If my stock cam is 207, 213 duration @.50 , at 415, 430 lift and LSA 117 then how can a different new cam with lower duration be much better than the stock one.

Sure the new cam will have more lift but is it the lift that would give you 30HP? If so then why not just add 1.6 rockers.

Anybody? Thanks.

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89Iroc, 305 TPI, WC T5, 3.08 Posi, Headers, Hooker Y-Pipe, 3 inch over the axle, Flowmaster 80, No Cat, Aluminium Driveshaft, Ported Plenum, Air Foil, K&N, All free mods,

 

Normally the higher the duration the higher the lift. For the simple reason that if you have to close a valve sooner then you can't open it as high.
Your cam has a real high lobe seperation so the exhaust valve closes before the intake opens, good for creating vacumn, smooth idle, fuel economy.

Most aftermarket cams will have a LS of 112
which is the optimun cam for performance, decent idle with good midrange torque and better top end.

Some you'll see with an LS of 108. This will give you even better mid range and top but now idle with suffer. Cams with longer duration usually will have less LS.
At 108 the exhaust valve hasn't closed all the way before the intake starts to open.
At midrange and topend the exiting exhaust gas helps to pull in the intake charge. But at idle the engine is not spinning fast enough to take advantage of the overlap so
when both valves are open you lose all your vacumn and causes an erratic (lopey) idle.

Yes 1.6 rockers increases lift and to a very slight degree it increases duration.

Whether your talking about lift, duration or lobe seperation what really matters is that it matches the heads. Easy enough but you also need to be concerned about the velocity of the air and not just amount of it, and that is not measured anywhere.

 

i'm no expert, i only pretend to be on here. as far as cams go when i want to understand something i usually look in my comp or lunati catalogs, they do a great job of telling how cams work. other than that i'll say a cam isn't about lift, duration, or LSA, but rather how they all work together. you're right if it was all about lift just run 1:6 rockers.

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

Think about the idea of "area under the curve"...

Imagine you have a 207°/213° cam made by someone who doesn't understand about or care about performance (like ahhhhh ... GM for instance and a stock L98 cam) so they don't bother to redesign their crappy grinds at the same time they re-invent the wheel (into a triangle) and dream up some stupid roller system that forces such radical changes in their product that the mfg costs are sky high. Now imagine you take all that foolishness and throw it in the trash and get a cam from someone else who has been making roller cams for decades and understands that you can open the valves faster and hold them open longer with a roller system than you can with a flat-tappet one. You'll probably end up with a cam that might have the same or less duration at .050", but might have 30° more duration at .100", 45° more duration at .200", etc.; and 15% higher overall lift. In short, even though that one duration number makes the 2 cams look like they aren't much different, in fact, they are like night and day.

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"So many Mustangs, so little time..."
ICON Motorsports

 

What the above post is explaining is the forgotten term of cam intensity, which is advertised duration-duration @.050" lift.

Say a cam with an advertised duration of 292 and a .050" duration of 234 and compare it with a cam with 285 advtised with the same .050 duration. The second cam will run better because the low end will be improved.

 

I smell calculus........

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1987 GTA L98 MD8
355, TFS Heads, LT4 Hot Cam
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