Right from the first, let me state that i'm no camshaft engineer or expert. I'm just interested in the subject, so any extra information or corrections will be gratefully received. Choosing a camshaft grind is much like choosing a shirt - they are many and varied to suit different situations and needs! I have managed to compile the following rather long list of possible cams - not to tell you what to use, but rather to tell you what is available. After talking to some of the club members listed about the cams and also to the manufacturers, you may then be able to choose a cam to suit your needs. The cams available from each manufacturer are arranged (as near as I can work out) from "mild to wild".
Generally speaking, a cam's performance can be estimated from both its Valve Overlap and the lift of the cam. The Valve Overlap (in degrees) is the period when both the inlet and exhaust valves are open at the same time at the top of the piston stroke - as the exhaust valve is closing and the intake is opening. The lift controls how far open (or down) that the valves will be pushed. The larger the number of degrees of valve overlap, the higher the engine will be able to rev (all other components being developed to suit). The higher the lift, the greater the acceleration, with suitable carburation, etc. Naturally, the period that the valves are open affects both the above factors, but a longer valve period usually goes hand in hand with those factors.
So, why does a high-revving cam have to be a larger Valve Overlap than a standard cam? Essentially it's because the fuel/air mixture waiting in the inlet port behind the valve has a certain amount of inertia or "slowness to get moving". As the engine revs increase, the piston speed increases (remember, the downward movement of the piston sucks the fuel/air mixture into the cylinder). However, the inlet gas has a maximum speed and always the same amount of inertia, so eventually the piston speed will exceed the maximum speed of the gas, and the cylinder only gets partially filled - then the power starts to drop off. Therefore, high performance cams are designed to give the gas a "head start" on the piston, by opening the inlet valve many degrees before the piston gets to the top of its exhaust stroke (T.D.C.). Also, this valve is closed many degrees after the piston has gone past the bottom of its stroke because the gas will continue to enter and more tightly pack into the cylinder. Similarly, the exhaust valve opens way before the piston gets to the bottom of its power stroke, to start the expanding burnt gases moving out earlier. The valve is then closed many degrees after the piston has gone past the top of its exhaust stroke to allow the gases to continue to rush out. remember that the valves do not open and close instantaneously, but gradually. In the mid-rev range, the inlet gases as they start to enter, aid in pushing out the burnt exhaust gases whilst the exhaust valve is still closing after T.D.C. With high performance cams at low idle speeds, a spitting back through the carburettor occurs when the inlet gas is pushed back through the inlet port by the rapidly expanding exhaust gas - because of the relatively slow speed at the piston, and because the momentum of the exhaust gas is not sufficient to keep it moving on out through only the exhaust valve.
In fact, with some "3/4" to "Full race" cams, the engine may be as "dead as a Dodo" and have virtually no pickup below say, 3,500 to 4,500 revs (particularly with large ports). Wade make a competition cam with the valves of cylinders 2 and 3 offset by 5 degrees which makes the engine run smoother at all revs, it picks up better at low down and does not spit back through the carbies. So the greater the rev potential of a cam, the greater the valve overlap (but the rougher the idle and low speed running). Remember also, that as the overlap increases, the fuel economy will decrease, particularly at low revs.
But is it worthwhile getting a cam with high lift? This depends on what you want, but 'A' series BMC motors thrive on high lift cams because they have a very long stroke and when the high lift cams are used the engines generally put out more power than would be expected with any other type of engine. Naturally though, with very high lift camshafts, the valve faces a seats sufer a little more "hammering" which mean that the valves wear further into the head, so the tappets will close up and to be re-set more often otherwise the valves will burn out as the closed-up tappets hold the valves off their seats. However, resetting tappets a little more often is a small price to pay for the greatly increased performance.
High lift cams in some engines (especially those with larger exhaust valves and/or those that have had the head or block shaved) may need to have the block recessed to allow the valves to have sufficient clearance. However, 1275's have plenty of clearance. This can be checked by partly fitting the head and placing some plasticine on the valve face (with all other tappets slackened off) and then slowly reducing the valve cleaance to the required amount, then allow another 0.030" for bounce and clearance and check the indent in the plasticine - this saves bent valves! An extremely high lift cam (as on racing cams) greatly increases the strain and wear on the components of the valve "train" (the valve faces and seats, valve springs, rocker faces, cam followers and cam lobes). This is why it is recommended with these race cams to fit larger diameter Holden cam followers to greatly reduce cam and follower wear.
Diferent cams have different rates at which the inlet and exhaust valves open and close. The "ramp" of the cam lobe may gradually and evenly open the valve, open the valve very suddenly, start to open gradually and then finish opening quickly (or vica-versa), or any combination in between. The same number of possibilities exist for the closing ramp (and it may not be the same profile as the opening ramp). This rate of opening and closing of both inlet and exhaust valves has a lot to do with the harshness or smoothness of the operation of many cams and also the expected life of the valve train. Thus, 2 cams can have exactly the same timing and lift specifications, but they can operate as totally different cams (there are some like these in the following list).
Anyway, perhaps the most important question we should ask is - do spridgets need a better designed or more "sporty" camshaft for normal road use? Interesting question! If we look at the sedans produced by bMC-Leyland with the same motors, we find that they are fitted with the same camshafts. the Cooper 'S" and other Mini Coopers have more sporty camshafts (see list). When driving spridgets with standard camshafts, the engine is quite smooth and pulls progressively from low revs, but the acceleration is not startling and the engine quickly runs out of "puff" in the medium to higher rev range.
Having digested all this information, my answer to the first question must be "Yes" - provided we can retain the smoothness and low down torque of the standard cam as well as reasonable fuel economy. This can be achieved with a number of camshafts in the list - particularly those of, or equivilent to, the Mini Cooper cams. There are many cams suitable for the various mid-range uses that you as members may have, and there are also a few good cams to choose from for out-and-out racing. However, I'm reluctant to give you any of my cam recommendations (especially when I started by saying I wouldn't do that) because I have had experience with only about a dozen out of that long list. Anyway, for what they're worth, here are some cams that you may like to try (refer to the list for details and comparisons). Don't forget to talk to other club members about any cam in the list in which you may be interested.
I personally would not be bothered with using any cam in between those mentioned above. Anyway, I hope all of this blurb is of some help to you when it comes to your engine rebuild. But remember, DON'T just pick a cam, put it in and do nothing else to your engine - think about the total engine and what else will be needed to get the best performance out of that cam for your requirements. Don't be afraid to seek the advice of other "Old Hands" in the Club about your engine rebuild.
I have included as many cams specifications as I could find from the following manufacturers:
If you have the specifications for other brands/cams, please send via email it to the site maintainer and we'll include the details. Feel free to comment on your experience with any of these cams!