Nitrous cams, a brief tutorial
05-14-2007, 06:08 AM
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Nitrous cams, a brief tutorial
A cam optimized for nitrous (N) is quite different than a cam optimized for NA use. It has the potnetial to make more power while on N, in the most extreme case on the order of 10-15% of the nitrous boost, but lose quite a bit compared to an optimzed NA cam off the juice. I want to take a minute to explain a little about this and offer suggestions about compromises that will work pretty well with either.
Using N poses a problem. An optimum head for nitrous use would have a larger exhaust valve at the expense of a smaller intake valve. When you add N, you are drastically increasing the volume of exhaust gasses needing to be pumped out. If you add a 150hp shot on to a 300hp motor, 50% more exhaust gas is created, for example. Not only due the pumping losses go up dramatically, there is more residual gas and contamination of the intake charge to deal with. The exhaust valve area would need to be 50% larger to fully compensate.
Not only is 50% more exhaust valve area completely impractical, it would severly compromise NA power. So, the cam must be used to compensate. The method of compensation is to open the exhaust valve earlier. As a rule of thumb, the range to look for is 10-20 degrees earlier with 150-300hp of nitrous. There are a couple of ways to open the exhaust earlier. We can increase the LSA, increase the exhaust duration, or advance the cam. As with all aspects of cam design, there are always tradeoffs. Increasing the exhaust duration will also increase overlap when typical cam profiles are used. If we had exhaust lobes specifically designed for nitrous available, which most of us do not, just the opening side could be lengthened. Increasing the LSA opens the exhaust earlier, but decreases overlap. As with a wider exhaust lobe there will be a downside if the overlap was correct in the first place.
This leaves us with advancing the cam. Let's look at some valve events by starting with a typical aggressive SBC HR cam: 294/300 on a 110LSA installed 4 degrees advanced. The valve events are IO/IC-EO/EC 41/73-84/36. This gives us 77 degrees of overlap. We want to use a 100hp shot and compensate by opening the exhaust 10 degrees earlier. The valve events we want are 41/73-94/36. To get this, we can open up the LSA to 112.5, increase the exhaust duration to 310 degrees, and install it on a 106ICL (6.5 degrees advanced). We now have valve events of 41/73-94/36 with 77 degrees of overlap - just what we wanted. This might lose 20hp or so compared to the first cam off the juice, but gain an additonal 20-30hp on it.
The compromise position is somewhere in between. Open up the LSA a couple of degrees, advance the cam a couple, and bump up the exhaust duration a bit. The choice is yours - but keep in mind that most cams are so far from optimized in the first place that a properly chosen nitrous cam is likely to be better both on and off the juice.
Rich
Using N poses a problem. An optimum head for nitrous use would have a larger exhaust valve at the expense of a smaller intake valve. When you add N, you are drastically increasing the volume of exhaust gasses needing to be pumped out. If you add a 150hp shot on to a 300hp motor, 50% more exhaust gas is created, for example. Not only due the pumping losses go up dramatically, there is more residual gas and contamination of the intake charge to deal with. The exhaust valve area would need to be 50% larger to fully compensate.
Not only is 50% more exhaust valve area completely impractical, it would severly compromise NA power. So, the cam must be used to compensate. The method of compensation is to open the exhaust valve earlier. As a rule of thumb, the range to look for is 10-20 degrees earlier with 150-300hp of nitrous. There are a couple of ways to open the exhaust earlier. We can increase the LSA, increase the exhaust duration, or advance the cam. As with all aspects of cam design, there are always tradeoffs. Increasing the exhaust duration will also increase overlap when typical cam profiles are used. If we had exhaust lobes specifically designed for nitrous available, which most of us do not, just the opening side could be lengthened. Increasing the LSA opens the exhaust earlier, but decreases overlap. As with a wider exhaust lobe there will be a downside if the overlap was correct in the first place.
This leaves us with advancing the cam. Let's look at some valve events by starting with a typical aggressive SBC HR cam: 294/300 on a 110LSA installed 4 degrees advanced. The valve events are IO/IC-EO/EC 41/73-84/36. This gives us 77 degrees of overlap. We want to use a 100hp shot and compensate by opening the exhaust 10 degrees earlier. The valve events we want are 41/73-94/36. To get this, we can open up the LSA to 112.5, increase the exhaust duration to 310 degrees, and install it on a 106ICL (6.5 degrees advanced). We now have valve events of 41/73-94/36 with 77 degrees of overlap - just what we wanted. This might lose 20hp or so compared to the first cam off the juice, but gain an additonal 20-30hp on it.
