LSx cam design difference from Gen I SBC

[pparaska]

I was reading an article on the LS7 heads by Vizard:

http://www.gofastnews.com/board/technical-articles/261-7-liter-corvette-heads-can-they-improved-upon.html

 

and found the following quite interesting:

"Fortunately the LS range of engines is well situated to do just that far more effectively then a traditional small block Chevy. The key factor is the LS’s design of roller lifter cam and valve train. When the factory decided to go roller only they were smart enough to design the cam with a much larger base circle than any GM engine that had gone before. The significance of this is that the bigger the base circle is the lower the pressure angle the roller lifters experience for a given lifter acceleration.

 

Unlike a flat tappet cam a roller cam has a significant side load. The steeper the pressure angle the higher the side load. More lifter acceleration means more side load while a bigger base circle on the cam and a larger roller both reduce the pressure angle on a lifter for a given acceleration.

 

The higher the pressure angle the greater the side load on the lifter. A sane limit is about 28 degrees. This side load puts a limit on how fast the lifter can be accelerated. If either the lifter roller or the cam’s base circle is increased the pressure angle is reduced thus allowing for an increase in lifter acceleration by employing a steeper lobe on the cam profile until the pressure angle limit is once again reached. The sizing of the LS’s components in this area allow for a far faster lifter rise then the old small block. This means that our 427 has a much increased potential for faster valve opening and, if we add to the fact that it has a light titanium intake valve, it is in an even better position yet to successfully employ very high valve lift numbers. This ultimately means the engine is in a strong position to access the increased flow seen at high lift."

So, if you didn't know before, this is one place (other than a light block and a great head design) that the new SBC (LSx) is better than the old SBC - The larger cam base circle allows a more aggressive valve opening for the same pressure angle limit for roller lifters.