Here’s a Mopar small-block build that pays tribute the original character of the ’67 Plymouth Barracuda Formula S in which it will eventually be installed, while also pumping out more power than the optional 426 Hemi would have given this classic ride.
“We’re looking to build a pump-gas street engine with a nice musclecar burble at idle and in the 425 to 475 horsepower range. I also need 14 to 16 inches vacuum,” explains Bob Gough, noting that power brakes will be included in the restoration. “I’m looking for a docile driver with plenty of grunt when the pedal is mashed.”
Classic idle personality with a strong, flat torque curve. – Robert Lou, Howard’s Cams
“I may have to consider moving the rear springs to accommodate wider tires,” he quipped.
Selecting The Camshaft
The compression ratio was held in check at 10:1, keeping the pump-gas requirement. The key to making the power and moving the torque curve where it could be most beneficial on the street was the hydraulic roller camshaft from Howard Cams.
Howard’s proposed a dual-pattern profile (PN 7108005-09) from its popular Rattler series for the vintage Chrysler LA architecture. Intake duration is 227 at .050 with exhaust coming in at 235 at .050, while the advertised duration is 280/288. Lift at the valve with 1.5:1 rockers is .525 intake, and .5295 exhaust.
“I would expect at least 12 to 14 inches of vacuum or more with a well-sealed motor,” predicts Robert Lou of Howard’s Cams. “This cam is ground on a 109-degree lobe separation. With a recommended six degrees of advance, that will net a 103 intake centerline, a classic idle personality with a strong flat torque curve.”
The Rattler line is designed as a retro-fit bumpstick for classic engines. Its power curve is positioned from 1,800 up to 5,500 rpm, and it offers the stock 1-8-4-3-6-5-7-2 firing order. Gough will be running a Tremec five-speed manual, but owners with automatics are urged to run a torque converter with at least 1,800 rpm stall speed. All cams are ground from American-made cores on dedicated CNC-driven grinders. This particular Rattler is the base line, but more aggressive needs can be met with the Big Mama Rattler and Big Daddy Rattler series that require robust compression ratios and better breathing heads.
“My opinion … this cam is awesome,” praises Gough, adding that he will step up to 1.6:1 rockers to bump the lift up to .560/.565.
Stroking To 416ci
While the cam appeared perfect for the engine and the Barracuda’s street agenda, getting the rest of the valvetrain to install without issues proved quite the challenge. More on that later, but first a look at the engine’s foundation.
A ’67 Cuda, of course, didn’t offer a 340ci, so a block was salvaged from a later model Dodge Dart. Aside from the usual machine work to expand the bore out to 4.070-inch, align the mains and install cam bearings, it needed plenty of work.
“It’s what I call blueprinting the oil system,” says Viau, who runs a deburring tool through the passages to scrape off the casting flaws. “It seems to be fairly pronounced on 340s, more than on big-blocks, and especially the oil passages that feed the heads.”
Notches were also required at bottom of the cylinders to clear the 6.123-inch H-beam rods. Viau says standard replacement rods generally don’t require cylinder notching when going with a Scat 4-inch stroker crankshaft (PN 934020). The cast crank, along with the rods and Wiseco pistons, were balanced along with the flywheel and clutch. Viau was also concerned with clearance between the rods, so he installed chamfered bearings.
On the bottom side, Viau installed a Milodon seven-quart oil pan (PN 30936) and a standard oil pump that he blueprinted. Rounding out the parts list for the short block are Fel-Pro gaskets and ARP Fasteners that were used throughout.
Once the cam and rotating assembly were in place, the assembled Edelbrock Performer RPM cylinder heads (PN 60175) were installed. The only upgrades to the heads were a slight hand-blending of the intake ports and swapping the standard springs for a set from Howard’s Cams rated at 350 pounds open.
Reaching The Goal Of 475 Horsepower
In keeping with the original plans, Viau installed a set of Hughes 1.6:1 aluminum rocker arms to gain extra valve lift. It wasn’t long before a clearance problem was discovered due to the shorter pushrods needed for the hydraulic roller lifters, and the added size of the 1.6:1 rocker arm.
“The 340’s already have a weird angle, and putting a 1.6 rocker just throws it off that much more,” explains Viau, adding that the pushrod holes in the cylinder heads needed enlarging. “I checked them and the clearance was close, but it was right. However, the aluminum heads swelled a little bit when hot and started hitting the pushrods on four cylinders.”
Rather than risk damaging the heads with more grinding, the team opted for a set of standard 1.5:1 rockers to relieve the harsh pushrod angles.
“If I was to make a recommendation to someone, I would tell them not to use a 1.6 rocker with a hydraulic roller,” adds Viau.
The top end was buttoned up with an Edelbrock Air-Gap dual-plane intake manifold (PN 7576) and MSD distributor (PN 8534). After final detailing, the engine was taken to Westech Performance for dyno testing. With the help of shop manager, Steve Brule, and his crew, Viau and Gough tested 750 cfm and 950 cfm carbs. With 36 degrees timing and the bigger carb, the engine pulled 475.8 horsepower at 5,300 rpm, and peak torque of 522.1 lb-ft at 3,500 rpm. Although the power numbers were slightly lower with the smaller carb, that’s the one team decided on for better all-around performance.