`The buzz is all about whether those nitrous camshafts are worth the effort. The skeptics in the crowd say the cams are just a marketing ploy and they don't work. Their point is that if you want more power, just add more nitrous--you don't need a different cam. There may be some truth to that since several companies list cams merely with wider lobe-separation angles as "turbo" or "supercharger" cams. It seems to us there is more to a nitrous cam than just that, so we decided to find out.
All About the O
The "O" in "N2O" is oxygen, and that's the oxidizer that nitrous adds when you squeeze the button. Adding more oxygen allows the engine to oxidize more fuel. Burning that additional fuel is what makes the power.
The performance key is the huge torque gain that comes from a given amount of nitrous added to the engine. For example, most nitrous companies using a 0.063-inch nitrous jet for a single-stage system will rate the package at 150 hp at 6,000 rpm. What many enthusiasts don't realize is the major torque gain created by this combination. That same volume of nitrous at 3,500 rpm is worth a stout 225 additional lb-ft of torque. If an engine is capable of making 400 lb-ft, add the squeeze and the twist jumps to 625 lb-ft, which is monstrous torque at that engine speed.
We talked with Comp Cams cam designer Billy Godbold, and his contention was that since nitrous already adds a ton of torque, why not improve the cam to make more horsepower as well? Ironically, the details of that cam design tend to reduce midrange torque, which is generally considered to be a main area of concern for a street engine. So in theory a nitrous cam will trade torque for a better top-end horsepower number. That's what we wanted to test.
We decided to use a Nitrous Pro-Flow plate similar to the one that won our recent test ("Nitrous Plate Shootout," Nov. '05). This 1-inch-tall plate utilizes Pro-Flow's directed nitrous spray bars combined with Pro-Flow's patented burst plates. The plate assembly and solenoids come prewired using quality Weatherpak connectors.
Cams For Nitrous
Most street-oriented performance cam grinds tend to include a significant amount of overlap. This is the period of cam timing when the piston is coming up toward the end of the exhaust stroke, the exhaust valve is closing, and the intake valve is just opening. As overlap increases, it tends to improve midrange and top-end power by starting the intake process sooner. It also tends to hurt power down low but help it on the top end. This overlap is what produces that distinctive choppy idle quality when reversion forces the exhaust and intake charges to mix.
The problem with lots of overlap when using nitrous is that the additional air and fuel is often lost since some of what is pushed into the cylinder immediately exits past the exhaust valve. One way to prevent this situation is to widen the cam's lobe-separation angle, which decreases the amount of overlap.
This Comp Cams graph does a great job of illustrating the concept of valve overlap. Note the triangle area created by the convergence of the exhaust closing point with the intake opening point. This illustration is of a different cam than the one we are running, but the effect of overlap is the same. By widening the lobe-separation angle from 110 degrees on the XE 274H cam to 113 degrees on the nitrous cam, we reduce the overlap and hopefully improve power.
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.
By adding the exhaust closing and intake opening points on these two cams, you can establish overlap at the 0.006-inch checking point. The "overlap" number indicates only one more degree of overlap between these two cams despite the 10 degrees of additional exhaust duration. All of these points tend to increase top-end power. All specs in this chart are at 0.006-inch tappet lift, which is also advertised duration.
274H/286 XE 278/296 BASELINE NITROUS CAM
DIFFERENCE (DEGREES)Intake Opening 31 BTDC 28 BTDC 3
later Intake Closing 63 ABDC 67 ABDC 4 later
Opening 77 BBDC 99 BBDC 22 earlierExhaust Closing 29
ATDC 33 ATDC 4 later
Overlap 60 degrees
61 degrees 1 degreeIntake Centerline 106 degrees 109 degrees
3 degrees retarded
Our test mule was the Ford 466 detailed in the Feb. '06 issue using 9.6:1 compression, Edelbrock Performer RPM aluminum heads and a Performer RPM Air Gap intake, a Holley 750 carb with an HP body, and 2-inch headers. For this test, we installed the XE 274H Comp hydraulic cam and broke it in on the dyno using a can of GM Engine Oil Supplement oil additive to ensure a smooth wear pattern between the cam and lifters. After several pulls to ensure optimized jetting and timing, Jim Grubbs Motorsports' Andy Hairfield ran the engine several more times to establish a normally aspirated baseline. This is when we noticed manifold vacuum of as much as 1.3 inches at peak power, which indicated the carb was undersized for the application. We also were concerned about using a dual-plane intake manifold with the nitrous, so it was at this point that we swapped on an Edelbrock Victor 460 single-plane intake and a Holley 950-cfm Ultra HP carburetor. The motor responded by trading a little torque for about 10 more peak horsepower, and with that we were ready for our nitrous test. These baseline runs also included the Nitrous Pro-Flow 34-inch nitrous plate under the carburetor.