The compromise position is somewhere in between. Open up the LSA a couple of degrees, advance the cam a couple, and bump up the exhaust duration a bit. The choice is yours - but keep in mind that most cams are so far from optimized in the first place that a properly chosen nitrous cam is likely to be better both on and off the juice.
Rich
Last edited by rskrause; 10-14-2007 at 05:28 AM.
05-14-2007, 11:42 AM
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It's good to see an informational and educational post on this subject. Certian other "Cam Gurus" on this and other sites continually preach the opposite and about "inside knowledge" of what works. Never any proof or science to back it up, and nothing tech related.
I have to completely agree with everything you've posted. Setup is key, and compromise is a given. Expect to give up something NA, for big rewards on the bottle. While most of the tech above pertains to larger shots 150+ (as you posted), it is good to keep in mind for those of us who plan on spraying the majority of the time at the track.
As an example of your tutorial above, I'll offer my results as an example. My car is setup for the bottle. Nitrous specific pistons, cam and head porting. The cam has a higher numerical LSA and wider split than a typical NA cam. I have a stall and gearing setup to optomize a large shot. I gain about 9 tenths to 1 second in the 8th and 10mph for every 100hp I spray. I have seen dozens of other cars at the track and on the boards see similar gains from 150 - 200 shots.
Like most nitrous cars, mine isn't breaking records on motor, but it is night and day differnet on the bottle. Slower on motor, faster on the spray.
Build a car with a goal in mind and optomize the setup for that goal.
I have to completely agree with everything you've posted. Setup is key, and compromise is a given. Expect to give up something NA, for big rewards on the bottle. While most of the tech above pertains to larger shots 150+ (as you posted), it is good to keep in mind for those of us who plan on spraying the majority of the time at the track.
As an example of your tutorial above, I'll offer my results as an example. My car is setup for the bottle. Nitrous specific pistons, cam and head porting. The cam has a higher numerical LSA and wider split than a typical NA cam. I have a stall and gearing setup to optomize a large shot. I gain about 9 tenths to 1 second in the 8th and 10mph for every 100hp I spray. I have seen dozens of other cars at the track and on the boards see similar gains from 150 - 200 shots.
Like most nitrous cars, mine isn't breaking records on motor, but it is night and day differnet on the bottle. Slower on motor, faster on the spray.
Build a car with a goal in mind and optomize the setup for that goal.
05-14-2007, 02:44 PM
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Yes to the above. I have seen additional rwhp gains of 60-70hp on nitrous when going to a nitrous cam when using a 250hp shot. OTOH, this is not to say that a good NA cam won't work with nitrous, it will work. Just that there are additional gains (at some cost) with an N2O specific cam.
Rich
Rich
05-15-2007, 02:46 PM
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Specs for a "mountain motor" cam designed for large ci and BIG nitrous.
318/352 285/312 .846 .810 116°
Note the huge split between the exhaust and intake durations (34 deg adv and 27 deg at 50). Installed on a 110ICL (6 deg advanced) the exhaust opening point is 118 deg BBDC!!! This illustrates what the point that early exhaust opening is needed to optimize nitrous use. In this case, a very efficient induction system is also present and adds to the need to open the exhaust early.
With a blower, though large amounts of combustion gas also needs to be exhausted, the positive manifold pressure can be used for this purpose and very early exhaust opening is not needed, at least to this extent. In effect, boost is used to blow the exhaust out. Too much of this is bad, but some is inevitable and desirable.
Rich
318/352 285/312 .846 .810 116°
Note the huge split between the exhaust and intake durations (34 deg adv and 27 deg at 50). Installed on a 110ICL (6 deg advanced) the exhaust opening point is 118 deg BBDC!!! This illustrates what the point that early exhaust opening is needed to optimize nitrous use. In this case, a very efficient induction system is also present and adds to the need to open the exhaust early.
With a blower, though large amounts of combustion gas also needs to be exhausted, the positive manifold pressure can be used for this purpose and very early exhaust opening is not needed, at least to this extent. In effect, boost is used to blow the exhaust out. Too much of this is bad, but some is inevitable and desirable.
