Tom Wilson
February 21, 2004
Horse Sense: As is the science in medical journals, dyno reports are notlong on passion. But who wouldn't love standing in the dyno celllistening to 1.3 hp per cubic inch thump out its tune? It almost makesup for the 100-degree temperatures and pizza-only diet.

It's not taking us long to figure out a 347 is the way to go for easy horsepower with a 5.0 engine. Now that we've had our 347 on the dyno for a couple of tests, we're impressed with how easily it churns out the horsepressure. Compared to a stock-bore-and-stroke 5.0, it might as well be cheating! And if you're class racing, it probably is--but that's a different story.

Besides easily made horsepower, a 347's longer stroke means it makes power a little differently. At its most basic, a longer stroke is simply more displacement, and displacement means torque. Furthermore, the longer stroke means the piston is accelerated faster up and down the cylinder for a given rpm, so piston speed is higher in a 347 than in a 302. That produces a stronger vacuum signal at the intake valve, so the incoming column of air is accelerated more forcefully. This has camming and intake manifold consequences, so we thought we'd try a few cams in our 347 mule and find out. Along the way, we were able to also take a quick look at a second intake, flashback to carburetion, and update our rocker studs.

Our three test cams were Comp Cam's largest, most powerful streethydraulic roller bumpsticks. With more than half an inch of lift and 230degrees of duration at 0.050 inch of valve lift, these cams are designedfor hot street and mild strip cars. They'd also do well in open-trackapplications, and we'd be tempted to run the 266 in a slalom engine.

When adding displacement by either boring or stroking, the engine puts a larger demand on the intake and exhaust manifolding. This is no secret, as a larger engine will obviously consume more air than a smaller one, and that air has to pass through the manifolds. Thus, a larger engine can use larger-diameter runners without the airflow becoming "lazy." The same is true for camming. A 347 can tolerate more lift and duration than a 302. Practically speaking, this means a 347 more easily produces vacuum to run the brake booster and smooth the idle. It also means the 347 draws harder through the lift and duration limits set by the camshaft. So, a 347 owner can use a slightly larger camshaft than the 302 owner, yet still retain workable vacuum and idle characteristics.

To put those concepts to the test, we had Westech put our 347 on the dyno and select three of the largest hydraulic roller cams in the Comp Cams catalog, noted in Table One. These are large, power-producing camshafts aimed at serious street and moderate strip engines. They're not going to pass smog and won't win any fuel-mileage contests when putting around town (although they are quite fuel efficient when making power--it's just that they make so much power). What they will do is make great power and torque when combined with other good-breathing parts.

We ordered two of our cams from Comp as cam-only parts, and one cam aspart of a kit. The latter move netted us everything necessary to installand update the valvetrain short of the rocker arms and pushrods. Wealready had roller rocker arms (also from Comp), and the pushrods arefit-to-length units that will vary from engine to engine. Ours workedout to be 8.700 inches long.

Note that all three cams have lobe separation angles of 112 degrees. This is a key measurement when building an electronically fuel-injected engine, as the computer can't handle the erratic vacuum signal produced by a lobe- separation angle greater than 112 degrees. And, because we were running these cams with our standard EEC IV engine management, this was a limit we needed to respect.