“It had to run on 87-octane,” says engine builder Terry Walters, when asked about the the 500ci Mopar big-block in this dyno video.

Such a strategy wouldn’t have been on his radar screen only a few years ago as Walters shunned 87 octane fuel with a passion.

“I wouldn’t put it in my lawn mower,” snarls Walters.

Why the change of heart? Turns out a couple of oil company friends told him that much of today’s formulas for 92- and 93-octane may have a tendency to spoil after 30 days. If the fuel isn’t turned over on a timely basis, then customers with performance vehicles may be running on bad gas and not know it. Now 87-octane is discussed with customers looking for street performance.

This engine is going into a ’73 Challenger. The customer had just the block shipped to Walters’ shop in Roanoke, Virginia. From there it was a ground-up build. The cylinders were opened up to a 4.375-inch bore, and a Scat 4.150-inch stroke crank was added. Other bottom-end goodies include ARP hardware and Milodon oil pan with an external pickup. Compression was set at 10.5:1 when the Edelbrock Victor Max Wedge cylinder heads were installed. Not much was done to the heads except for a little work in the bowl area. A Comp Cams hydraulic roller cam with around .600 lift was installed along with Comp 1.6:1 shaft-mounted rockers.

The dyno test shown here was run with an Edelbrock single-plane manifold and Holley 1050 Dominator. Results: 636 horsepower and 672 lb-ft peak torque.

The vehicle owner won’t be able to fit the big manifold and carb under his hood, so an Indy dual-plane intake and 950cfm will offer about 2.25 inches more clearance; however, power is down nearly 30 horsepower.

BTW, Walters is also an accomplished Pro Stock driver who, like many others, has been on his lid after a wild ride. Check it out on his webpage.