Help me to calculate on camshaftlift!!

[Olle B]

Hi
I take this easy way and try to find help on calculating the loss of lift I gain now that Im totaly without preload on my lifters due to a lot of mysterical circumstanses.
Im running a new Moparperformance orig RRcam with .450/.458lift.
I use hydralic lifters and they should be preloaded 0.04?
Mine are 0.005!!
I use original worn out 1.5 rockers.
Anyone can help me figure out what I loose in lift and maybe give some figures of what Im running with now!?
I also wonder what a 1.6 lifter with correct prepreasure will look like in liftfigures!!
Above .500?
I feel like the engine is "pumping air" and not so much to happen,,,,,but I just run the shit of my grandpaas Pontiac 1989 305" but what the heck,,,I mayby could do it with my old Volvo to!!

Best regards Olie B

[451Mopar]

In theory the hydraulic lifter will self adjust as long as there is some pre-load to give full lift. The real problem is with the old worn rocker arms, which usually have less lift (ratio) than the "advertised" 1.5:1.

To re-calculate lift with 1.6:1 rocker arms just divide 1.6 by 1.5 to get 1.0667, then multiply that by the cams advertised lift at 1.5:1 to get the new lift of 0.480"/0.4885" lift.

Or yot could divide the "advertised lift" by 1.5 to get the cams lobe lift, then multiply the cams lobe lift by 1.6, either way, it works out the same.

The part you can not easely calculate is how the rocker arm will change the cam duration (as seen at the valve) because the equivlent valve lift that was seen by the valve will occur sooner with the higher ratio rocker arm. For example, if you measured the cams duration at the valve when it is open 0.075" (the equivlent of 0.050" tappet lift with a 1.5:1 rocker arm) and the cams duration is 210, then you switched to 1.6:1 rocker arms and measured the duration at the valve again at 0.075", but now that is equivlent to 0.046875" of tappet lift, so the duration from that point may make the cam "look" a few degrees larger at the valves (maybe 2 or 3 degrees larger, it depends on the cams profile.)

[Olle B]

Hi
I was a little tired last(Swedish) evening so I thanks for your help.
Just wonder if the 0.04 preasure I loose will affect and give me a 0.04x1.50=0.06 lift or as you tells the lifter can take up the gap from start and the gap itself dosent affect the performance.
The gap maybe is just a "noise" problem!?
Intresting fact concerning worn original lifters,,,,are they less than 1,5? How much ,,or low can they be?
To be true,,I cant figure out any other reason why not having the correct preload than the rockers.
All is new,,cam,,lifters,,pushrods,,even milled 906 !!
Thanks
Olle B

[dirty dan]

I would agree with 451 Mopar as far as the lift change with the 1.6 rockers. his figures are corect. However I must disagree with him when it comes to duration. Changeing the rocker ratio will make the valve travel ferther. And it will have to move a little quicker to acomplish this task. However the actual amount of time and or degrees of valve lift will not be effected. Regardless of rocker ratio the cam grind remaines the same.Think about it the push rod doesn`t care what rocker you run, it just keeps doin the same thing all the time . And traveling the same distance it always has and always will with that same cam. Hope it helps. happy trails

[Dart]

From what I have seen the stock rockers are more like 1.42-1.45 to 1. They are not close to an actual 1.5.

If you have a cam that was advertised .509 for lift and you used the stock rockers here is how you would look for lift (advertised lift on a cam are all based on 1.5 to 1 ratio):

.509 / 1.5 = .3393 (lobe lift)

.3393 x 1.45 = .491 lift

or

.3393 x 1.6 = .543

[Dart]

One more thing: The static duation will change when you change the rocker ratio.

[451Mopar]

dirty dan, I think you mis-understoond me. The cams duration won't change, but because the valve opens quicker the engine may react as if the cam had a extra degree or so of duration.
For example, the valves will be "more" open durring the overlap period than with the lower ratio rocker arm. I don't think it is any real concern, it is just something to think about or factor if tring to put numbers into one of the dyno simulation programs.

[Olle B]

Hi
Minor diff in your calculations but one thing for sure!!!
I realy have to convince my old lady to buy new adjustable 1.6 rockers insted of my old 1.42!!??
The diff must be notable I guess!!
Maybe some extra HP compared to my old non adj worn out,,no prepreasured original 1.5!!
Thanks Olle B