Cams and Nitrous. Read if you care :)

**juiced99ws6** · 12-27-2006, 04:13 PM

Nitrous Oxide Cam Shafts

Choosing a Camshaft
Optimum cam timing for a nitrous motor will be different than optimum timing for that same motor off the bottle, so you will have to make a choice as to whether you want the most power with or without nitrous. Obviously if you are driving the car on the street most of the time, you will want the best power off the bottle. If you find that you can spare some power to make your car faster at the track, picking a camshaft to favor nitrous can make a substantial difference when nitrous is in use. If course it is a trade off, but usually the power that you make on the bottle, will be far greater than the amount lost off the bottle.

Pumping Losses
Nitrous oxide adds oxygen, much of which is in liquid form. So you can see that a large intake valve and port is not required or desirable. Larger intake ports cause more of the nitrous to turn to a gas and reduce the amount of normally aspirated power, if the nitrous takes up more room, there will be less room for air, reducing volumetric efficiency. Also, you do not want or need long intake duration or a very high lift, so the intake side of the cam does not need to be any different when nitrous is used. The exhaust is a totally different story. All that extra oxygen and fuel makes for a substantial increase in exhaust. How can the exhaust valves deal with this? It can't, pumping losses go out of sight. Much of the extra power made in the cylinders never makes it to the flywheel, because it is used to push out the exhaust. Since making the exhaust valve large enough and the port flow enough is impractical with most cylinder heads, we must take other actions to cut pumping losses (which is actually just a band aid fix).

Reducing Pumping Losses
The first obvious step is to use a dual pattern cam with longer exhaust duration. Opening the valve earlier will help by getting the valve open more and bleeding off some pressure before the piston starts moving up the bore. This does eat into the power stroke, but more power is freed up than would be made by holding it closed longer (the best solution would be a larger valve and better port). The blow down phase (overlap period) becomes very important in a nitrous engine, because the gasses has much greater velocity and can over scavenge, closing the valve exhaust valve a little earlier helps. Anytime you make more power by reducing pumping losses, you are freeing up horsepower that already existed in the cylinders. The engine will still experience the same loads, but more power will be put to the flywheel and less will be used to push out exhaust.

Camshaft Specs
As I said earlier, the intake needs to remain pretty much the same, but the exhaust needs more duration, an earlier opening point and an earlier closing point. To make this happen, you need to use a dual pattern cam with more exhaust timing, and a wider lobe separation angle. Cam's with 112-116° lobe separations are common is nitrous motors. To keep the intake timing the same, you must install the cam advanced, usually 6-8° advanced. The good things about this are that advancing a cam will bring more low-end (at a trade off of top-end) when running without the nitrous and the wider lobe center angle will also help idle and vacuum. Even the most radical nitrous profiles are usually pretty tame on the street. Ultra high lift cams are not need to make power with nitrous. On the exhaust side, the low lift flow is the most important thing, and must be dealt with much more seriously than high lift flow.