For the nitrous testing, we chose to run a Nitrous Pro-Flow system similar to the plate system used in our nitrous-plate test a few issues back. In order to test the theory of a nitrous cam, we decided to hit our big Ford with a 175hp shot of nitrous. Nitrous Pro-Flow recommends a 73 nitrous jet combined with a 73 fuel jet with 7.5 psi of fuel pressure for this combination. Pro-Flow also recommends pulling 3 degrees of timing per 50 hp, so we backed the original total from 35 degrees down to 25 to be safe. With this tune-up in place, our procedure was to start the test at 3,000 rpm, hit the nitrous at 3,500 rpm, and then pull it through to 6,000 rpm. Two pulls would be performed with a full bottle at 950 psi to generate back-to-back runs. After a few tries, we realized it was hard for the dyno to harness the massive torque created by the nitrous along with the twist the 466 was already making. So we changed our procedure to loading the engine, hitting the nitrous, and then capturing data from 4,000 rpm and up.
This is the Holley 950HP Ultra carb eith its billit metering blocks and billit baseplate.
Once we had tested the baseline Comp XE 274H cam, JGM's dyno operator Andy Hairfield helpe
On the normally aspirated cam the Ford performed well, cranking out 532 lb-ft of torque at 4,200 rpm combined with a solid 502 hp at 5,600 rpm. Then we pulled back the timing 10 degrees and hit the nitrous. The big Ford literally jumped when we pressed the button, with peak torque rocketing up to a stunning 791 lb-ft at 4,000 rpm. Horsepower numbers also cranked to slightly more than the predicted 175hp gain to a killer peak horsepower of 670. What's interesting is the massive torque this engine cranked out at 4,400 rpm with a gain of 238 lb-ft of torque and 200 hp over the normally aspirated levels.
We swapped in the nitrous cam along with a new set of lifters, broke them in, and then re-baselined the new package to ensure it had the best timing and jetting combination. The first thing we noticed was that the midrange torque fell off, losing over 20 lb-ft of twist below 4,000 rpm compared to the normally aspirated numbers from the first cam combo. As we've explained, this was expected and due mainly to the nitrous cam's longer exhaust profile that opened the exhaust valve earlier. This tends to shift the torque curve higher up the rpm band, which sacrifices torque in the midrange.
On the nitrous cam, the big 466 lost torque with a peak of 529 lb-ft at 4,400 rpm, while the horsepower peak gained slightly with a best of 508 at 5,400. Under the category of compromises, this would certainly hurt normally aspirated acceleration. Now it was time to see what the big Ford would do on nitrous with the nitrous cam in place.
We loaded up a fresh Nitrous Pro-Flow bottle for our squeeze play, hit the button, and watched the power readout jump. Even with the early-opening exhaust lobe the torque spiked again under pressure, but when compared with the normally aspirated cam test, the overall power was down. As expected, we did see the nitrous power improve after the horsepower peak, but the gain wasn't worth the overall power loss.
Test 1: First normally aspirated baseline run with the Comp Cams XE 274H cam, Edelbrock Victor 460 single-plane intake, Holley 950-cfm HP Ultra carb, and 2-inch headers.
Test 2: Second baseline normally aspirated test with the Comp Cams nitrous camshaft. All other components remained the same.
Test 3: Nitrous Pro-Flow 175hp nitrous shot with the XE 274H camshaft. All other components remained the same as in Tests 1 and 2.
Test 4: Nitrous Pro-Flow 175hp nitrous shot with the Comp Cams nitrous camshaft.
