350/350 Combo Install - An Old-School Classic

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From the September, 2011 issue of Classic Trucks / By John Gilbert

In the world of hot-rodding old trucks and cars there has always been engine and transmission combinations that have fallen in and out of popularity. At the top of the combo list that’s held the reign the longest and found its way into the greatest variety of recipients is the Chevy small-block 350 coupled with a TH350 automatic transmission. There’s a good reason everything from pre-war Ford cars to tri-five Ford trucks, and anything else along the way ended up with a 350/350 combo—they produced plentiful, reliable horsepower, and did it for low bucks. In 2011 the pendulum has swung back the other way, so now it’s unfashionable to have a 350/350 under the hood unless it’s a vehicle that came that way.

In the case of my ’73 Cheyenne Super I think might have offended the current popular trend by swapping out its original big-block 454 and TH400 for a 350/350 combo similar to stock ’73-87 350/350 offerings. In place of the approximately 720-pound 454 I opted for Year One’s Power Crate 350 that comes in around 175-pounds lighter, and sells for under $3,000. It’s based on a ’96-00 5.7L Vortec with a four-bolt crank, it’s then blueprinted to deliver over 400 horsepower and 400 lb-ft of torque. All Year One Power Crate 350s come with a dyno sheet. The sheet for my engine stated it produced 411 horsepower at the flywheel.

Year One obtains its healthy power increase by custom porting the Vortec heads and using stainless steel 2.02 intake valves and 1.60 exhaust valves, and heavy-duty valvesprings. Its 0.520-inch-lift hydraulic roller cam works in conjunction with 1.6:1 rocker arms to rev the engine up to a 6,000-rpm redline, yet idles down to 800 rpm where it produces 12 hg of vacuum. This level of vacuum is enough to operate original equipment ’73-87 C10 power brake boosters. Recommended fuel for the engine’s 9.5:1 compression ratio is 92-octane. As part of the package, Year One includes a dual-plane aluminum intake manifold that will accept either a four-barrel carburetor or aftermarket fuel injection. Times eight the Power Crate’s 4.030x3.48-inch over-square bore and stroke equation works out to 355 cubic inches of displacement.

I looked to the folks at Gearstar Performance Transmissions in Akron, Ohio, for the TH350 I planned to mate to the Power Crate 350. It was a decision based on past experiences where I have learned many times over that Gearstar transmissions are bulletproof to the point of withstanding extreme abuse beyond the transmission’s rating. You see, Gearstar rates its custom-built transmissions in levels starting at Level 2. A Level 2 TH350 package ($1,295) is rated to withstand 400 horsepower with up to 400 lb-ft of torque. After the TH350 is run on Gearstar’s dyno it’s shipped full of premium ATF, and ready to plug in with all accessories included. In this day and age, although over 25 million TH350s were produced over its production life, good cores are hard to come by. Gearstar’s Zack Farah said they have to sort through five cores to find one good usable core. The TH350 core I shipped to Gearstar for a custom build was pulled from my ’79 Big 10 with only 75,000 miles on it when I upgraded the ’79 to a Gearstar 4L60E. Had the core proven to be unusable there would have been a $100 core charge added to the bill.

Each and every Gearstar transmission built is calibrated to the customer’s truck. The process is to speak with a builder and specify how the truck will be used, including the rearend gear ratio and the height of the tires. The switch from the ’73’s TH400 to the TH350 saves 15 pounds of weight, bringing the 350/350 combo in at almost 200 pounds less than the truck’s original 454/400 powertrain. On a side note, I bought the ’73 minus its original 454/400 drivetrain. In fact, the truck was missing its original motor mounts and transmission crossmember so I had to figure out what needed to be in place before the 350/350 could be installed. All in all, my 400-plus horsepower 350/350 combo came in for well under $5,000, and that’s not a bad deal in anyone’s book. CT



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