Street Engine Build: 416ci Mopar Pulls 475 Horsepower

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

With a goal to deliver plenty of low-end torque, Gough and engine builder Marc Viau of Viau Motorsports knew the stock 273ci engine wouldn’t provide the necessary foundation, but a later-model 340 block could be poked and stroked to 416ci–giving the ‘Cuda big-block power without swapping in a B motor. Along with increasing the displacement via a Scat stroker crank, the team agreed to assemble the engine with Edelbrock heads, Wiseco pistons, Milodon oiling, and MSD ignition. After reviewing parts and estimating the power potential, Gough wondered if he would have enough traction.

“I may have to consider moving the rear springs to accommodate wider tires,” he quipped.

The seasoned 340 block needed considerable work before it was ready for assembly. After cleaning out the oil passages, Viau had to enlarge the oil hole in one cam bearing to ensure proper alignment with the oil feed passage. He also opened up the oil drain holes from the lifter valley to the crankcase, trued up the lifter bores, cleaned all threaded holes, and clearanced the bottom of the cylinders.

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.

The Scat 9000 series cast crank comes with 4-inch stroke, and is designed for 6.123-inch rods. It weighs 54 pounds and features a 2.125 rod pin. Note the internal balancing adjustments.

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 crank was pre-fit to check for clearances.

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.

The Howard’s Cam Rattler camshaft is supported by Howard’s roller lifters, which require significantly shorter pushrods to compensate for the taller body. These Manton pushrods are 5/16-inch diameter.

The double roller timing set gets additional support from a Mopar Performance chain tensioner. The cam was advanced six degress as suggested by Howards.

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.”

Shown here are the dished Wiseco forged aluminum pistons (4.070-inch bore) that provide a 10:1 compression ratio.

Viau adjusts the position of the rings according to manufacturer recommendations before installing the pistons. To ensure proper clearances between the connecting rods, Viau used chamfered bearings, shown next to a stock set. Clearances were double-checked to ensure that the bearings didn’t hang up the rotating assembly.

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.

The Lo-Pro design Milodon oil pan holds seven quarts, features internal baffles, and offers improved ground clearance. Viau blueprinted a standard volume oil pump and retained the stock pressure spring to maintain pressure around 70 to 75 psi. All the gaskets came from Fel-Pro, and the fasteners are from ARP.

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.

Not much work was needed on the 18-degree Edelbrock Performer cylinder heads, other than hand-blending the intake side. The heads come with 65cc combustions chambers, 171cc intake runners and sport 2.02/1.60 stainless-steel valves. Edelbrock says these heads will 251 cfm at .600-inch intake lift and 190 cfm at .600-inch exhaust lift. The standard springs were swapped for a set of beehive springs from Howard’s cams that offer 140 pounds seat pressure and 350 pounds open.

Original plans called for Hughes 1.6:1 aluminum rockers, but problems with the pushrod angle forced a retreat back to 1.5:1 ratio.

This is where the valve train can get hung up: note the tall stature of the roller lifters. Combined with the longer 1.6:1 rockers, the pushrods get very close to the guide holes in the cylinder head. Viau opened up the holes as much as he could and found the minimum clearance, but when the heads heated up and expanded there was contact on four pushrods.

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.

Handling the induction was an Edelbrock RPM Air-Gap dual-plane intake manifold designed for a 1,500 to 6,500 power curve. On the right is the finished long block with timing cover and water pump in place.

“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.

The engine was taken to Westech Performance for dyno testing. Both 950 cfm and 750 cfm carbs were tested with the smaller Holley HP providing the best all-around performance after a number of jet changes. Note the MSD ignition. Final timing was 36 degrees. Dyno headers with 1.75-inch tubes were used for the tests

Article Sources

About the author

Mike Magda

Mike Magda is a veteran automotive writer with credits in publications such as Racecar Engineering, Hot Rod, Engine Technology International, Motor Trend, Automobile, Automotive Testing Technology and Professional Motorsport World.
Read My Articles

Drag Racing in your Inbox.

Build your own custom newsletter with the content you love from Dragzine, directly to your inbox, absolutely FREE!

Free WordPress Themes

We will safeguard your e-mail and only send content you request.

Dragzine - Drag Racing Magazine

We'll send you the most interesting Dragzine articles, news, car features, and videos every week.

Dragzine - Drag Racing Magazine


We will safeguard your e-mail and only send content you request.

Dragzine - Drag Racing Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

Street Muscle Magazine
Hot Rods & Muscle Cars
Diesel Army
Diesel Army
Engine Labs
Engine Tech

Dragzine - Drag Racing Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

  • Streetmuscle Hot Rods & Muscle Cars
  • Diesel Army Diesel Army
  • Engine Labs Engine Tech

Dragzine - Drag Racing Magazine


Thank you for your subscription.

Thank you for your subscription.

Dragzine - Drag Racing Magazine

Thank you for your subscription.

Thank you for your subscription.