lift vs. duration
06-28-2002, 04:19 AM
#2
TECH Addict
Join Date: Dec 2001
Location: Fort Worth,TX
Posts: 2,340
Likes: 0
Received 0 Likes
on
0 Posts
Re: lift vs. duration </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 70 LS1:
<strong>For the same lift, what does more duration do?
For the same duration, what does more lift do?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I am not sure what your asking but I am going with .600/.600 lift on my next cam now I just have to figure out the duration part and lsa for my power band.
<strong>For the same lift, what does more duration do?
For the same duration, what does more lift do?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I am not sure what your asking but I am going with .600/.600 lift on my next cam now I just have to figure out the duration part and lsa for my power band.
06-28-2002, 08:55 AM
#3
Re: lift vs. duration </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 70 LS1:
<strong>For the same lift, what does more duration do?
For the same duration, what does more lift do?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Duration is the degrees of camshaft rotation that the valve is held off of the seat. If you have more duration while holding lift constant, then you're not opening the valve anymore than you were before. You're just holding it open longer.
If you hold duration constant and increase lift, then it's just the opposite. You're not holding the valve open any longer than you were before; you're just opening it more while the valve is off of the seat. Providing you use the stock 1.7 rockers for both comparisons and don't get your added lift from a set of higher ratio rockers (which will add a slight amount of duration, but not enough to notice), it will take a more aggressive lobe profile to open and close the valve at the exact same time as you did with the cam with lower lift.
<small>[ June 28, 2002, 08:59 AM: Message edited by: Trevor D ]</small>
<strong>For the same lift, what does more duration do?
For the same duration, what does more lift do?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Duration is the degrees of camshaft rotation that the valve is held off of the seat. If you have more duration while holding lift constant, then you're not opening the valve anymore than you were before. You're just holding it open longer.
If you hold duration constant and increase lift, then it's just the opposite. You're not holding the valve open any longer than you were before; you're just opening it more while the valve is off of the seat. Providing you use the stock 1.7 rockers for both comparisons and don't get your added lift from a set of higher ratio rockers (which will add a slight amount of duration, but not enough to notice), it will take a more aggressive lobe profile to open and close the valve at the exact same time as you did with the cam with lower lift.
<small>[ June 28, 2002, 08:59 AM: Message edited by: Trevor D ]</small>
__________________
06-28-2002, 02:14 PM
#5
Re: lift vs. duration Simplified answers:
Increasing lift and duration increase the power a motor can make. The realistic power potential potential from increasing lift is less than increasing duration.
Increasing lift has little negative impact on drivability, but it is harder on the valvetrain. Increasing lift is limited by the piston to valve clearance.
Increasing duration creates more power, but drivability is eventually diminished and emissions increase. Increasing duration tends to shift the power band up into the higher rpm range too.
Increasing lift and duration increase the power a motor can make. The realistic power potential potential from increasing lift is less than increasing duration.
Increasing lift has little negative impact on drivability, but it is harder on the valvetrain. Increasing lift is limited by the piston to valve clearance.
Increasing duration creates more power, but drivability is eventually diminished and emissions increase. Increasing duration tends to shift the power band up into the higher rpm range too.
