Mustang MonthlyHow To Engine
Stroker 390 Dyno Test
Trans Am Racing puts our stroker big-block to the test
Last month, we showed you how to take a sedate 390 FE big-block and give it stroke, which ultimately translates into torque and more than its share of horsepower when it's time to pin the butterflies. This time, we want to get into the more finite details on how to build common sense street power into a 390 High Performance V-8. Too many of us get caught up in that dreamy eyed horsepower thing without considering first how our engine will be used.
"Horsepower" is an oft-misused term coined by Madison Avenue advertising agencies because it sells automobiles. It also helps the aftermarket sell engines and performance parts. However, horsepower is a meaningless dynamic unless you are going racing. Even then, it's rather meaningless because horsepower is used only at high rpm and for a short time at wide-open throttle. What matters most is torque--the grunt factor that gets us going before it hands all the fame and glory off to horsepower. We infuse stroke into an engine to make more torque, not horsepower. Torque comes of the raw mechanical advantage of stroke--that long lever you learned about in high school physics. With a lever, you can move the world. The more stroke and connecting rod length (rod ratio) we can give an engine, the more torque we're going to make. And that is what this 442ci FE is all about.
"This 442ci stroker demonstrates how well this combination of parts works together," explains Trans Am Racing's Mark Jeffrey. "When you run the air hat on a dyno, it monitors how much air is being drawn into the engine. The dyno's programming calculates how much power is made. When the percentage of in and out have a huge differential, you know by the VE numbers that you made a poor decision with parts selection. It means your parts aren't working in harmony. To get torque, you need bore, stroke, and the right valve timing events as they relate to piston travel. Although this seems simple in theory, it isn't in reality because there are so many hurdles. You've got to be a great engine architect in order to outfit your FE with the right combination of parts and chase it with proper tuning.
Mark has an instinct for cam and head selection and isn't afraid to push an engine to its limits. In the heart of this 442ci FE stroker is an aggressive, yet streetable, Comp Cams hydraulic roller camshaft, which unleashes power not only from its profile but also from reduced internal friction. It gets better with Comp Cams' new shaft-mounted rocker arm assembly for FE big-blocks with Low-Riser cylinder heads, including the Edelbrock Performer RPM castings that Mark has fitted to this FE. These 1.76:1 ratio, 1.200-inch wide billet rocker arms pivot on precision needle bearings where nothing can disturb their geometry. What's more, they're fully adjustable. End stand kits are purchased separately.
Mustangs Plus set us up with a Milodon oil pan, windage tray, and pick-up for our Trans Am Racing 390/442. Mark needed to do some clearancing in order to clear the crankshaft counterweights and oil pump. The windage tray keeps oil out of the spinning crank and rod journals, which prevents foaming at high rpm. Even if you're building a stock 390 FE, a windage tray is still a good idea for those wide-open throttle experiences. Oil windage also consumes power because it creates internal resistance when oil wraps itself around the crankshaft and connecting rods at high rpm.
When you build an engine, plan an exhaust system to match. Tuning an exhaust system is as tricky as choosing a cam, selecting heads, and deciding on a manifold and carburetor. Your Mustang's exhaust system begins at the header flange and ends at the tailpipes. Every decision you make in between determines rear wheel power.