" There's a lot of things that were all the rage over the years that when modern analysis was applied, were proven to be not effective or harmful. There have been things that became "standard" that are still done to cylinder heads that actually hurt them as far as flow is concerned. I actually debated with myself before posting as this is one of those subjects that's a lot like politics or religion. Arguments almost always ensue. One side says "I've done it and it hasn't broken therefore it is good" and the other side picks it apart and asks "why is it good or bad."
The common consensus in the OEM and racing world is that you lose oil volume and pressure to the rod bearings at higher RPM's. There's some good, published work by TRD engineers out there on the net, but there's also a lot of info that trickles from the racing industry. The bottom line is, if you don't have an oiling problem, cross drilling is not needed and will not help the situation. If you have an oiling problem, before you cross drill you need to figure out why you have the oiling problem. What cross drilling can cause is aeration of the oil and reduction of volume to the rod bearings. Overcoming centrifugal forces getting oil to the gallery connecting to the rod journals requires higher pressure and increased volume to overcome that tendency.
Mind you, this is an issue that comes at much higher levels of power than many people see. There have been a number of cross drilled crank engines in high levels of competition over the years that did well. There are also engines that had problems that resulted from using one. The key is, if you aren't having problems, don't try to fix something that isn't broken. Cross drilling was originally done to try to help with flow to the rod bearings. At high RPM it starts to take away flow from the rod bearings unless the pressure and volume are increased. If the pressure and volume are increased, the rod bearings get more oil at an increase of parasitic loss required to make more oil pressure.
It's an argument with no end as it can be made to work either way. In a "stock" type oiling system, running a cross drilled crank will decrease oil to the rod bearings at higher RPM. If you use a full groove main bearing, you get more oil to the rods at the expense of hydrodynamic wedge in the mains. If the power level is such that full groove main bearings work, then it's all a moot point. If you start to kill main bearings, then you can experiment with 210 degree bearings or try more volume through the system.
It's like anything else in the performance world. You trade something for something. Nothing is a magic bullet unless all the ramifications are allowed and compensated for. A lot of things in engine building get done simply because "so and so said so". I've done things that customers wanted simply because they were listening to their friends and people on the forums. I'll do them as long as I don't feel they'll hurt anything, but try to steer them away if I think it will end up hurting things in the end.
I attended the School of Automotive Machinists a year and a half ago to learn what industry was doing and try to keep abreast of the state of the art while learning to build current tech race engines. I subscribe to Race Engine Technology and read everything I can get written by Gordon Blair and Don Terrill. I'm by no means an expert on engines, but I do analyze everything to try to understand the "why" when someone says to do something. I'm one of those born skeptics that wants a reason for everything I guess!
I don't want to step on anyone's toes, as there are plenty of people on both sides of the issue. Like I said, I debated before posting in the first place. "
Taken from: http://theamcforum.com/forum/cranksh...734_page1.html
And this: http://rehermorrison.com/tech-talk-5...calls-part-ii/
So now I'm not sure if it is such a good idea to use if you want to rev the engine past the original 7300 rpm
Although there they are talking about cross drilling cranks that aren't cross drilled from the factory.
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will let us know from what engines the old type crank was and if they were used on early 7A engines.
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