1968 Plymouth Valiant 427 Engine Swap - Project 7.0: Engine Completion And Dyno Testing

The rest of the valvetrain consists of Comp’s solid roller lifters, Smith Brothers pushrods, and Comp’s beehive valvesprings. We have been using the beehive valvesprings on virtually every engine that we build with excellent results. The springs we selected have a short enough installed height to fit the Edelbrock heads, but they still have enough pressure to work with the solid-roller lifters. We test fitted three different rocker arm designs before deciding to go with the 1.50 ratio units from Comp Cams.

Induction

The Valiant that the engine is going into uses a flat hood with no scoop so our options were limited in terms of intakes that will fit. The 360 engine previously in the car had used a Performer RPM Airgap intake, but with the larger 427 engine we felt it was time to move to a single plane. Of the several choices available, we felt the Victor 340 would best fit the needs of this motor. The plenum and runners in the Victor 340 are a little on the small side for a 427-inch engine, so we sent the intake to the small-block experts at Shady Dell Speed Shop. Ryan at SDSS hand ported our intake and performed some blending work in the plenum area.

Our carburetor choice of a 650 Double Pumper might seem a little small to people used to big drag racing engines, but this engine is going into a track car with 2.94 rear end gears. The NASCAR guys make a lot of power with a 750 main body, so using a 650 main body on our engine didn’t seem out of line to us. We went to Bo Laws (BLP) because they are one of the premier carb builders in the country with expertise in the area of circle track and road racing. BLP built us one of their Weekend Warrior carbs with special road race floats and fully adjustable billet metering plates.

Dyno Testing

We were able to get the engine onto the dyno at Gray’s Automotive for a few pulls before installing it in the car. We always prefer to dyno test an engine whenever possible just to get a baseline on the tune-up as well as to see what the power band looks like. Our headers, oil pan, and water pump were different for the dyno testing than what we ended up using in the car, but the power differences should be minor. We were able to make a number of dyno pulls during our session and only had to make some minor adjustments to jetting and to the ignition. The MSD E-Curve distributor is great to work with on the dyno as it allows us to change the ignition curve by turning a dial. We started off with the distributor locked with 35 degrees of advance, and then tried a few different curves to see how the engine responded. The BLP carb was dialed in very well right out of the box so all we needed was one jet change to get the A/F ratio where we wanted it. Our best pull of the day showed 519 horsepower at 5,800 rpm and 506 lb/ft of torque at 4,100 rpm. We were looking for a 500/500 engine and we exceeded that goal with a little to spare.

Throughout the project we’ve been using the third generation Viper as a benchmark. Those Viper engines were 505 cubic inches and they were rated at 500 horsepower at 5,600 rpm and 525 lb/ft at 4,200 rpm. Given that, the power output of this 427 is right in line with the published Viper numbers. Published numbers don’t always line up with reality, so we are planning to get the Valiant onto a chassis dyno with a Viper in the near future so we can compare the two cars on the same dyno. This Valiant weighs 3,150 pounds ready to race, which is about 200 pounds lighter than a third-gen Viper, so the power to weight ratio is going to slightly favor the Valiant.