In depth- LSA explained
02-27-2017, 04:32 AM
#11
Gold Member
Gold MemberThread Starter
Lobe separation angle, is simply the result of valve timing events.
The engine does not know the difference between a 108, and a 114 LSA. It only sees the result of when the valves are opening, and closing. That changes, with duration, intake centerlines, exhaust centerlines, and so on.
A cam with a 114 LSA, may have a 110ICL. Also referred to as, 4* of advance built in. A cam with 108 LSA, might have an ICL, of 106*, or 2 deg of advance built in. What changes, is the valves opening and closing points, assuming duration hasn't changed.
As stated, overlap, is what matters. 114 LSA, doesn't mean you'll have less overlap, than a different cam, that has a 110 LSA.
A good example, would be, the HP500 cam, vs the 525 EFI cam. The HP500 cam, has 110 LSA, and 525 EFI cam, has 114 LSA. However, OVERLAP,
HP500=5* overlap
525EFI = 12* overlap
The HP500 cam, is a 222/230 110 LSA. The 525 EFI cam, is 236/244 114 LSA.
The engine does not know the difference between a 108, and a 114 LSA. It only sees the result of when the valves are opening, and closing. That changes, with duration, intake centerlines, exhaust centerlines, and so on.
A cam with a 114 LSA, may have a 110ICL. Also referred to as, 4* of advance built in. A cam with 108 LSA, might have an ICL, of 106*, or 2 deg of advance built in. What changes, is the valves opening and closing points, assuming duration hasn't changed.
As stated, overlap, is what matters. 114 LSA, doesn't mean you'll have less overlap, than a different cam, that has a 110 LSA.
A good example, would be, the HP500 cam, vs the 525 EFI cam. The HP500 cam, has 110 LSA, and 525 EFI cam, has 114 LSA. However, OVERLAP,
HP500=5* overlap
525EFI = 12* overlap
The HP500 cam, is a 222/230 110 LSA. The 525 EFI cam, is 236/244 114 LSA.
Comp cams guy states in the piece "a cam with a tighter LSA is always going to have more overlap" which according to your example just isn't true. In the end I guess it would have been nice to see the cam cards for all three to get the full story.
02-27-2017, 05:30 AM
#12
Registered
iTrader: (1)
Adding duration also adds overlap, changes opening and closing points, and etc,etc.
CC was comparing identical specs other than different LSA's...so their statement was true for what they did.
02-27-2017, 06:24 AM
#13
Registered
iTrader: (3)
Right. If the duration is the same, then yes, it will increase overlap over the same exact cam, with a wider LSA.
Like the 525EFI cam, and the 741 cam. same durations, but 525 is 114. Overlap is 12 on the 525 cam, and 16 on the 741. They also make it with a 110 lsa, and that has 20* of overlap. AT .050 of course.
Like the 525EFI cam, and the 741 cam. same durations, but 525 is 114. Overlap is 12 on the 525 cam, and 16 on the 741. They also make it with a 110 lsa, and that has 20* of overlap. AT .050 of course.
03-02-2017, 03:12 PM
#14
Platinum Member
Lobe separation angle, is simply the result of valve timing events.
The engine does not know the difference between a 108, and a 114 LSA. It only sees the result of when the valves are opening, and closing. That changes, with duration, intake centerlines, exhaust centerlines, and so on.
A cam with a 114 LSA, may have a 110ICL. Also referred to as, 4* of advance built in. A cam with 108 LSA, might have an ICL, of 106*, or 2 deg of advance built in. What changes, is the valves opening and closing points, assuming duration hasn't changed.
As stated, overlap, is what matters. 114 LSA, doesn't mean you'll have less overlap, than a different cam, that has a 110 LSA.
A good example, would be, the HP500 cam, vs the 525 EFI cam. The HP500 cam, has 110 LSA, and 525 EFI cam, has 114 LSA. However, OVERLAP,
HP500=5* overlap
525EFI = 12* overlap
The HP500 cam, is a 222/230 110 LSA. The 525 EFI cam, is 236/244 114 LSA.