The big single-plane intake also required an increase in jetting on the Holley to adequate
We also swapped to a set of Autolite race plugs with cut-back electrodes for all the dyno
This is what a happy nitrous plug looks like after an afternoon's worth of thrashing. The
To keep the nitrous pressure up, we used this simple electric space heater directed at the
All tests were performed on JGM's SuperFlow 901 dyno with the standard correction factor and a 300-rpm/second acceleration rate.
RPM TEST 1 TEST 2
TEST 3 TEST 4 GAIN (3 VS. 1) TQ HP
TQ HP TQ HP TQ HP TQ HP
488 279 - - - - - -3,200
479 292 456 278 - - - -3,400
464 300 420 272 - - - -3,600
463 317 429 294 - - - -3,800
491 355 471 340 - - - -4,000
530 403 517 394 791* 602 - -4,200
532* 425 521 417 789 631 - -4,400
531 445 529* 443 769 645 756* 633 238 2004
,600 525 460 516 452 744 652 728 638
219 1924,800 527 482 523 478 723 660
718 656 196 1785,000 501 477 514 490
700 666 701 668 199 1895,200 506 501
503 498 676 670* 675 668 170 1695,400
485 499 494 508* 643 661 651 669* 158 1625
,600 470 502* 464 494 615 656 623 664
Avg. 500 419 489 412 695 658
What We Learned
Based on the changes in the cam timing between the normally aspirated cam and the nitrous cam, we weren't surprised when the engine lost midrange torque. Unfortunately the only place it gained additional horsepower was after peak horsepower. Still, this was supposed to be a trade-off for the nitrous. Under the nitrous, the nitrous cam should have delivered significantly more horsepower, but in this test we didn't see it. The average power numbers at the bottom of the chart tell the whole story.
As you can see from the dyno results, the nitrous cam never really paid off with more horsepower. Overall, for this particular combination, the nitrous cam perhaps offered too much exhaust duration to take maximum advantage of the nitrous, especially considering all this power was created below 5,500 rpm. For engine combinations that achieve peak power at higher engine speeds, this concept might work better. You can see an indication of this with the increased power at 5,600 rpm with the nitrous cam in the nitrous application. If we had to make a blanket statement from this test, it would be that too much exhaust-event duration will kill power even with nitrous on an engine with a weak exhaust port. So it comes down to, as always, optimizing the combination for your particular engine. It's also possible that this nitrous cam would begin to shine when used with a larger shot of nitrous, such as 250 hp or above, as opposed to our 175hp shot.
We modified this well-used -3 to -4 AN adapter to slip our fuel jet into the line and dyna
JGM's dyno electric-fuel-pump delivery system was set up like many in-car systems as a partial dead-head. This means the two separate Holley VoluMax 250 fuel pumps deliver fuel pressure to a pair of separate regulators before the pressure goes to the engine.
The first pump was targeted to the engine, while the second was used solely for the nitrous. We call this a partial dead-head system because the Holley pumps have circuits that bypass fuel back to the inlet side of the pump under low fuel demand. On the engine side of things, this works OK since when the engine is running a certain amount of fuel is being used, although a certain amount of fuel-pressure creep is generally noted. This makes the fuel pressure read high at idle.
On the nitrous side, things are a little different. Setting fuel pressure with the system dead heading against the fuel solenoid is not accurate because once the nitrous is engaged and the fuel solenoid opens, a given amount of fuel flow will cause the pressure to drop. The only way to accurately set fuel pressure on the nitrous side is to simulate fuel use. To do this, we drilled a -3 to -4 adapter fitting on the -3 side of the adapter until the fuel jet would slip inside the fitting. We then filed down the fitting until it would screw into a length of -3 AN fuel line that was long enough to reach a catch can. Then, with the nitrous fuel pump running and the high-pressure nitrous line unhooked from the nitrous solenoid, we triggered the solenoids and measured the fuel pressure. While the fuel was running, we adjusted the fuel pressure to 6 psi. Before engaging the nitrous solenoid, the static fuel pressure was around 8 psi. This ensured that our nitrous fuel pressure was accurate through both nitrous tests.
`SOURCESComp Cams; Memphis, TN; 800/999-0853; compcams.comJim Grubbs
Motorsports (JGM); Valencia, CA; 661/257-0101Nitrous Pro-Flow; Ft.
Lauderdale, FL; 954/771-6216; wilsonmanifolds.com Summit Racing Equipment;
Akron, OH; 800/230-3030; summitracing.com