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Check out the attached, very professional :), hand-drawn torque curve. The area that I drew a red box around represents the area that switches from a convex curve to a concave curve before the peak torque. The bigger the cam, the more pronounced this effect becomes. Can anyone explain why big cams do this to the torque curve?

I'm guessing that's where the scavenging starts pulling more air in, which causes the torque to suddenly increase very aggressively. Then, even with the scavenging, it finally peaks out and starts falling away.



Here are some examples:

http://www.ls2gto.com/forums/showpost.php?p=1690980&postcount=6
http://www.ls2gto.com/forums/showpost.php?p=1631588&postcount=3
http://www.ls2gto.com/forums/attachment.php?attachmentid=33895&d=1146084092
http://www.ls2gto.com/forums/showpost.php?p=1456626&postcount=1

It's hard to see on this one because of the scale of the graph
http://www.ls2gto.com/forums/showpost.php?p=1750037&postcount=7
 

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looks like the transition area where engine rpm and intake demand overcome the negative pressure in the intake manifold caused by the overlap designed into the cam profile. as the rpms increase, the intake velocity and pressure match, then exceed the blowback...
 

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3,381 Posts
CycloneGTO said:
Check out the attached, very professional :), hand-drawn torque curve. The area that I drew a red box around represents the area that switches from a convex curve to a concave curve before the peak torque. The bigger the cam, the more pronounced this effect becomes. Can anyone explain why big cams do this to the torque curve?

I'm guessing that's where the scavenging starts pulling more air in, which causes the torque to suddenly increase very aggressively. Then, even with the scavenging, it finally peaks out and starts falling away.



Here are some examples:

http://www.ls2gto.com/forums/showpost.php?p=1690980&postcount=6
http://www.ls2gto.com/forums/showpost.php?p=1631588&postcount=3
http://www.ls2gto.com/forums/attachment.php?attachmentid=33895&d=1146084092
http://www.ls2gto.com/forums/showpost.php?p=1456626&postcount=1

It's hard to see on this one because of the scale of the graph
http://www.ls2gto.com/forums/showpost.php?p=1750037&postcount=7
I think you are correct in your assumptions. ( that last one is mine) I know when I hit 4 grand, it amost feels like nitrous has come on. It will actually break the tires loose at that point sometimes. I know with higher compression, and better flowing heads, this curve is much flatter. I know that at 6500 I run out of air. My stock intake can jsut not keep up. I know others will the same setup as myself running the fast 90 do not have the problem I have.
 

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Discussion Starter #4
Thanks guys
 
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