Let’s say you have two camshafts with identical specs except the lift.
Same duration, same intake centerline, same lobe separation but one has say .480 lift and the other has .520. What does the additional lift do for performance?
A quickie Google search has evolved (or DEvolved) into experimental AI which could be good or bad, but it stated that higher lift makes more power but primarily at high rpm. It stated that torque was often negatively affected while high rpm was increased.
That seems incorrect to me as that sounds more like the effect that duration has, not lift.
The old fashioned Mopar Performance camshafts always seemed long on duration and short on lift, I assumed it was because they figured that their stuff was intended to be used in Mopar engines utilizing the stock rocker arms and that once you get much past .500 lift, the rocker arms are at the limits in terms of contact patterns on the valve stems.
Hughes Engines looked at it the opposite way. Their cams are often long on lift compared to the duration numbers.
What are your thoughts?
The MP cams are designed in a certain parameter of thoughts which I find accurate in their description of balancing the track performance with still be streetable.
The key to this camshaft thinking is how the engine responds to the camshaft in making power and where you want to make the best and most power for your particular situation.
Duration allows more or less air and fuel into the cylinder with the cylinder head (only the cylinder head for this exercise) being the limiting factor.
Now for say, the cylinder head flows well to only .500 lift. More lift has the flow rate tank badly. Here, you don’t need more lift, so finding more power comes with duration. Holding the valve open longer allowing more air and fuel. But we know this raises the rpm level of performance and can be a draw back to the track being raced among many things.
Now! If the cylinder head flows really well to, let’s say .750. Lifting the valve up higher to get into the superior air flow characteristics of the cylinder head will allow more air and fuel to get in thus creating more power. Obviously.
Being that the duration hasn’t changed, the operating rpm range really doesn’t change much. It will rise some but the bulk of power remains the same in the same area but just with superior high end power being made. There should actually be an increase of power everywhere as in a broader and fatter power curve.
A slight loss of torque will happen. This has been seen before. Someone above wished for this test and it has happened before.
To continue my answer, I will also address the below quote:
But you cannot increase lift and have the same duration. Mathematically impossible. The extra lift increases the duration or you have an awkwardly weird ramp rate.
Not exactly true. The duration and lobe of the cams opening and closing points are not changed but what changes is the area under the curve gets fatter. The valve rises quicker and higher to stay within the opening & closing points. The cam lift becomes quicker which equals more aggressive.
A quicker opening valve almost always equals more power. There is a point that you can open the valve to quickly to take wastage of what it can/could offer. Mostly, it’s a intake track issue that won’t allow the air and fuel in generously quick enough to match the valve action.
This is also why you can see/read at the Hughes web site on how the intake track (intake manifold) should flow more than the cylinder head. IIRC, Hughes wrote something along the lines of greater than 15% better. Probably higher. I’d go higher if possible. (Often it is not.)
Ok, let’s go back to the cylinder head that kicks *** with great flow to .750 and beyond with an intake and carb set up, up to task.
Lift will directly effect HP.
Crap head and intake.
Lift doesn’t help anything. Will probably just simply hurt the engine and/or combo.
The old saying of you just can’t get THERE from HERE Iis due to the equivalent of everyone driving their car at 90 and maintaining speed as you neck down from an 6 la e interstate hwy to a one lane exit.
It’s just not happening. Everyone gets jammed up.
This is kind of where the low lift cams come into play very well. While I normally suggest getting as much lift as possible , sometimes this possible is limited to a stock head.
A stock 340/360 head flows around 210 cfm @ .520 lift on the intake.
(Just for argument sake)
Then simply get a cam that lifts the valve up to a maximum.500/.520, then hold it there for as long as possible (duration) to allow the most A&F to get in.
Most stock, as cast OEM heads, will flow well to about .500. In general, the valve job is responsible for lifts to 400-450 area. After that, look at the under valve area.
If you happen to have an old MP engines book, they don’t recommend a (bowl) ported head (340/360 engines) until you want to achieve ET’s in the lower 12 second range. The bowl ported head gets coupled with the MP mechanical cam, 284/.528.
This doesn’t mean you NEED a bowl ported head to run low 12’s, it’s just a better more efficient way rather than tax the head with more lift and/or using more duration with low lift.
I hope that wasn’t to confusing and answered your question.
