six cams- how would they perform in an ls1 stock shortblock with ls6 intake, lts and ory and tune? (not my specs just for sake of comparison)

advertised 260/260 @.50 216/216 .200 lift 133 -Isky lobes
advertised 266/266 @.50 216/216 .200 lift 141 -comp xfi high lift
advertised 269/269 @.50 216/216 .200 lift 135 -comp xer lobe
advertised 270/270 @.50 216/216 .200 lift 130 -comp xer low lift
advertised 277/277 @.50 216/216 .200 lift 139 -crane
advertised 278/278 @.50 216/216 .200 lift 133 -crane




notice they all have the same duration @.50 and this is the reason for the question. How will cam that has the same durations @.50 compare when there is a 6-18 difference in the advertised durations assuming everything else equal as much as can be so (same lift, lsa)? Will the cam with the larger advertised duration have more/ less rpm?, make more/ less power?, better/ worse average (under the curve) power?, more torque/ less torque etc.

I would like this to be a concentrated discussion and assume that the IVC closing is the same for the above cams same lsa but diff adv/retard to keep the IVC the same/close. Also don't mention if you prefer single/dual reverse pattern cams etc. to be clear: THIS IS NOT A "PLEASE HELP ME PICK A CAM" THREAD!!!!! THESE ARE NOT THE SPECS I AM THINKING OF USING AND I DONT WANT RECOMMENDATIONS. please DONT post your cam suggestions on what to buy or what works well etc. I am looking for specific advice as mentioned above.

 

There is a good thread about this on the front page of this section, IIRC; however, it's part of off-topic discussion in the thread, IIRC. I'll look for it...

EDIT: Shoot. Couldn't find it. Pred-Z talks about ramp rates, which is the heart of the answer to your question. I'll PM him in a few hours.

 

Thanks. I can tell by the specs that some of the lobes come off the seat faster than others and have more duration @ .200. The going belief is that the faster ramps will provide more power under the curve etc and that the cam will act bigger etc. but how much will a 260/260 216/216 have a similar peak, rpm range etc as a 278/278 216/216 same lsa and ivc ( i know the valve events would still be different and so comparing these extremes is tricky but I am going for root cause here)- I would say no myself but truth be told I'd like to get intto the finer points of why it will or why it will not.

 

To understand this fully you'll need to read on cam dynamics first.
Then in the sticky section there are 2 or 3 previous threads about "cfm requirement by rpm" and cam discussion 1 & 2
You'll find a lot of info in there.

From durations at various lift you can get an idea of the ramp rate (sharpness of profile) of the lobe itself.
Exemple:
.006 Duration - .050 Duration = variance rate

This variance rate can be used as a "yardstick" to get an idea of the lobe agressiveness.

advertised 260/260 @.50 216/216 .200 lift 133 -Isky lobes > Variance= 44
advertised 266/266 @.50 216/216 .200 lift 141 -comp xfi high lift> Variance= 50
advertised 269/269 @.50 216/216 .200 lift 135 -comp xe lobe> Variance = 53
advertised 270/270 @.50 216/216 .200 lift 130 -comp xe low lift >Variance = 54
advertised 277/277 @.50 216/216 .200 lift 139 -crane > Variance = 61
advertised 278/278 @.50 216/216 .200 lift 133 -crane > Variance = 62

there is also XE-R lobes that have a variance of 49 (other 2 above are usually known as XE)

So from the data above you then can pretty much categorize the lobe agressiveness as follow: (the smaller the variance = the more agressive)

Isky being the most agressive
Comp XE-R next
Comp XFI next
Comp XE HL next
Comp XE LL next
Crane 1
Crane 2


Now I cannot verify Isky and Crane because I do not know if those .006, .050 values are correct. I am actualy looking at Isky lobes and i'm awaiting some data on these. As for Crane they usualy advertise at .040 not .050 so I am unsure of above.

Now to briefly brush on the rest:

How the cam behaves in the band is mainly interpreted by it's valve events IVO/IVC/EVO/EVC, Those valve events at different lifts will give you the picture of how the cam is behaving or if you rather say dictating the motor its valve events during its 4 stroke cycle.
Added to that is lift.

so now you have how long a valve will open/close (duration) + where it happens in the stroke (valve events) + how far the valves open (lifts), put all these together (in the 4 stroke cycle) and NOW you get the picture of how the powerband is behaving.

Of course all of that is relative to the parameters of that 4 stroke unit and that involves induction cfm (from air intake to heads) and Exhaust cfm (heads to headers etc...), pump in/pump out (Overlap plays a part in here) as well as size of motor, stroke Vs bore etc..

So how does one interprets all of these to find the sweet spot in a cam for a said application?

Besides knowledge of said dynamics/physics, part of it is experience and data collection from actual testings.

I tried to make this as Lehman as possible for this is a deep subject and I merely touched the surface.
Also while there are founded theories about cam design, there are also different philosophies.
Sometimes when the improbable (as nuts as it seems on paper) works in a certain environment, one can only deduct that this is then definitely probable.
This is where a lot of "philosophies " emerge and why different poeple will tend to spec cams differently.
Bottom line, as per my experience, if it works, use it; no matter how ludicrous it may seem to some of main stream thinkers. A certain form of "out of box" thinking if you wish....

 

And, you did a wonderful job. Thanks, Predator!

 

You need lobe lift in there as well.