Posted 19 March 2009 - 10:16 PM
Info from SBD motorsport website;
We are often asked what up-rated cams do we & that can be just bolted on to a standard engine, without taking it apart. To save yourselves & us a lot of time, here are the advantages & disadvantages of carrying out this operation: -
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.
The only other common question we are asked, is people running road cars e.g. Astra 2.0L 16V or Cavalier SRI & GSI even the modern Ecotec engines as fitted to the latest range of Vauxhall cars. What kind of camshaft can I fit to my car? As well as all the problems already listed, you have one further problem to add and that is, that most production cars use what is known as air-flow metering.
They are either what is called ‘hot wired’ where the air being drawn across a heated wire changes the resistance according to temperature. So the faster the air, the cooler the wire becomes and from this the standard ECU is able to work out the amount of air being drawn across the air-flow meter.
The other type is what we call a ‘gate type’ and the faster the engine draws the air, the gate being sprung loaded, is sucked open further. Now for the problem – all camshafts generate a pulsing effect, this is where at a certain point in the engine cycle the inlet charge becomes stationary (for simplicities sake). On a mildly tuned engine e.g. standard, this stationary pocket of air remains very close to the cylinder head. As you attempt to increase the cam duration on overlap to generate more power, this stationary pocket of air moves further and further up the inlet tract, eventually reaching the air-flow meter. Once this happens all air-flow metered systems become completely confused. So if you fit a camshaft which is a great enough improvement to give you an increase in performance, it will almost certainly produce the described effect and if you fit a camshaft mild enough not to cause the effect, your gains will be almost insignificant.
You might say, why not move the air-flow meter further away? Problem 1 is the reason most road cars are sluggish on throttle response is because the airflow meter is so far away from the head to begin with. The manufacturer has carefully worked out the position, which is as close as possible to the engine without causing the effect described. The further away you move the airflow meter the slower the throttle response becomes. So in effect, any gains you might have got from changing the cams is completely lost by the increasing delay of throttle response.
The only kind of system that can cope with this pulsing effect, is a throttle angle system such as the MBE systems we supply. They are pre-programmed with an amount of fuel for every at various speeds and throttle openings and as such are not effected pulsing. There is also no delay because whatever speed you are at, and whatever throttle angle you achieve, the ECU knows immediately the pre-programmed amount of fuel to deliver.
So as you will see from our Engine kits, if the replacement cams are used they are fitted in conjunction with either, deepening of the pockets of the standard pistons or replacement of the piston with up rated piston with deeper pocket & higher compression
) for more topend. I dont find the thumping 340lbft overboost to be too friendly tbh. Here is a dyno plot i found, this is both x20xev NA cams in the Z20LET on std timings
:D:D:D glad you like my cut and paste late at night 
