Indepth Info on Overlap
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From: Lake Anna, VA/ Fairmont, WV
Indepth Info on Overlap I'm hoping some of my questions can be cleared up by a few of our Tech experts.
For example my current cam in my 360ci Marine SBC is a Hyd flat Tappet
.50 224/224 .465/.465 114 LSA 109ICL IVO 3 IVC 41 EVO 51 EVC -7
.006 282/282 IVO 32 IVC 70 EVO 80 EVC 22 119 Exhaust Centerline
Overlap .006 = 54 .050 = -4
Makes good power but has a very low 7.41-1 DCR.
A Marine SBC needs to idle 700-850 rpms max as anything more will tear up the gears in the outdrive. Hence we are cam limited and proper selection is vital. I'm going for a different cam with similar specs but a much better DCR and more lift.
.50 219/227 .468/.489 112 LSA 108ICL IVO 1.5 IVC 37.5 EVO 49.5 EVC -2.5
.006 262/268 IVO 23 IVC 59 EVO 70 EVC 18 116 Exhaust Centerline
Overlap .006 = 41 .050 = -1
This cam has a 8.05-1 DCR and less overlap at .006 but more at .050.
In my research i've found that less overlap makes for better idle and vaccum but hinders WOT top end performance. And the same goes if you reverse it, more overlap promotes WOT top end performance but hinders idle, vaccum and low end performance.
What is the relation of overlap between .006 and .050? Which of the two is more important to focus on? Thanks guys for the help.
For example my current cam in my 360ci Marine SBC is a Hyd flat Tappet
.50 224/224 .465/.465 114 LSA 109ICL IVO 3 IVC 41 EVO 51 EVC -7
.006 282/282 IVO 32 IVC 70 EVO 80 EVC 22 119 Exhaust Centerline
Overlap .006 = 54 .050 = -4
Makes good power but has a very low 7.41-1 DCR.
A Marine SBC needs to idle 700-850 rpms max as anything more will tear up the gears in the outdrive. Hence we are cam limited and proper selection is vital. I'm going for a different cam with similar specs but a much better DCR and more lift.
.50 219/227 .468/.489 112 LSA 108ICL IVO 1.5 IVC 37.5 EVO 49.5 EVC -2.5
.006 262/268 IVO 23 IVC 59 EVO 70 EVC 18 116 Exhaust Centerline
Overlap .006 = 41 .050 = -1
This cam has a 8.05-1 DCR and less overlap at .006 but more at .050.
In my research i've found that less overlap makes for better idle and vaccum but hinders WOT top end performance. And the same goes if you reverse it, more overlap promotes WOT top end performance but hinders idle, vaccum and low end performance.
What is the relation of overlap between .006 and .050? Which of the two is more important to focus on? Thanks guys for the help.
Teching In
Joined: Aug 2005
Posts: 26
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Not all profiles are the same. So, it basically depends on your profiles. I would say the .006 is the more important value, .050 is just some standard everyone uses to compare cams with. The .006 value is when the valves are considered open. When they're opening and closing is what gives your engine its personality. OEM seldomly uses .050 values.
Yeah what you need to worry about is the overlap area in sq in degs and even then a more aggressive lobe will make a larger effect on overlap and power. Then again the valvejob can have a ton to do with it as well.
Bret
Bret
