Building A Budget 347 Engine - How To

How do you make power in a reliable street engine? First, we can tell you there are no free lunches when it comes to making power. If you want whopping amounts of power, expect to sacrifice durability, fuel economy, and cash. If you want durability and fuel economy on the cheap, you're going to give up power. It's all about compromise.

Making power is as fundamental as high school physics-turning thermal expansion into rotary motion. The objective is to huff as much air and fuel into each chamber as is possible during the brief moment of time the intake valves are open followed by squeeze and spark. If you want your 289/302 to operate with the authority of a big-block without the weight penalty, Trans Am Racing and Summit Racing Equipment can help with affordable 347ci small-block engines that offer both durability and good street power.

How do you turn a 289 or 302 into 347ci? You take those 4.030-inch bores and stroke them to 3.400-inches of piston travel. With the increase in displacement comes more fuel and air per charge plus the mechanical advantage of stroke. The longer the connecting rod (rod ratio), the greater your piston dwell time top and bottom, which yields more power all by itself. This means you must shop carefully for small-block Ford stroker kits and learn everything you can about them before laying down the cash. Bore and stroke are your first concerns. Then you must consider piston type and design, rod ratio, stroke, and what you will have to do in the way of block modifications.

Every engine builder has a different approach to engine architecture. All want good numbers from their engines. Some go for all-out horsepower, which doesn't always work on the street unless you like speeding tickets and high gas receipts. Horsepower is an element of speed. Torque is the process of getting up to speed. Torque always hands off to horsepower. If you're building a strong street engine, you need a broad torque curve-an engine that pulls like stink from around 2,500 rpm and keeps hauling to 5,500 rpm when it hands off to peak horsepower around 6,000 rpm.

Mark Jeffrey of Trans Am Racing builds his street engines with uniform amounts of horsepower and torque. He likes an engine you can drive to work with during the week and go racing with on Saturday night. This is what our Budget 347 is all about-torque for the street and horsepower for racing. What's more, it doesn't have to be expensive because we're going with a beefed-up cast-steel crank (a fancy term for nodular iron), strong I-beam connecting rods, and forged flat-top pistons along with low-friction rings. We've also opted for an aggressive roller street/strip cam from Comp Cams. On top are Mark's own port-massaged Edelbrock Performer RPM cylinder heads with Air Gap induction and Holley carburetion. As always, Mark has specified MSD ignition to light the mixture.

Next month, we're going to the dyno lab at Westech Performance to show how much power is made and what tuning changes can be performed to make more of it.

Dynamic Balancing
There's a source of destruction trying to beat its way out of every engine. Vibration, no matter how small, does engine damage. If you can feel vibration at the steering wheel or shifter, imagine how bad it is inside the engine.

Dynamic balancing of rotating and reciprocating parts means smoothness at all rpm ranges. From the factory, engines get a process called Detroit balance, which is mass production-style of balancing. This means getting balance within a rather large window, which isn't good enough for a performance engine. Go the extra mile and have your engine builder dynamic balance your engine's internals.

Dynamic balancing performed by your engine builder will deliver smoothness at all rpm ranges. MCE Engines in Los Angeles, for example, likes to get parts within 1/10 of a gram. Most builders are within 1/2 gram. Regardless, when balancing an engine, the crankshaft is spun like a tire on a balancing machine. Pistons, rings, and rods are weighed for compatibility with crankshaft counterweights to where they doe-see-doe around each other smoothly.