Probably one for the geeks. Just read this on a tuners website is it saying that cam upgrades, on there own, are pointless on modern 16V engines?
"1. On almost all modern 16 valve production engines compression ratios are quite high to aide combustion for low emissions & the way the compression is kept high is to not to keep piston pockets to a minimum. This unfortunately allows little if any room for increase the opening of the cam at TDC (which is the easiest way to generate extra BHP by using the exhaust gases to help draw in the next charge).
2. The Designers of modern combustion engines are also being asked to make them smaller, lighter, as well as being cheaper to produce. So the room for increasing the cam lift with out replacing the valve springs is usually quite small.
3. Because of the problems mentioned in 1 & 2. The gains are usually quite small for money spent. The way you can attempt tuning your standard engine just by cams changes are.
a. The use of Group N Cam profiles these are normally used in cars where the Championship rules specify that standard cam profiles must be used. But the FIA & most other motor sport governing bodies give a tolerance which is usually + or – 2 Degrees on the duration & + or – 0.2mm on the lift. So these are taken advantage of on special ground profiles that are extremely accurately ground to the upper limits of these tolerances. But unfortunately the gains from this type of profile are very small. In Group N type Championships though, any small gain is always worth having, but for any other competition where such rules do not apply we would not recommend this type of profile.
b. The second type of profile is sometimes called a group N+ profile. These are designed for championships where the rules state your engine must retain standard or near standard valve lift, no modifications are allowed to the standard piston pockets, but cam duration is free. The problem with this type of cam is because of the restriction caused by the valve to piston pocket clearance. Usually they are very special cam profiles, which have been designed with very rapid valve opening to take maximum advantage of the limited space available. The problem with this is that they have to be very carefully run in, are not suitable for high mileage use & must be very accurately timed to avoid valve to piston contact. Again only recommend where regulations force their use.
c. The last & most often attempted way of fitting an up-rated cam is to use a profile, which is quite mild on acceleration with a mild increase in duration over the standard cam. The problem with this is as stated before, due to the lack of space the new cam profile cannot be timed to its optimum. This will give 1 of 2 similar effects. Either a huge loss in bottom end torque & only a small increase in peak power, over the original cam. This usually occurs if the replacement cam profiles have to be Retarded a long way (to avoid piston contact) because their duration is a lot greater than the standard cams. Or if the new profile is mild enough to fit with only slight retardation the effect is almost the same accept the loss in bottom end torque is not as great & the gain in peak BHP is almost not worth having."
"1. On almost all modern 16 valve production engines compression ratios are quite high to aide combustion for low emissions & the way the compression is kept high is to not to keep piston pockets to a minimum. This unfortunately allows little if any room for increase the opening of the cam at TDC (which is the easiest way to generate extra BHP by using the exhaust gases to help draw in the next charge).
2. The Designers of modern combustion engines are also being asked to make them smaller, lighter, as well as being cheaper to produce. So the room for increasing the cam lift with out replacing the valve springs is usually quite small.
3. Because of the problems mentioned in 1 & 2. The gains are usually quite small for money spent. The way you can attempt tuning your standard engine just by cams changes are.
a. The use of Group N Cam profiles these are normally used in cars where the Championship rules specify that standard cam profiles must be used. But the FIA & most other motor sport governing bodies give a tolerance which is usually + or – 2 Degrees on the duration & + or – 0.2mm on the lift. So these are taken advantage of on special ground profiles that are extremely accurately ground to the upper limits of these tolerances. But unfortunately the gains from this type of profile are very small. In Group N type Championships though, any small gain is always worth having, but for any other competition where such rules do not apply we would not recommend this type of profile.
b. The second type of profile is sometimes called a group N+ profile. These are designed for championships where the rules state your engine must retain standard or near standard valve lift, no modifications are allowed to the standard piston pockets, but cam duration is free. The problem with this type of cam is because of the restriction caused by the valve to piston pocket clearance. Usually they are very special cam profiles, which have been designed with very rapid valve opening to take maximum advantage of the limited space available. The problem with this is that they have to be very carefully run in, are not suitable for high mileage use & must be very accurately timed to avoid valve to piston contact. Again only recommend where regulations force their use.
c. The last & most often attempted way of fitting an up-rated cam is to use a profile, which is quite mild on acceleration with a mild increase in duration over the standard cam. The problem with this is as stated before, due to the lack of space the new cam profile cannot be timed to its optimum. This will give 1 of 2 similar effects. Either a huge loss in bottom end torque & only a small increase in peak power, over the original cam. This usually occurs if the replacement cam profiles have to be Retarded a long way (to avoid piston contact) because their duration is a lot greater than the standard cams. Or if the new profile is mild enough to fit with only slight retardation the effect is almost the same accept the loss in bottom end torque is not as great & the gain in peak BHP is almost not worth having."
