How do you choose a lobe that gives the requisite seat to seat duration (as per some calculator) that's as "fast" as is reasonable possible while still providing for some degree of durability?
Let's say an open road event engine (at least once in a while) and cross country driver. And lots of drag racing.
I can't say I've had any kind of longevity issues with something along the likes of Comp's 288/294, 236/242, .347/.360 lobe (and 1.6 rockers) but I can't say the 274/282, 224/230, .359/.356 did me any favours. Comps XFI profile.
Target is a 6500 RPM shift. Peak HP at or around 6300.
FWIW, the valvetrain has proven reliable enough with those cams, RPMs and mileage.
What's a reasonable split for that specification?
Cam Duration: Adv. vs .050
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Stan Weiss
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Re: Cam Duration: Adv. vs .050
Looking at these 2 lobes in average inch degrees.
► 0.050 /((288-236)/2) = 0.0019230769230769232
► (0.347-0.050)/(236/2) = 0.0025169491525423729
► 0.050/((274-224)/2) = 0.002
► (.359-0.050)/(224/2) = 0.0027589285714285715
► 0.0027589285714285715 / 0.0025169491525423729 = 1.0961399711399711 - From 0.050" to max lift the 274 is an average of 109.6% fast
► 0.002 / 0.0019230769230769232 = 1.04 - From seat to 0.050" the 274 is an average of 104% faster
With looking at 0.200" numbers for each lobe we might see even a great difference.
Stan
► 0.050 /((288-236)/2) = 0.0019230769230769232
► (0.347-0.050)/(236/2) = 0.0025169491525423729
► 0.050/((274-224)/2) = 0.002
► (.359-0.050)/(224/2) = 0.0027589285714285715
► 0.0027589285714285715 / 0.0025169491525423729 = 1.0961399711399711 - From 0.050" to max lift the 274 is an average of 109.6% fast
► 0.002 / 0.0019230769230769232 = 1.04 - From seat to 0.050" the 274 is an average of 104% faster
With looking at 0.200" numbers for each lobe we might see even a great difference.
Stan
Stan Weiss/World Wide Enterprises
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
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Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
Re: Cam Duration: Adv. vs .050
I appreciate the data Stan. Thanks.
From the way I see it, and based on the way those two particular cams ran, (in a general sense, not power output), that additional 10% of intensity might represent the tipping point between maximizing performance and ensuring durability.
The XFI lobes have always been touted as aggressive but I suppose that's relative. That said, while I don't believe I had any issues with valvetrain control with them, they were noisy when compared to the Xtreme Energy profile. That noise to me might be cause for a longevity concern.
How would an "endurance" lobe compare to something more drag race/short blast interval orientated?
FWIW: This is a hydraulic roller application. Comps short travel version. Also Crower full roller 1.6 ratio rockers.
From the way I see it, and based on the way those two particular cams ran, (in a general sense, not power output), that additional 10% of intensity might represent the tipping point between maximizing performance and ensuring durability.
The XFI lobes have always been touted as aggressive but I suppose that's relative. That said, while I don't believe I had any issues with valvetrain control with them, they were noisy when compared to the Xtreme Energy profile. That noise to me might be cause for a longevity concern.
How would an "endurance" lobe compare to something more drag race/short blast interval orientated?
FWIW: This is a hydraulic roller application. Comps short travel version. Also Crower full roller 1.6 ratio rockers.
Kevin
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David Redszus
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Re: Cam Duration: Adv. vs .050
Here is a quick and simple approximation of cam angle area for hydraulic lifter cams.
Index =10 + [duration (deg) x lift (in)]
Does not work very well for cams with CV ramps.
Index =10 + [duration (deg) x lift (in)]
Does not work very well for cams with CV ramps.
Re: Cam Duration: Adv. vs .050
Mike Jones
Jones Cam Designs
Denver, NC
jonescams@bellsouth.net
http://www.jonescams.com
Jones Cam Designs' HotPass Vendors Forum: viewforum.php?f=44
(704)489-2449
Jones Cam Designs
Denver, NC
jonescams@bellsouth.net
http://www.jonescams.com
Jones Cam Designs' HotPass Vendors Forum: viewforum.php?f=44
(704)489-2449
Re: Cam Duration: Adv. vs .050
I appreciate all of the replies gentlemen. I'd read your Harvey Crane post before Mike. Very informative.
Intensity and aggresiveness are the attributes that I'm referring to but what I'm asking is where is the line drawn between a lobe that'll survive miles of WOT (as in an open road event) and something that has more of a drag race flavour.
I may take David's Index math and build a spread sheet of some likely candidates and present that to the crew here.
I'm willing to give in on the maximum output effort (as that was the plan for a drag only car) and accept something that might be a little kinder to all the parts involved.
Thanks again.
Intensity and aggresiveness are the attributes that I'm referring to but what I'm asking is where is the line drawn between a lobe that'll survive miles of WOT (as in an open road event) and something that has more of a drag race flavour.
I may take David's Index math and build a spread sheet of some likely candidates and present that to the crew here.
I'm willing to give in on the maximum output effort (as that was the plan for a drag only car) and accept something that might be a little kinder to all the parts involved.
Thanks again.
Kevin