swinger340
Well-Known Member
I know that a cam w/ .525 advertised lift w/ 1.5 rockers has .350 lift @ cam and would be .560 lift w/ true 1.6 rockers. Does the duration change as well or stay the same?
1.5s to 1.6s change cam duration???
- Thread starter swinger340
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According to Comp Cams,usually about 2 degrees @.050 for each ratio jump.
Abody Joe hit it best and on the head. This change of duration is a minor one. The more radical lift of the rocker jets the valve open a little sooner, that is it. Do the change for the lift increase, not the cam increase.
swinger340
Well-Known Member
Thanks guys. My solid flat tappit cam specs are .525/.535 lift and 240/246 duration @ .050 looking for more lift but dont want to change duration all that much. going in 10.3:1 340 RHS heads. Once i subtract the .020 lash i am only getting .495/.505 @ the valve. My 1.5s are more like 1.47. Probably be fine for a street strip motor but i was hoping for a little more actual lift.
Run tighter lash.
femtnmax
Well-Known Member
One of the magazines did the 1.5 to 1.6 rocker swap using OEM heads, did not work out for hyd cam due to heavy weight of 3/8 valves. About a year later the same magazine(?) did a build with 1.6 rockers and newer style heads with smaller valve stems (less weight) and they had no problems at all running hyd cam.
I know your running solid lift cam, but doesn't hurt that you have newer lighter weight valvetrain.
D.Vizard says 1 point rocker change = 3 degrees increased duration at .05 lift, and 7 degrees duration at 0.20 lift.
I know your running solid lift cam, but doesn't hurt that you have newer lighter weight valvetrain.
D.Vizard says 1 point rocker change = 3 degrees increased duration at .05 lift, and 7 degrees duration at 0.20 lift.
Duration at the cam doesn't change. The duration at the valve does.
Measuring at the valve, .100 lift. A 1.5 rocker, lobe has to be off the base circle .0666 to get you .100 lift at valve. With a 1.6 rocker, the lobe lift is .0625.
Measuring at the valve, .100 lift. A 1.5 rocker, lobe has to be off the base circle .0666 to get you .100 lift at valve. With a 1.6 rocker, the lobe lift is .0625.
swinger340
Well-Known Member
How tight can you go on solids? The recommended lash on this particular (custom ground comp.) is .020/.020. I was thinking w some 1.6s that may actually only measure 1.55 or so i can get the lift in the .522/.533 area.
daredevil
Well-Known Member
I agree with this somewhat at lift duration changes but total duration doesn't. Duration is ground in the cam and begins and ends the same place regardless of rocker ratio if lash is the same. Why does a tighter lash decrease duration? Seems it would accelerate the action of the duration of the cam because not as many degrees would be lost while the play was being removed.
You can try varrying it both tight and loose. Those specs are really more for a guide than anything. Since all engines are different, you may experience your best power adjusted differently than what the card recommends. Since you are already pretty wide at .020" I would try maybe .010" or .012" on both sides. It wont hurt a thing.
MoparAnglia
Well-Known Member
You're right but total duration isn't what's being referred to here. And it tends to be a far less useful number to apply to anything.
You're right about the tighter lash too, but the goal is increased lift. He said he didn't want to increase duration TOO much.
fishy68
Tyr Fryr's Inc.
When I recently built my 408 I installed a small Racer Brown solid cam and my heads (EQ magnum style) use 1.6 rockers so I wondered just how much difference it actually makes at the valve, which contrary to belief to some is what matters. So I set up my degree wheel and dial indicator and very carefully took readings at the valve to see how much gain the 1.6 rockers produced. BTW: the rockers I used are Harland Sharps and I verified their accuracy by measuring the cam lobe lift and comparing it to the valve lift. In the end I found my cam that was rated at 236 @ .050" now produces 239-240 degrees at .050" valve lift. I ran through it 3 times to make sure I got repeatable #'s and every time my readings were within 1 degree. Therefore I have to agree with those that said 3-4 degrees gain at .050" valve lift.
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