Was reading an article on a big block chevy hydraulic roller cam that was ground with small block chevy HRC sized lobes. This reduced the base circle diameter and allowed them to run higher lifts without chucking the anti-rotation plates. Since the lifters ran lower in the lifter bores on the smaller base circle there was more distance for the lifter to move without hitting the retainer plate. The unfortunate thing about the article was that there was no exact numbers given to quantify the increase.

My question is: what is the difference in base circle diameters between the big chevy and small chevy HRC's and how much lift increase is possible over just using the standard big chevy cam base circle?

 

I have not yet seen this article. I do know that when Dart came out with tall deck raised cam small blocks, that you have to use a special cams with big block bearing sizes and standard small block base circles.

The raised position of the cam and tall decks kept all the rest of the valve train standard available hot rod stuff.

 

got a link???? i'd like to read

 

Here's the link:

http://www.chevyhiperformance.com/techarticles/93620/

I spoke to a guy at Howard's cams yesterday who told me that the base circle for a roller cam is based on the lift. The nose dimension stays the same which is based on the cam journal diameter. The base circle is then ground smaller to make a cam with higher lift. I may have mis-understood the article not knowing that. The guy at Howards told me that all of their big chevy profiles are based on the nose dimension for BBC's. I don't see why you couldn't base the nose dimension on a smaller cam lobe like a small block chevy, though (or even a reduced base circle small Chevy). The roller diameter (in fact most everything else) is the same. Howard's said they never had a request like that because BBC's don't normally require reduced base circles due to plenty of conn-rod/cam lobe clearance.

My whole thoughts are that I have a MarkIV block that I want to fit a GenVI valve train to. If the cam base circle (and nose) are reduced slightly, the taller GenVI lifter can fit in the MarkIV cam bosses without the oil groove pushing out above the top of the boss.

Retro-fit rollers are so damn expensive, yet GenVI components can be picked up relatively cheap. I can't see why some cam grinders don't pick up on this, making the cost of a roller cam setup relatively inexpensive.

GKULL, have you dealt with any custom cam grinders that might be willing to discuss this with me??

Thanks.

 

thanks