Ratio rockers stock cam?

[Raging Bull Engines]

To see what the rocker arm change did you would either check it on that end of the rocker or the retainer, i never check anything at the lifter side. I agree with KB63 and CH it increase duration over the whole curve, its harder to measure at low lifts .010-020 range but you would be able to see it as the numbers get greater.

As long as you are measuring on the valve side of the rocker arm, you could measure either right on the rocker arm or the spring retainer and they should be very close. Just don't measure on the pushrod side of the rocker arm because that would be measuring only the cam profile (negating the ratio rockers). Of course, this all applies only if your definition of duration is at a measurement other than "off the seat ". At "off the seat", the ratio rockers are not affecting lift. Duration measurements taken at .020 or .050 or any other lift height, the duration will be higher (longer).

Higher ratio rockers change the duration more at higher lifts.. The duration gain will be less at .050 lift than what it would be at .150 lift. Here is a graph comparing duration at the valve at various lifts on a V8 camshaft with 1.5 vs 1.6 rockers. notice how the gain is more at higher lifts.

1.5 rocker w/.018" hot lash
316 seat duration
294@.020"(net valve lift)
272@.050"
248@.100"
213@.200"
182@.300"
152@.400"
117@.500"
067@.600"
.648" net valve lift

1.6 rocker w/.019" hot lash
316 seat duration
295@.020" +1
274@.050" +2
251@.100" +3
217@.200" +4
188@.300" +6
160@.400" +8
128@.500" +11
089@.600" +22
.691" net valve lift +.043"

 

[Petty Race Engines]

Don… in tech I always check the duration at .200 lift not the .050 (in spot check tech, not full tear down) because of this very reason, if you tweak a stock lifter to gain ratio, it will not show up as much in degrees as much as it will at the .200 check, if it passes at .200 then 99.9% the .050 check is good..

 

[DynoDon]

I agree.Hence the cl4 NKA cam

 

[kartboy63]

yep