so rockers dont effect duration at all? how is that? im pretty sure if the cam was at .500 lift at a certain spot and with stock rockers its at .460....then when the valve closes with stock rockers its still for .040 left to go...meaning its open a little longer
pretty sure rockers effect every aspect of the cam....


since theres no back to back comparison im not sure if im going to do them they seem to not be worth the hassel...plus i dont like the only choice we have for 1.7 they are heavy and bulky...think im just goana do 1.6 nsa pr mags with 7/16 studs and guideplates with arp studs and call it a day...debating now what i wanna do for springs prolly do crane 10308's
is that too much springs for only rockers with a stock cam? anyone also any new choices besides the scropians?(sp)

 

"Duration" as usually described is defined on the cam side. So, technically speaking changing the rocker ratio does not change duration. However, looking at the valve side it is different. The seat timing is not changed with a different rocker ratio. But increasing the ratio will increase the duration at the valve at any other point on the lift curve. So, effectively speaking, the duration is increased without changing the seat timing.

It might be worth trying. But be aware of the potential for pushrod clearance issues. There also may be inadequate piston to valve clearance. Also, finding a spring that would work with stock length valves is another issue. You need to consider both coil bind and retainer to valve guide clearance. IOW, it may be a simple bolt on, and it may be a big deal to get them to work.

Rich

 

As stated, changing rocker ratios will not alter the amount of time the valve is open or closed, but does increase the speed at which it is opened and closed.

I didn't realize the term 'duration' referred to both the time the valve is off the seat and the rate of acceleration it is under during motion.

Thomas.

 

It sounds like we both know what is happening, so this is semantics. If you describe "duration" as referring to the number of degrees the valve spends at various points above the base circle it DOES increase with a higher rocker ratio. I don't know what to call this except "duration". In terms of what this does to performance, in genreal it has only positive effects provided the valve train geometry can accomodate it. Pro Stock is now using up to 2.0:1 rockers, I believe. There are a couple of reasons this is preferable to using bigger cam lobes. These include the strength of the cam (a smaller base circle is needed for more lift) and the spring pressure needed to control the valve train. In general, it is always a good idea to increase the rocker ratio. However, there are limits of mechanical interference I referred to earlier as well as considering the added strain a higher ratio puts on the valve stem and guide. Going up one ratio is usually not a problem. Two or more may be, what we are talking about here.

Rich