109 int. / 117 exh. 107 int. / 117 exh.
Lobe separation angle 113 112

 

A good power/dollar value for waking up a lazy 454: A low-compression 454 take-out from an RV made 560 hp with a Trick Flow top-end kit, a single-plane intake manifold, and a Holley 950-cfm Ultra HP carb. The kit's hydraulic roller cam specs are aggressive enough to produce real power, but the engine was said to still idle in gear and produce decent vacuum.
Big-tube, full-length, 4-into-1 headers aren't needed with this combo. Stock exhaust manifolds into traditional dual exhaust pipes work fine. If you have the budget for headers, use tri-Y headers for low-end torque. Doug Thorley offers its famous Tri-Ys for just about any popular application. This ceramic-coated set (PN THY-303Y-C) fits 1973-1981 two-wheel-drive Chevy/GMC 454 pickups and related vehicles. Photo: Doug Thorley.
The top-end kit included Trick Flow's PowerOval 280 as-cast aluminum heads. The oval intake port design is designed to produce excellent low and midrange torque while the modern heart-shaped, CNC-profiled combustion chambers yield a quicker, more efficient burn that helps fight preignition and detonation. Photo: Courtesy of Trick Flow.

Do you have more coin to spend? If the bottom end isn't tired and you want to make some serious numbers (albeit with some low-end losses; there's no free lunch), consider a top-end kit built around a hydraulic roller cam and aluminum cylinder heads. Trick Flow Specialties has a complete package with the cam, valvetrain, cylinder heads, ARP fasteners, and gaskets (PN TFS-K413-580-560) that sells for $3,753.92 at Summit (Sept. 2019). Using this package, a 35,000-mile RV take-out low-compression 454 stocker made 560 hp and 530 lb-ft on Westech Performance's engine dyno, a gain of 225 hp and 45 lb-ft over the engine's stock baseline of 335 hp and 485 lb-ft. (These numbers are corrected under the more liberal SAE J607 hot-rod standard test procedure.)

Sources

Doug Thorley Headers; Corona, CA; 800.347.8664; DougThorleyHeaders.com

Holley Performance Products; Bowling Green, KY; 866.464.6553 (tech), or 270.782.2900 (general); Holley.com

Lucas Oil Products Inc. ; Corona, CA; 800.342.2512 or 951.270.0154; LucasOil.com

Summit Racing Equipment; Akron, OH; 800.230.3030 (U.S.) or 330.630.3030 (outside U.S. ); SummitRacing.com

Trick Flow Specialties (TFS); Tallmadge, OH; 888.841.6556 or 330.630.1555; TrickFlow.com