I see some cams in online catalogues, some have identical advertised figures, but diffrent @50 ratings. why ?

crane HR-276-2S-12 IG

ADV Duration
Intake 276 °
Exhaust 284 °
Duration
Intake 214 °
Exhaust 222 °

Compcams XR276HR

ADV Duration
Intake 276 °
Exhaust 282 °
Duration
Intake 224 °
Exhaust 230°

Lunaty 01-HR7-HR8-12-A01

ADV Duration
Intake 276 °
Exhaust 284 °
Duration
Intake 210 °
Exhaust 218°

What does one have that the other doesnt ?

better technology ?
more accurate engineering ?

Thanks

 

They are measured at a different lift point reference.

Crane is typically .004 .0042 or .0045"
Comp cams typically .006"

 

So, does that make one brands specs more advanced or
acurate then an other?

 

It also means the lobe lift is more radical (ie. better manners yet more cam for hp) it lifts the valve quicker. That is when the adv. is small and the @ .050 is greater.

 

Ok, I'm bored and it's late....

To expand on what has already been mentioned:

Since no cam company has agreed on a point from which to measure the advertised or seat to seat duration, they agreed on a .050" of tappet lift as a general referance point.

Like DD said, the smaller the gap between the 2 numbers (advertised and seat to seat), the quicker the ramp rates, or rate at which the valve opens. It doesn't have THAT much to do with lift, as the ramp can turn to the nose at any given point for the most part.

Generally, comparing cams, I start by looking at the .050" duration (and lift). Because every cam grinder measures the advertised at different places, you really can't get an adequate feeling for comparison. Comparing the .050" duration and the lift gives a general feel for its aggressiveness. Then I look at the advertised. That tells me how fast/slow the ramp rates are. Case in point: compare an edelbrock cam to a Comp Xtreme Energy of similar duration @ .050". Once I've done all that, I generalize and get a basic idea for what the lobe action is. For example: A cam with small duration figures but lots of lift may seem decieving (oh, lots of lift, thats good) but then you calculate the ramp rates and get an idea for the nose shape and you see that there really isnt THAT much time spent at the higher lifts. I.e. not much time for air to flow on the top end of the lobe, where it REALLY flows. The inverse is also true. A cam with more duration, but not as much lift will spend more time at higher lifts permitting more air to pass per given duration. That's a glimpse of what I look at when I look at cams. Area under the curve....so to speak...

 

Interesting, Ill keep reading on the subject.


Thanks

 

Not to long ago i saw a lunati hydro roller with 234/242 duration but only .505/.515 lift....

a HotCam (since the lift is comparable) is a 218/228 duration...

a GM 847 (since the duration is comparable) is .56x/.572 lift...


i think that lunati cam would runs its *** off

 

What? Cams are like women, there are millions of them and they still can't do a proper job. Thats why they need to make many different designs.

But seriously i'm an idiot. There are many different varibles to consider when considering a cam, lift, .05" duration, and seat duration. All have a specific purpose and need, it is best to consultate a cam expert when dealing with them.

 

Between all the various people here, I'm sure we've got the essentials pretty much under control

 

No but they'd like you to think so.

All the companies make fast-action asymetrical lobes.
They are actually more alike then different in their aproach but the advertized numbers are measured differently.

You have to actually measure both cams to tell them apart. (using a common lift reference)
Keep in mind that a running engine is a very dynamic thing. There is a lot more to a sucessfull cam lobe design then the difference between the advertized duration and .050" durations.

Cams that push the limits of lobe design like Comp's Extreme Energy series require stronger springs to avoid premature valve float and tend to wear out quicker by the meer fact of requiring more spring pressure to control the more intense valve action.

Generally, a high(er) lift cam will wear the valve train quicker too.

As stated above the shape of the lobe is more important than the peak lift numbers.
There is no free lunch.

 

Intriguing .. Tho will the manifacturers give you a graph
illustration the shape of the lobe ?

Other that Isky, havent seen any other (yet) ..

Thanks for all the info guys !

 

The timing card is your friend. If you cannot find one, request one. On the outside, it may just look like measured specs and figures. But, if you read between the lines, there is all the data you need to make an accurate judgement on whether or not the cam is right for you.

As far as manufacturers giving out lobe designs, doubt it. Cam companies print out the blantantly obvious stuff on a piece of paper and hand it off as the timing card. With knowing what the seat measuring point is for the given manufacturer, using the seat duration, .050" duration, and lift, along with the general type of cam (flat tappet, roller, hydraulic or solid) you can get a pretty good idea of what the lobe will look like.

To F-BIRD's comment about higher lifts and valve train life, I would like to add the quicker ramp rates to that equation. Quicker ramp rates throw the valve open quicker (And close it faster) so the spring compresses and decompresses at a higher rate.

These 2 pictures off Holley-Lunati's site that I like to reference to in regards to area under the curve:

 

Cool, thanks Stekman