A camshaft designed specifically to run with nitrous takes advantage of this wider lobe-separation angle. With nitrous, we've added a bunch of oxygen to the inlet side, much like with a supercharger. As a result, the engine does not need the help of an earlier-opening intake valve (longer duration) to fill the cylinder. The nitrous takes care of that. So we can delay the opening of the intake side using the wider angle, which also reduces overlap.
In addition, nitrous tends to create a very high initial cylinder pressure spike, which means the mixture burns more quickly. Plus, we also have a much greater volume of exhaust gas to expel from the cylinder. Both of these things make it a good idea to begin the exhaust stroke sooner, to ensure we adequately scavenge the cylinder. This minimizes pumping losses once the piston begins its upward movement on the exhaust stroke. The term "pumping losses" describes negative work, or horsepower the engine must use to pump exhaust gas out of the cylinder.
Typically, a normally aspirated street cam will use a 108- to 110-degree lobe-separation angle, while the nitrous cam we've chosen will be ground on a wider 113-degree lobe-separation angle. Keep in mind that our nitrous cam also features a much longer exhaust duration, which also increases the amount of overlap. So by combining a later-closing exhaust lobe with a wider lobe-separation angle, the net effect is close to the same amount of overlap despite the longer exhaust duration. And that's exactly what the Comp Cams nitrous cam delivered.
Since we decided to use our existing Ford 466ci big-block as our nitrous mule motor, we snooped around in the Comp Cams catalog for a Blue Oval big-block nitrous cam, which the company unfortunately does not offer. So instead we used a Comp Xtreme Energy 274H cam (see "Cam Specs" chart) for our baseline. Without a specific nitrous cam for this engine, we worked with Godbold on a custom configuration using a similar existing Xtreme Energy intake lobe. We decided on a 278 advertised intake duration that offers 234 degrees at 0.050 inch. We knew from our first test with the engine ("Easy 500 HP From the Ford 460," Feb. '06) that the exhaust side on this Ford is not particularly strong. The Edelbrock heads are much better than the stock iron castings, but we thought this motor could use some additional help on the exhaust side when hit with nitrous. With that in mind, Godbold suggested a 296 advertised duration with 246 degrees of duration at 0.050-inch tappet lift, which is an additional 12 degrees over the intake side. This additional duration will help scavenge the cylinders, which should help peak horsepower.
To complete the Comp valvetrain, we also used a set of Comp Pro Magnum stainless steel roc
We began the test with this Edelbrock RPM dual-plane and Holley 750 double-pumper. The fir
The first cam for this nitrous cam test is an off-the-shelf Comp Xtreme Energy 274H intended for normally aspirated engines. The nitrous cam is a custom grind spec'd by Comp Cams engineer Billy Godbold. While a custom cam grind might sound exotic, Comp offers this service to anyone, and it takes only an extra day or two and an additional charge as long as you use an existing Comp lobe profile.
DURATION LIFT w/1.77 RR LOBE (ADV.) (@
0.050) (IN.) SEP.Xtreme Energy 274H, In. 274 230
0.562 110 Ex. 286 236
0.565Custom Nitrous 278, In. 278 234 0.576
113 Ex. 296 246 0.589
Comp's custom-grind number on a nitrous cam for a Ford 460 is FF 5446/5209 H113+4.