Camshafts: What effect does increased lift have on performance?

[RustyRatRod]

LOL! I thought you were the square lobes guy. A lot goes into cam lobes and the spring pressures to control the motion. I never talk racing stuff, unless someone posts something real stupid. It does not interest me. I am a street guy that wants a fast car and only want to do it once, not have to dork with it for a long time and many, many miles. I don't care how an engine sounds as long as it will wind up and be fast. A race car is a completely different animal. What you are talking about is picking a lobe with the best area. The lobes are always a compromise.

That's cause over 90% of the guys here are talkin about their street cars and a select few talk about race stuff all the time for everything and think it's right for everything and it's not. I think their wives need bigger baseball bats.

 

[273]

Show us an example of head flow the same at .400 and .600. I swear, I'm gonna send your wife a new baseball bat cause she musta lost the last one.

Look at far left row, stock 318 head basically flows the same .350 -.700, even at .300 ain't too far off.

 

[RustyRatRod]

Look at far left row, stock 318 head basically flows the same .400-.700, even at .350 ain't too far off.
View attachment 1716355611

Yeah but my point is, using "his" theory, that stock 218 needs a .700 lift cam. duhhhhh LOL

 

[RustyRatRod]

Look at far left row, stock 318 head basically flows the same .400-.700, even at .350 ain't too far off.
View attachment 1716355611

......and thanks for posting that!

 

[273]

Yeah but my point is, using "his" theory, that stock 218 needs a .700 lift cam. duhhhhh LOL

Guess depends what your trying to accomplish But yes for most be little need to go past mid/high .400 lifts on that head.

 

[nitro_rat]

Lift: how much the valve is open.
Duration: how long the valve is open

A bigger lift with the same duration will open and close the valve faster which is harder on the valve train and cam lobe. It requires a greater spring pressure than a cam of equal duration and lesser lift.

Think about the valve like a door at the end of a hall way. If the intake port (hall way) can only accommodate a single file line and the door man opens and shuts the door all the way really fast maybe only one person can sprint through each time the door opens. But if one person only needs the door open half way to pass and the door man only opens the door half way but in the same amount of time as he swung it open all the way, maybe two or more people can walk through each time the door opens.

Additional lift only helps if the port behind the valve can support the additional flow. Generally speaking two cams with the same lift but differing durations, the longer duration will make more power. With the same duration and differing lift, the one with more lift will be peakier and work at higher RPM range.

It's a balancing act to get as much flow into the cylinder in the given amount of time. This is why roller cams make more power than an equivalent lift flat tappet cam. The roller can accommodate much faster opening and closing ramps so it can have more duration. Given the same duration, the roller will have the valve open longer because the ramps are faster.

Look at far left row, stock 318 head basically flows the same .400-.700, even at .350 ain't too far off.

That right there tells you that at .400 the port is flowing all it will flow. No point lifting past that (except to keep the nose of the lobe from being flat). Ramp the valve to .400 as quickly as practical, leave it open as long as possible, and close it as quickly as practical.

Pretend that these two lobes both flow the same volume of air for a given duration. Pretend the one on the left opens to .700 and the one on the right opens to .400. The one on the right is going to be much easier on the valve train than the one on the right, its going to require less spring pressure, and it's going to require less attention to clearances. Piston to valve clearance, coil bind, valve stem and seal height, etc.

 

[volaredon]

Now cam numbers make my head spin, so nothing but confuse me, especially when you dig deeper like overlap, dynamic CR, etc. lift and duration of and by themselves aren't as confusing... I often compare a stock 360-2 cam and a comp 252. Duration overlap etc are identical. And it ain't by much but lift is 0.410 on the stock cam and .425 on the comp. I wouldn't think you'd notice any difference at all between running either of these cams.
But, as lift becomes more radical with the same duration, is think the nanosecond that the valve is open for the greater amount on the higher lift, especially as rpms increase, isn't enough to mean squat as far as getting more garbage in, garbage out. In fact just the fact it would have to be moving faster to open farther in the same amount of time, it would just act like a fan and create turbulence. The 0.015 difference in my example above isn't enough of a difference I don't think to cause this.
But you talk about 0.050, maybe more, difference in lift at a given duration, yeah.

Another question does lift or duration play more of a part in how much vacuum a given engine makes

 

[273]

That right there tells you that at .400 the port is flowing all it will flow. No point lifting past that. Ramp the valve to .400 as quickly as practical, leave it open as long as possible, and close it as quickly as practical.

That's not true it's a about average flow. That head peaks at .350 but a .350 lift cam is gonna spend almost zero time at peak flow where as a .500 lift cam will be in max flow range (.350+) as soon as it as the opening ramp hits .350 until the closing ramp goes under .350, gonna spend more of it's duration above .350 (peak flow) which should mean more overall air flow.

