I know this may sound stupid to some of you, but what are the differences between a high and low lift cam of the same duration and LSA? Does the power band shift or lose low end torque to gain high end power or vice versa? Could someone please clarify this for me. Thanks

 

The high lift cam will have more duration at a higher lift,meaning a much more aggressive lobe profile.The high lift cam will make more power,at the expense of idle quality and valvetrain stress.You'll need to upgrade the valvetrain to cope with the higher lift and you'll need to do more tuning to make the truck idle and run properly at part throttle.

 

Not right on the idle quality statements.

With a more aggressive lobe, the valve stays shut just a bit longer (less overlap), then snaps the valve open quicker, then comes to a higher peak usually. This creates less overlap below .050 lift which improves idle quality. It then opens the valves more above .050 which improves power gains. This slightly more drastic valve action does create more stress and requires better springs. It will also have a bit more valvetrain noise.

 

if you mean the same durration at .004 and higher lift then you will have steeper ramps. more power overall, depending on the springs, lifters, pushrods and valves- and how radical you go- they could all see decreased life expectancies.

If its the same durration at .050 then you will have a longer durration at .004

 

A more aggressive can sometimes give a better idle,but that depends on how the grinder designs their ramps,a better indication of idle quality might be to compair the difference of advertised duration and lobe separation.Duration measured at.050"gives a good comparison of cams from different manufacturers,but compairing advertised or gross duration will give a better indication of performance and idle charicteristics between 2 cams from the same manufacturer.You can also calculate overlap from advertised duration.To say the aggressive lobe will idle better may not be correct,do you homework.A phone call to the grinder will also yeild a lot of information.

 

He means .050 lift.

That’s a very ambiguous statement and not correct no matter what it means.

Take a look at the lift numbers for these two comp 212/218 cams:

XE
intake
.004 - 265
.050 - 212
.200 - 126

exhaust
.004 - 271
.050 - 218
.200 - 132


XE high lift
intake
.004 - 265
.050 - 212
.200 - 131

exhaust
.004 - 271
.050 - 218
.200 - 136


Both these cams have the same .004 and .050 lift durations. Only after .050 does the high lift cam ramp up faster. That is a function of the lobes. If the XE-R lobe were displayed here, then its .004 numbers would be smaller than the same .050 duration XE or XE-high lift cam.

To give an accurate answer to the original question, we need the exact lobes, LSA, duration and advance. If not, its all just "in general" type answers. But to give it a stab, the powerband should be longer with a more aggressive lobe since it allows more air mix to enter. Low end should be comparable, but this does depend on all the complete cam specs.

 

It the exact cams you were talking about BigTex. The 212/218 comp XR265HR low and high lift.