CAT3

iTrader: (9)

Ok, whats the difference between split cams that use a longer duration but shorter lift? Seems like you'd want the longer duration mated to the higher lift. I see some cams are 224/228 .580/.560 just an example...so what is that the duration does as compared to the lift.

Lift=how far the valve will open
duration= how long the valve will stay open.
me=confused!

Cal

iTrader: (1)

While both lift and duration can contribute to flow or area under the curve, duration has a greater affect on performance than lift since it has a bearing on valve overlap. I saw a '99 LS1 that put out over 400 rwhp with a 224/224 cam that had only a 0.533 lift.

niphilli

That is a good question. Maybe a cam guru can chime in and give you an answer.

The entire point of Lift and duration is go get as much air as possible into and out of the combustion chaimber. Lift accomplishes this by providing a larger opening to let air in/out and duration provides more time for the air to flow into/out of the chaimber. In theory with a cam that has more duration you need less lift to move the same volume of air.

So good question....What is the point of increasing duration while decreasing lift? Just to go easy on the valvetrain?

CAT3

iTrader: (9)

Niphilli, I really like your sig's pic. Schweet. Also, curious what does your name stand for?

ON TOPIC now, I am tryign to gain as much inside/in-depth/intimate knowledge of all this as I can because I am wanting to open my own shop in a few years, after I retire Uncle Sam. Little hodge-podge info like this really interests me. I though about the valvetrain issue as well, and as it does make sense, so does the poitn CAL is making about overlap, which leads to bleed off, and lower cyl pressure. I know I could pick up a book and read about all this, but I like to learn from different sources, sometimes a person can put into words a picture better than an editor.

TIA,
Charlie

niphilli

Hey Charlie- Thanks man

The name comes from the first two letters of my first name (Nick) and the first letters of my last name (Phillips). I was given this e-mail addy in Col. and it stuck. I am not that boring of a person though- I promise

TTT

CAT3

iTrader: (9)

ttt, up for debate, or general input....

soundengineer

iTrader: (16)

Try this link....Might be a little more than you need...but it will give a full explination...

http://howstuffworks.lycoszone.com/camshaft.htm

and typically the larger the #'s the more potential for horsepower ....above certain #'s and you will need some custom stuff done to your engine.

CAT3

iTrader: (9)

Nice link...didnt see the info for this question but theres a lot of good info. Thanks.

bryan c

once the valve lift reaches a certain height, the geometry of the intake/exhaust port limits any further flow, so it does no good to lift the valve any higher. this is why it is so important to match your cylinder heads to your camshaft. duration is a bit more complex, you want maximize volumetric efficiency (VE) over a desired rpm range. VE is just a measure of how well an engine functions as an airpump. The more air/fuel an engine cycles, the more work it can do, and the faster it does that work, the more power it makes. holding the valve open longer (more duration), generally shifts peak VE higher in the rpm range at the expense of reduced VE lower in the rpm range.

CAT3

iTrader: (9)

72Sub, So a 218/218 .590/.590 would have a lower peak than a 230/230 .560/.560? I thought that LSA was the resonsible for moving the power up or down the rpm band.

bryan c

LSA and duration are related by overlap. overlap occurs when the intake and exhaust valves are open at the same time. so in general, when you increase duration, you increase overlap. a tighter LSA also increases overlap, so you're correct, LSA also has a role in determining the power band. in a stock-head LS1, the 230/.560 would make more peak hp and at a higher rpm than the 218/.590, but would have some streetability issues.

nuzee

iTrader: (2)

Here is an oversimplified opinion of duration, lsa, & lift.

Duration (intake) dictates where the power peak occurs... the higher the duration, the higher the rpm at which peak power occurs. Because horsepower is a function of rpm, in general the greater the duration the greater the power.

LSA dictates the shape of the torque curve... the tighter the LSA, the peakier the curve, and vice versa, wider the LSA, the flatter the torque curve.

Note peaky torque curves produce less torque at both the low and high ends of the curve. That is why tight LSA cams can have a lousy off idle power and need to rev-up into its powerband in order to start shining.

Flatter torque curves from wide LSA cams adds to the low & high ends while triming torque in the middle. That is why you'll get a better pull off idle from a wide LSA cam. This is an important characteristic to have for A4s and not so much for M6s.

Ever notice a tight LSA cam quickly lose its pull after reving past its peak power, while wide LSA cams just seem to pull & pull & pull. That's been my experience.

Lift is, or at least was, usually limited by the cam lobe design. In days of yore, you needed a big lobe profile to build up high lift. This big profile meant large durations. So high lift and large duration went hand-in-hand. That's not a bad thing, at least they weren't being counterproductive to each other. Nowadays, with the aggressive cam lobe profiles, you can get more lift than your heads call for at a relatively low duration. So lift has become more "valve spring" limited.

nuzee

iTrader: (2)

CAT3
I edited my above post to remove my wisea$$ remarks. I was in a riled-up mood when I made the post, I apologize.

Cam talk can be very entertaining. I hope I didn't kill your thread.
nuzee

CAT3

iTrader: (9)

Your lucky I didnt see the remarks or I would've....

Anyway, this all seems to be such a finicky aspect. I have a xxxx lift but xxx dur, mine will better than the xxxxlift and xxx dur. etc..... Oh brother!

nuzee

iTrader: (2)

So you didn't see my remark about your mamma driving a Hyundai? Thank goodness! LOL j/k

Back to your original question....

The air flow dynamics is different during intake vs. exhaust. That has to affect why lift may be more influential on intake, while duration is more influential on exhaust.

Drew778

iTrader: (2)

:p

CAT3

iTrader: (9)

Right because of the thermal energy and how air movement is reactive toheat etc...got it...'

still seems to many choices and variables.

JeremyF

iTrader: (23)

There Is alot of good info here and I agree with alot of what was said.
theoretically a NA engine can only make a given amount of torque via VE now the max VE in a serious NA engine will be about 110% but usually what we are building here is in the range of 90-95%. That said the duration and LSA will determine where we will make pk HP&TQ as well as how broad the curve will be. The valve events of a larger duration (244/252 114 as opposed to a 216/220 114) cam will most definitely hurt lower rpm tq (VE). the smaller cam will have better velocity at lower engine speeds but will not be able to make the tq a lager cam will at the top of the RPM range.
The lift will only allow the cam to take advantage of the extra breathing by "lifting" more, given. But if it were left to any engine builder they would always take the right duration and less lift than viceversa.

jeremy Formato

lsx24

iTrader: (45)

I agree with the first part of the statement, but how true/accurate is the second paragraph quoted?

I always thought, for example, a TR224 112 lsa will give you more torque down low, but a slightly less top end; a TR224 114 lsa will give you a flatter torque curve, smaller torque peak, and reach a higher hp peak higher up in the band. Am I off base here?

I know for sure a 114 lsa will idle better and pass emissions easier than a 112 lsa, relatively speaking of course.

CAT3

iTrader: (9)

I think if you look at the curve like it is a rainbow the ends will produce lower amounts with a peakier cam...