Is duration @.050 or Lift more important ?

[Mike Gaines]

Someone educate us all.... is duration @.050 more important TO DRAG RACE PERFORMANCE or Lift ? For example my cam is 273Int & 283Exh @.050 and my lift is right at .600 plus my 1.6 rockers. How does that stack up to a cam with basically the same duration but .700 Lift ?

 

[Hemirunner]

This is a gross oversimplification but lift will mainly be determined by application, cam type, and where the port stalls. Duration will change the engine characteristics far more than lift and it is determined by a whole host of factors including minimum CSA, static compression, cubic inches, etc, etc. If the two cams are the same duration, the one with .700 lift will have a greater acceleration rate of the lifter up the ramp and open. ie, more aggressive lobe profile.

 

[lewtot184]

same duration with more lift will give more area under the curve. noticeable at lobe lifts above .200" but not much difference, if any, at .050". .050" numbers to me are only a piece of the action. to better know the lobe you need seat, .050" and .200" numbers. better yet, map the curve out with a degree wheel.

 

[Mike Gaines]

This is a gross oversimplification but lift will mainly be determined by application, cam type, and where the port stalls. Duration will change the engine characteristics far more than lift and it is determined by a whole host of factors including minimum CSA, static compression, cubic inches, etc, etc. If the two cams are the same duration, the one with .700 lift will have a greater acceleration rate of the lifter up the ramp and open. ie, more aggressive lobe profile.

But....my question is: will the cam with same duration but more lift be quicker in the quarter mile?

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same duration with more lift will give more area under the curve. noticeable at lobe lifts above .200" but not much difference, if any, at .050". .050" numbers to me are only a piece of the action. to better know the lobe you need seat, .050" and .200" numbers. better yet, map the curve out with a degree wheel.

Thanks for the insight, but my question still is: is the cam with same duration but higher lift quicker in the quarter mile? I'm presuming that would be, of course.

 

[rumblefish360]

In a nut shell, I'll try to re explain or clear up the answers above.
Again, in a case of over simplification:

Same exact cams except one has a .600 lift and the other a .700 lift on a engine/car set up that can handle each cam lift. The larger lifting cam should be faster.

But this is a major over simplified answer. And for this discussion, to many factors are missing to really show the possible bennifit of ether cam.

Lewtot184, idea of measuring with a degree wheel is a little bit of a difficult thing to do, it will take a while to perform, but the resulting graph would help show the area under curve pretty well. It would be seen even with a swap of rocker arm ratios.

Remember that the most smallest change is a huge issue in an engine.

 

[lewtot184]

bigger doesn't always mean more. it's a package deal.

 

[rumblefish360]

Exactly. Installing a bigger cam doesn't automatically mean you'll go faster.

 

[dvw]

You start with a given cubic inch and how many rpm you want to run it to. That will give you the air flow needed through the intake tract. Once that is known the duration is selected for the desired rpm. Not enough duration will not allow enough time to fill the cylinder at the desired rpm. If the intake tract flow numbers are lower than desired then additional lift may help crutch it. All inline valve motors will reach a rpm where they are intake valve diameter limited. A larger cam can crutch a inefficient/small intake port to a point. Seldom will a given duration give you less than desired lift do to the limitations in tappet acceleration. Lift will seldom hurt power. So that being said if your duration is correct for your application and you have an intake that is less than optimal (most of us) than lift should make more power.
Doug

 

[383man]

You start with a given cubic inch and how many rpm you want to run it to. That will give you the air flow needed through the intake tract. Once that is known the duration is selected for the desired rpm. Not enough duration will not allow enough time to fill the cylinder at the desired rpm. If the intake tract flow numbers are lower than desired then additional lift may help crutch it. All inline valve motors will reach a rpm where they are intake valve diameter limited. A larger cam can crutch a inefficient/small intake port to a point. Seldom will a given duration give you less than desired lift do to the limitations in tappet acceleration. Lift will seldom hurt power. So that being said if your duration is correct for your application and you have an intake that is less than optimal (most of us) than lift should make more power.
Doug

I agree and well sad. Ron

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bigger doesn't always mean more. it's a package deal.

I also agree with this. Hey at least I found something we agree on. Lol. Ron