F.A.T. PERFORMANCE 01

I installed a Lingenfelter GT1 cam 218/229 560/560 with a set of crane gold 1.8 roller rockers. I need to know how i figure what the lift and duration would be with the 1.8 rockers compared to the stock 1.7s, or if you know what it would change it to. I am not having any problems just curious what it would be. I really like the way this cam sounds it has a mean lope to it, not sure about performance yet i still have to have it tuned, but it sounds great.

Thanks
Nathan

someday

divide the .560 by 1.7, then multiply by 1.8
.560 / 1.7 = .329 lift at cam...
.329 x 1.8 = .592 lift at valve...
the duration will change very little, maybe 1 or 2 degrees...

Jabroni

My understanding is that the rockers are a valve lift multiplier only. Duration shouldn't change at all.

Jason99T/A

iTrader: (21)

The rockers will change the duration at the valve slightly. The duration @ .006" will not change much, if any, but the duration will increase proportionally as the valve opens further.

The duration @.050" is only changed ~2-3 degrees.

ls1290

iTrader: (20)

I am sorry, but I do not see how different ratio racker arms will change the duration of the cam. The width of the lope is still the same, just the height of it is increased by the rocker arms.

Vents

iTrader: (9)

ls1290,

that is true that the lobe does stay the same, however, the rocker arm is a multiplier, since it is not a true 1:1 ratio. going w/ a 1:8 as opposed to a 1:7 will bring the ratio upwards. this not only changes lift but duration slightly as well.

HR had a great write up on a similar subject a while back. somone was using these larger diameter jesel roller lifters in a BBC. by making the diameter of the roller larger, they effectively added in a few extra degrees of duration to a cam. kinda works both ways. anyway, those are simply examples of how small things effect the bigger picture. but hopefully ya get the idea.

F.A.T. PERFORMANCE 01

Thanks guys i appreciate the info. I was led to believe that the different ratio would change the duration slightly due to the extra lift.

Visceral

iTrader: (1)

ok...this depends on how you define "duration". Duration is normally rated at .006 and .050 *lobe lift*. Hence, the rocker would not change the rated duration of the cam.

Now, how do rockers change the way that the valve "sees" duration? For a given valve lift, a .1 increase in rocker ratio roughly increases the .100 valve lift duration about 2 to 3 degrees. You will primarliy see that as a slight increase in overlap between intake and exhaust lift (changing the sound of the cam slightly). Because the ratio is just that, a ratio, there is no duration added where there was NO duration before. Increasing rocker ratio adds power by increasing lift in a proportional manner. Where there is more valve lift, the rocker proportionally adds more.

HTH...

chris