View attachment 1716355618
Pretend that these two lobes both flow the same volume of air for a given duration. Pretend the one on the left opens to .700 and the one on the right opens to .400. The one on the right is going to be much easier on the valve train than the one on the right, its going to require less spring pressure, and it's going to require less attention to clearances. Piston to valve clearance, coil bind, valve stem and seal height, etc.

longevity is a separate issue and yes it would be a reason not to run crazy lifts but there is for power reasons to run more lift than where head flow peaks, now if you want to, that's a whole separate issue. Just like duration, more of it generally makes more power but there's reasons not too with that too.

If you could open and close the valve instantly you would only need to open to peak flow but we don't live in that world

 

[273]

Here's a pretty self evident pic, say head flows same peak flow from .450 to .550 which profile generally gonna move more air ?

Basically these cams are the same 0 to .200 the difference is .200+ where the head flows the most.

 

[nitro_rat]

That's not true it's a about average flow. That head peaks at .350 but a .350 lift cam is gonna spend almost zero time at peak flow where as a .500 lift cam will be in max flow range (.350+) as soon as it as the opening ramp hits .350 until the closing ramp goes under .350, gonna spend more of it's duration above .350 (peak flow) which should mean more overall air flow.

longevity is a separate issue and yes it would be a reason not to run crazy lifts but there is for power reasons to run more lift than where head flow peaks, now if you want to, that's a whole separate issue. Just like duration, more of it generally makes more power but there's reasons not too with that too.

If you could open and close the valve instantly you would only need to open to peak flow but we don't live in that world

My explanation was a gross oversimplification.

 

[318willrun]

It's cold out, so lets use a door letting in cold air for comparison.

• Lift - How far the door is opened. A door opened all the way quickly/shut quickly lets in a quick, cold blast.
• Duration - How long the door is opened. A door opened half of the way but held open for 30 seconds will drop the temp in the room even more having much more of an effect on dropping temps in the room.
• and Ahhhh... we keep leaving out what may be most important - the SIZE of the door !! If one is a pet door and one is a garage door, hmmmm...

 

[mopowers]

I think the take away is for cams with the same @.050" duration but with different lifts means the one with more lift will have steeper ramps, may require more spring pressure, and may be a little harder on the valve train but likely makes more power assuming the heads can support the higher lift.

The one with more lift likely has less .006" duration due to the steeper ramps, which would shut the intake valve sooner and build more cylinder pressure in theory too, right? Either way, I think the higher lift cams were developed to take advantage of the larger .904 Mopar lifters and generally result in more power. I'm no expert though and I've never even stayed at a Holiday Express.

 

[RustyRatRod]

Here's a pretty self evident pic, say head flows same peak flow from .450 to .550 which profile generally gonna move more air ?

Basically these cams are the same 0 to .200 the difference is .200+ where the head flows the most.

View attachment 1716355647

But then, we cannot look at "just" the camshaft lift to answer the question, since the engine is comprised of so many other variables. It's all combo dependent. Every bit of it.

 

[toolmanmike]

But the one with higher lift will spend more average time in the higher lift range then the lower lift cam and ports generally flow more at higher lifts.

Eg. low range 0-.250 higher range .251 - .500 which cam is gonna spend more average time at the higher lift range .500 vs .550 ?

It depends on the lobe design how fast it get's there and how long it stays in a particular lift range. Remember, for comparison, the duration doesn't change.

 

[1MeanA]

At some point there is diminishing returns plus your duration and overlap are going to increase.

 

[273]

But then, we cannot look at "just" the camshaft lift to answer the question, since the engine is comprised of so many other variables. It's all combo dependent. Every bit of it.

True, were just talking generalities. Obviously there more to it, but in general the cam with more lift is probably gonna make a bit more power. I'm sure you could find cases where it don't.

 

[Kern Dog]

I think the take away is for cams with the same @.050" duration but with different lifts means the one with more lift will have steeper ramps, may require more spring pressure, and may be a little harder on the valve train but likely makes more power assuming the heads can support the higher lift.

The one with more lift likely has less .006" duration due to the steeper ramps, which would shut the intake valve sooner and build more cylinder pressure in theory too, right? Either way, I think the higher lift cams were developed to take advantage of the larger .904 Mopar lifters and generally result in more power. I'm no expert though and I've never even stayed at a Holiday Express.

I am impressed with the knowledge shared in this thread, though I do get overwhelmed with some of it.
I've stayed at Holiday Inn Express' and found their name to be a lie. I slept at the same rate of speed as anywhere else.

Hughes seems to favor the more lift principle with this line of cams....

I mention them specifically because last Monday I tore down a 1990 360 with a Hughes cam in it. I have a thread here on the build.

The 360 build that has more turns than Willow Springs

I guess what I gathered from what I thought was this simple question was that higher lift on it's own opens and closes the valve faster and whatever advantage that offers is entirely dependent on the flow capabilities of the head.
Is that a simple and accurate interpretation?

 

[RustyRatRod]

I'm sure you could find cases where it don't.

Lots of them.

 

[RustyRatRod]

I am impressed with the knowledge shared in this thread, though I do get overwhelmed with some of it.
I've stayed at Holiday Inn Express' and found their name to be a lie. I slept at the same rate of speed as anywhere else.

