what makes a nitrous cam different from regular n/a cams?
05-15-2007, 10:37 PM
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what makes a nitrous cam different from regular n/a cams? i know a few friends with ls1 fbodys that run nitrous and have custom cams designed for spray, what makes these different from your regular run of the mill aftermarket cam? if this should be in another forum, feel free to move it
05-16-2007, 05:37 AM
#3
A cam optimized for nitrous (N) is quite different than a cam optimized for NA use. It will make a lot more power while on N, 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.
quoted from rskrause (cz28.com)
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.
quoted from rskrause (cz28.com)
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05-16-2007, 09:20 AM
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Originally Posted by daniel6718
A cam optimized for nitrous (N) is quite different than a cam optimized for NA use. It will make a lot more power while on N, 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.
quoted from rskrause (cz28.com)
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.
quoted from rskrause (cz28.com)
now a theoretical question.
couldnt u just run a slightly longer push rod on the exh side to help with duration and flow while on the hose?
05-16-2007, 11:34 AM
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Originally Posted by usd2sing
good info. thanks.
now a theoretical question.
couldnt u just run a slightly longer push rod on the exh side to help with duration and flow while on the hose?
now a theoretical question.
couldnt u just run a slightly longer push rod on the exh side to help with duration and flow while on the hose?
ummm.. no lol.
longer pushrod ='s exhaust valve open all the time depending on how much longer and how much preload the lifter wants.
**** if that was the case we would all just install longer pushrods rather than doing cam swaps
not trying to be a dick, just trying to be funny, sorta at your expense
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05-16-2007, 04:57 PM
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Originally Posted by badass68
Yea, people do that all the time on first gen SBC's.
this is why i asked the question.
it was a trick my father did on my roadrunner. (no n20 back in them days.LOL)
05-16-2007, 05:03 PM
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Unless your running a track car, just spec the motor to be ran NA goals, then spray on top of it. Thats one persons view. A traditional split cam is typical for sprayed cars.