Rich
Last edited by rskrause; 10-15-2007 at 08:54 PM.
05-15-2007, 03:14 PM
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Rich,
I just made this a sticky with one caveat. I'd like to addthat though this is very good information, that answers some common questions regarding Camshaft(s) for Nitrous applications, my general opinion is that maybe 1 out of 100 combinations require a camshaft designed specifically for nitrous. These generally being cars that are running multiple systems trying to add well over 350-400hp...
I just made this a sticky with one caveat. I'd like to addthat though this is very good information, that answers some common questions regarding Camshaft(s) for Nitrous applications, my general opinion is that maybe 1 out of 100 combinations require a camshaft designed specifically for nitrous. These generally being cars that are running multiple systems trying to add well over 350-400hp...
Last edited by KTamez; 05-15-2007 at 03:37 PM.
05-15-2007, 03:28 PM
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Rich,
I just made this a sticky with one caveat. I'd like to addthat though this is very good information, that answers some common questions regarding Camshaft(s) for Nitrous applications, my general opinion is that in all but maybe 1 out of 100 combinations require a camshaft designed specifically for nitrous. These generally being cars that are running multiple systems trying to add well over 350-400hp...
I just made this a sticky with one caveat. I'd like to addthat though this is very good information, that answers some common questions regarding Camshaft(s) for Nitrous applications, my general opinion is that in all but maybe 1 out of 100 combinations require a camshaft designed specifically for nitrous. These generally being cars that are running multiple systems trying to add well over 350-400hp...
Rich
08-16-2007, 04:38 AM
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It will work fine, as nitrous does with almost any cam. The issue with nitrous specific cams is primarily where people want to optimize the car for nitrous - typically a setup with large amounts of nitrous used for racing. For practical purposes, unless you are spraying 300+hp, don't worry about it. OTOH, even using a "regular" cam, if you are interested I would suggest installing it with a couple of extra degrees of advance if you use nitrous a lot. Little will be lost and you may see an additional 10-30hp on the nitrous.
Rich
Rich
Last edited by rskrause; 10-08-2007 at 07:22 AM.
08-16-2007, 12:58 PM
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I think you might have missed a key point in Rich's post.
At your level of nitrous consumption/usage, the cam won't have much effect. A 100-150 shot that loses 3-5% is only losing 5-8 rwhp. That effect is compounded as the amount of nitrous goes up.
As for the second cam you listed. It looks like a decent nitrous grind with lots of exhaust duration. A 112 would be a reasonable middle ground for a 200 or less shot.
At your level of nitrous consumption/usage, the cam won't have much effect. A 100-150 shot that loses 3-5% is only losing 5-8 rwhp. That effect is compounded as the amount of nitrous goes up.
As for the second cam you listed. It looks like a decent nitrous grind with lots of exhaust duration. A 112 would be a reasonable middle ground for a 200 or less shot.
10-08-2007, 07:30 AM
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The subject of "optimized" cams came up the other day at the shop. A couple of very experienced people were there. There is something mentioned in the original post that came out as very important when trying to compare cams. Nost cams are very far from optimum, so when you do a swap (whether it's on a blower or N2O or NA car) a lot of the gain comes from characteristics that have nothing specifically to do with blower or nitrous use but just because the cam is better for the application in the first place.
I don't think I am being to clear, so I will try an analogy. People report huge gains from swapping plugs and wires. Part of this is the power of suggestion. But part is real. Except it isn't that one brand of wire or plug is so superior. It's that the old ones were worn out, so any new brand swapped in would be a big improvement. So, swapping in a "nitrous" or "blower" cam can give a big improvement just from a more optimum duration and lift and LSA, even though the cam is otimized for a specific use, it is still closer to the NA optimum than what was in there.
Rich
I don't think I am being to clear, so I will try an analogy. People report huge gains from swapping plugs and wires. Part of this is the power of suggestion. But part is real. Except it isn't that one brand of wire or plug is so superior. It's that the old ones were worn out, so any new brand swapped in would be a big improvement. So, swapping in a "nitrous" or "blower" cam can give a big improvement just from a more optimum duration and lift and LSA, even though the cam is otimized for a specific use, it is still closer to the NA optimum than what was in there.
Rich
Last edited by rskrause; 10-15-2007 at 08:54 PM.
10-15-2007, 08:52 PM
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Rich