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Ben,
Let me add that I think its great that you spent the time to put all of that info together graphically. It really shows clearly what some of the problems and issues are that cam designers have been working on for the past 100 years. Its good for all of us to have an understanding of these issues but we have to rely on the experts for whom improving cam design is a profession. The process for them is one of extensive rounds of design, execution of prototypes, and extensive testing for each specific application. Change the exhaust system, or even the gearing and a different cam might be a better choice.
Each issue you have pointed out involves compromises where other factors such as metalurgy, lubrication, and the specific cam application are important. You can design a different lobe profile for a racecar, for example, that is going to have the cam changed frequently, as opposed to a car that is designed to go 100,000 - 200,000 miles on the same cam. The cams and lobes are designed to minimize wear, and a key factor in this is shapes that will provide for continuous rotation of the lifter and keep contact pressures within certain parameters. The actual pressure of the lifter on the cam is a key as are the materials and hardness of the components.
Another issue is the valve train and its components. The lifter has to be able to follow the cam lobe shape. In fact the actual path of the lifter may not be the actual shape of the lobe. You can see from your diagram that the only thing that prevents the lifter from flying off the end of the cam is valve spring pressure. Not enough pressure and the lifter does not follow the cam. Too much spring pressure and the cam and lifter can be overstressed resulting in high wear or premature failure. The spring pressure needed is highly related to rpm and several other factors includig the rate of acceleration of the lifter on the cam lobe. For race applications we use double or triple springs that are much larger in diameter than stock and may have almost twice the spring pressure when the valve is open. With these springs we can use a much more aggressive lobe shape, but the spring pressures necessary just would not work on a street engine.
The issue of lifter shape that you raise was first "solved" with the mushroom lifter that is larger on the bottom - the shape of an upsidedown mushroom. The better solution is the roller lifter that can be found on most modern cars with lifters. The roller on the end of the lifter allows for a completely different cam lobe profile. There have been b20 cams done for roller lifters, but to my knowledge there are none available today. If someone out there knows of someone who is or can do them, please let me know. One of the problems here is that race use would usually be the place where there would be the greatest demand,and people would be willing to pay the cost, but most if not all organizations who sanction vintage/historic races and rallies have rulled that roller cams and lifters are a non periord modification that will not be allowed. They were being used in the UK a few years ago with great affect.
So there are solutions that are out there. Applying them in an economical manner to an engine design that is coming up on being 50 years old is the real challenge, not trying to design new solutions. A lot of this boils down to economics. Those of us who are in the business of supplying performance products for your cars need your support. We can't spend a lot of money designing and testing improved cams, for example, if we are only going to sell a few a year. Every time a Volvo owner makes the decision to buy a D cam, or one of the Isky cams that was designed 30 years ago and have been sold mainly by IPD, because it is $100 - $200 cheaper than one of the new performance cams and "is almost as good", that hurts the process. If I could sell 100 cams a year the price would be $50 - $100 less per cam, my profit on cams would be be higher ( which would be easy because there isn't any now), and it would make sense to spend more time in cam development. Because of the time it takes to do the necessary testing, we usually only come out with one new cam grind per year, and that is divided amoung normally aspirated street cars, supercharged street cars, and racecars.
All of the companies that still deal in Volvo performance parts, and especially those that still do development work rather than just sell old products, need your support. The reason that there are more parts available for vintage Porsche and BMW owners, for example, is that they spend more to support companies that provide products for their cars. Its not because there are more of their cars out there. The problem for us is trying to provide performance products on a very limited budget. I know exactly what has to be done to get very significant improvements in performance for B20 engines.
I actually have an offer on the table TODAY for a product that would be unbelievable if we could do it. It could be ready and available in less than 6 months, but the estimate is that it would cost in the range of $50,000 for the basic development work, tooling and patterns, before production of each item. If this was for a Porsche it would be great as we know the market is there, but for old Volvos, at this point I have to pass.
Now back to work.
John
V-performance.com
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