1. home
  2. how to
  3. Bolt On 230+ HP to a Motorhome 454CI Big-Block

Bolt On 230+ HP to a Motorhome 454CI Big-Block

We bolt on Trick Flow top-end kit and find over 230 horsepower hiding in the crusty engine

The RV it came from might have been a junker, but this 454ci big-block wasn’t ready to call it quits.
Evan PerkinsAuthor, Photography

Hot rodding is a hobby—not a career—for the vast majority of us. We drool over billet, but settle for cast, and we pinch pennies to eke the most out of our performance purchases. Horsepower per dollar is worth its weight in gold, and with this 87-octane-compatible, 567-hp barnstormer of a build, welcome to El Dorado.

Welcome to the 1980s. This past-its-prime motorhome is ugly, but who could turn down a free big-block?
There's a right way to pull a big-block from a motorhome. This isn't it. Being that the body was scrap and there was no intention to save it, the quickest way to the prize was through the grille—or where the grille used to reside.

It all started when Car Craft friend Curtis Mowery inherited a 1986 Suncrest Motorhome. The interior was decrepit, and the external fiberglass paneling was cracked and rotting. The engine, however—a 454-cu in. Mark IV big-block Chevy-was healthy and showed only 35,000 miles on the clock. Behind it was a TH400 that had been treated to a recent rebuild. As a whole, the RV was an ungainly eyesore. Under the skin, it was a perfect drivetrain donor.

Although vehicles of this stature aren't the most common—or practical—platforms out there, including Ford, Chevy, and Dodge all offered big-blocks for motorhome service. We have seen several make appearances at junkyards over the years, though they present a much more challenging engine-pull scenario, which we'll attest to firsthand.

Knowing the RV was a lost cause from the get-go, no time was wasted being gentle pulling the engine. Sawzalls buzzed, pry bars levered, and cutting-torch flames licked away obstacles. Soon the grease ball of a big-block was out and headed to Westech for a dyno and some mandatory speed parts. Afterward, it would find a new home between the fenders of a 1962 GMC truck project.

At the Dyno

"Why don't you ever bring me nice things?" wonders Westech's Steve Brul , unamused at the crusty turd in his dyno cell.

Smog-era big-blocks get a bad rap. Their sub-8.0:1 compression rations, tiny cylinder-head ports, and anemic camshaft grinds are the main culprits. But what would the 31-year-old engine crank out on the engine dyno? Although it had a relatively conservative odometer reading of 35,000, lugging around a multi-ton motorhome isn't an easy life.

Troy Goldie loaded the big-block onto the dyno. With the exception of a set of dyno headers, we ran the engine exactly as it was set up in the motorhome. The result was a surprising 335 hp and 485 lb-ft of torque.
The engine had 35,000 hard miles, 31 years, and all the grime to back it up.
For the initial dyno run, we used the original 800-cfm Quadrajet carb. For subsequent tests, we used a Holley due to the tuning parts we had on hand. However, to keep costs down, the Q-Jet could easily be repurposed.

Westech's Troy Goldie buckled the big-block into the dyno cell, and Steve Brul worked the throttle for the first pull. Through the stock Quadrajet carburetor and a set of uncorked dyno headers, the engine delivered an oddly quiet 335 hp and whopping 485 lb-ft of torque. It was definitely healthy and far livelier than expected.

But who can leave well enough alone? The goal wasn't simply to validate a stock RV engine, but to see what kind of grunt was locked inside those 454 cubic inches by installing a better-breathing top end. To accomplish that goal, we turned to Trick Flow Specialties for one of its complete top-end kits (PN: TFS-K413-580-560). The kit included gaskets, valvetrain and camshaft, fasteners, and a set of PowerOval 280 as-cast cylinder heads. The kit bottom-lined at $3,499.97 on Summit Racing. That is certainly a significant amount of coin, but it's feasible for most gearheads with a project-car piggy bank—or during tax return season. The only thing not included in the kit was an intake and carburetor, so we ordered a Professional Products single-plane (PN 53037) from Summit Racing for the price of $209.97. Brul did note that a dual-plane intake would have likely provided more torque down low without giving up much on the top end due to the engine's planned conservative redline.

Trick Flow's top-end kit contained everything needed for the swap. The cam specs are aggressive enough to produce real power, but the engine will still idle in gear and generate enough vacuum to support power brakes.
We disassembled the engine to a short-block in preparation for the new top end. The pistons had plenty of carbon, but looked healthy otherwise.
Brul installed Trick Flow's hydraulic roller cam, timing set, and a thrust button to control camshaft endplay.
Curtis Mowery holds a genuine "RV cam" sourced from the wild. Did you know every Craigslist engine ever has one of these?
With the cam in place and decks cleaned up, Trick Flow's PowerOval 280 heads are installed.
The kit included pushrods, assembled cylinder heads with springs, and 1.7:1 ratio roller rockers.
A Professional Products single-plane manifold was used, but Steve recommends an air-gap-style dual plane for street use, noting they offer significantly more midrange and sacrifice only a few ponies up top. A Holley 950 Ultra HP provided fuel mixture for the final dyno tests.

The old top end was unceremoniously yanked from the virgin motor, revealing carbon-coated but undamaged pistons. We cleaned the deck surfaces and laid fresh Felpro gaskets in place. The Trick Flow heads were installed with included ARP head bolts. This kit utilized a roller cam ground with 236 degrees of intake duration and 242 of exhaust duration as measured at 0.050-inch tappet lift. The lobe-separation angle was cut at 112 degrees and valve lift measured 0.600 inch on the intake and exhaust.

Because this engine was not equipped with a cam-stopper plate (as some later big-blocks are), it was necessary to control camshaft endplay. Brul grabbed a roller thrust bearing from Westech's parts stores and installed the camshaft, timing chain and sprocket, lifters, and the remainder of the valvetrain. The intake was then bolted in place and the factory HEI distributor was reused. We opted to borrow one of Westech's Holley Ultra HP carbs because of the tuning parts on hand, but in theory, the Quadrajet, with its 800-plus cfm, could've been reused.

With the engine buttoned up, it spun the dyno once more, recording 560 hp and 530 lb-ft of torque—a 225 hp improvement over stock! Is a head and cam swap a bolt-on affair? We'll gladly stand on our soapbox and say yes! On a pushrod engine, the job can easily be accomplished in a day, requiring no specialized tools and with no need to pull the engine from the car—sounds like a bolt-on to us. Thrilled to have bolted 200-plus horsepower onto an otherwise-stock RV engine, we began to ponder where else power was hidden. After some quick math, it was determined the engine only had an 8.2:1 compression ratio—as pump-gas friendly as compression ratios come. So to verify the affliction for cheap gas, we purged the dyno tank, refilling it with run-of-the-mill 87-octane from a local station. If detonation were to occur, the dyno would show a reduction in power and torque. Instead, it showed a 7-hp increase and 5-lb-ft rise in torque. This was a legitimate pump-gas big-block—for a total of $3,709.94. Next time you're perusing the local boneyard, give that monstrous motorhome a second look.

The last pull of the day was conducted on lousy, California-standard 87-octane fuel. Despite the swill, the engine cranked out an awesome, 567.2 hp and 537 lb-ft of torque, sounding like a real big-block in the process. The total horsepower improvement for the day was a whopping 232.2 hp. Not bad for a day's work.

Sources

Holley; 1.866/464.655; Holley.com
Professional Products; 323/306-5067; Professional-Products.com
Summit Racing; 800/230-3030; SummitRacing.com
Trick Flow Specialties; 888/841-6556; TrickFlow.com
Westech Performance; 951/685-4767; WestechPerformance.com