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