Hughes seems to favor the more lift principle with this line of cams....

View attachment 1716355707

I mention them specifically because last Monday I tore down a 1990 360 with a Hughes cam in it. I have a thread here on the build.

The 360 build that has more turns than Willow Springs

I guess what I gathered from what I thought was this simple question was that higher lift on it's own opens and closes the valve faster and whatever advantage that offers is entirely dependent on the flow capabilities of the head.
Is that a simple and accurate interpretation?

Howards Cams have a lot of lift per duration, too. Just what a Chrysler needs to take advantage of the .903 lifter diameter. But then, other lobes work well, too.

 

[273]

I guess what I gathered from what I thought was this simple question was that higher lift on it's own opens and closes the valve faster and whatever advantage that offers is entirely dependent on the flow capabilities of the head.

Complete top end etc..

Is that a simple and accurate interpretation?

Pretty much.

 

[Newbomb Turk]

LOL! I thought you were the square lobes guy. A lot goes into cam lobes and the spring pressures to control the motion. I never talk racing stuff, unless someone posts something real stupid. It does not interest me. I am a street guy that wants a fast car and only want to do it once, not have to dork with it for a long time and many, many miles. I don't care how an engine sounds as long as it will wind up and be fast. A race car is a completely different animal. What you are talking about is picking a lobe with the best area. The lobes are always a compromise.

If it was 1980 I’d say I agree. It’s not 1980 any more.

Lift is our friend, whether it’s a street car or not.

 

[273]

It depends on the lobe design how fast it get's there and how long it stays in a particular lift range. Remember, for comparison, the duration doesn't change.

Yes there's a ton a variables but if you had to account for every possible variable in every discussion, you'd never be able to talk about anything. Some generalization are necessary to have a conversation.

I get duration don't change but durations at particular lifts do, with higher lift cams the cam is gonna spend more durations at higher lifts and generally that's a benefit.

It's quite obvious that the red and blue lobes is spending more of it's duration (time) at higher lifts then the black one, is it like for every cam that has more lift, no, is it always gonna translate to more flow, no, more power, no, (why I keep saying generally) but you should be able to see it can, all I'm saying.

 

[Newbomb Turk]

Yeah but my point is, using "his" theory, that stock 218 needs a .700 lift cam. duhhhhh LOL

That’s not what I said.

For a mild street engine in 2025 (I know this 21st century talk scares people) I can’t think of a single reason that .550 lift shouldn’t be the standard for lift.

That’s not a bunch of lift unless it’s 1980. Then it’s a lot of lift.

The biggest issue is getting the valve gear to take more lift.

I’d be running far more than .620 lift if I had better rocker gear. And that’s on a relatively mild 340 build.

Go back and look at say a 280 lobe from 1980 and then compare that to a modern 280 lobe.

On an older lobe you’ll see at .050 numbers from about 230-240.

The lobe I’m using is 282/255.

But what if I only need say 235 at .050???

In that same family of lobes I could drop down to 262 seat to seat. That’s HUGE.

If you drop down to an .842 lobe you’ll be you’ll need 287 to get to 254 at .050.

Back to my 255 example (I think I’m 281 seat to seat) so 281/255, to get that in an .842 lobe you’ll need to be 289/254.

Which cam will idle better and be more “streetable”? The one with less seat to seat duration.

The slow lobe is .550 lift and the fast lobe is .5994 lift.

Which cam will have better manners? Which cam will drive better?

Pretty simple really. Lift is great. Fast(er) lobes make better engines.

 

[RustyRatRod]

That’s not what I said.

For a mild street engine in 2025 (I know this 21st century talk scares people) I can’t think of a single reason that .550 lift shouldn’t be the standard for lift.

That’s not a bunch of lift unless it’s 1980. Then it’s a lot of lift.

The biggest issue is getting the valve gear to take more lift.

I’d be running far more than .620 lift if I had better rocker gear. And that’s on a relatively mild 340 build.

Go back and look at say a 280 lobe from 1980 and then compare that to a modern 280 lobe.

On an older lobe you’ll see at .050 numbers from about 230-240.

The lobe I’m using is 282/255.

But what if I only need say 235 at .050???

In that same family of lobes I could drop down to 262 seat to seat. That’s HUGE.

If you drop down to an .842 lobe you’ll be you’ll need 287 to get to 254 at .050.

Back to my 255 example (I think I’m 281 seat to seat) so 281/255, to get that in an .842 lobe you’ll need to be 289/254.

Which cam will idle better and be more “streetable”? The one with less seat to seat duration.

The slow lobe is .550 lift and the fast lobe is .5994 lift.

Which cam will have better manners? Which cam will drive better?

Pretty simple really. Lift is great. Fast(er) lobes make better engines.

Did 2 did 2. You said we need 600 lift and a 7AL ignition.

 

[Newbomb Turk]

Did 2 did 2. You said we need 600 lift and a 7AL ignition.

That should be the GOAL.