The engine does not know the difference between a 108, and a 114 LSA. It only sees the result of when the valves are opening, and closing. That changes, with duration, intake centerlines, exhaust centerlines, and so on.
A cam with a 114 LSA, may have a 110ICL. Also referred to as, 4* of advance built in. A cam with 108 LSA, might have an ICL, of 106*, or 2 deg of advance built in. What changes, is the valves opening and closing points, assuming duration hasn't changed.
As stated, overlap, is what matters. 114 LSA, doesn't mean you'll have less overlap, than a different cam, that has a 110 LSA.
A good example, would be, the HP500 cam, vs the 525 EFI cam. The HP500 cam, has 110 LSA, and 525 EFI cam, has 114 LSA. However, OVERLAP,
HP500=5* overlap
525EFI = 12* overlap
The HP500 cam, is a 222/230 110 LSA. The 525 EFI cam, is 236/244 114 LSA.
03-02-2017, 03:23 PM
#15
Joe in the artical they are saying the cams have identical lift/duration numbers, but they show the intake valve closing at different points 36,42,44 abdc for 101,107, 113 respectively.
Comp cams guy states in the piece "a cam with a tighter LSA is always going to have more overlap" which according to your example just isn't true. In the end I guess it would have been nice to see the cam cards for all three to get the full story.
Comp cams guy states in the piece "a cam with a tighter LSA is always going to have more overlap" which according to your example just isn't true. In the end I guess it would have been nice to see the cam cards for all three to get the full story.
capitalizing on swept volume and reducing or eliminating pumping losses is key to making any engine rock!! IMHO
03-02-2017, 04:36 PM
#16
Registered
iTrader: (1)
I swear this to be true.
03-02-2017, 05:32 PM
#17
Registered
iTrader: (3)
Overlap, has been the "DEVIL" in marine engines, for the past 3 decades, or longer. First, most don't truly understand what a camshaft is doing, so they keep repeating what they heard. 114 LSA is good, 110 LSA is bad.
They heard 110 LSA will revert, 114 wont. There is zero thought, into the big picture of things.
They heard 110 LSA will idle like crap, and 114 will idle smooth. Again, zero thought put into the big picture.
The truth is, overlap, is NOT the enemy. Overlap, is what helps make power. In todays world, we aren't limited to underwater exhaust, or wet exhaust, to silence the engines. There are plenty of sound options available. We have modern igntion systems, and EFI systems, that can help engines with a fair amount of overlap, idle well. We have exhaust, and intake options, that can help take advantage of what overlap can provide.
Today, everyone is building BIG engines. They want 540s, they want 572's, they want 598s, they want 632's. But yet, they still want to cam the engines, like they are dealing with the 454 they had in their first 19ft runabout in 1984. The other day, I was reading an old thread here on oso, from about 12-13 years ago. Some guys, were recommending a 731 cam, in a 598!!! Some said "maybe the 741 if you wanna step it up a notch". Are you kidding me? lol. A 230/236 hyd in a 600 inch engine??
And still guys make statements like "oso tech isnt what it used to be". Well thank god!!! Because we would still be running around with 600inch engines making .9hp per ci, and thinking a set of "revolution marine" exhaust manifolds were the best thing since sliced bread.
They heard 110 LSA will revert, 114 wont. There is zero thought, into the big picture of things.
They heard 110 LSA will idle like crap, and 114 will idle smooth. Again, zero thought put into the big picture.
The truth is, overlap, is NOT the enemy. Overlap, is what helps make power. In todays world, we aren't limited to underwater exhaust, or wet exhaust, to silence the engines. There are plenty of sound options available. We have modern igntion systems, and EFI systems, that can help engines with a fair amount of overlap, idle well. We have exhaust, and intake options, that can help take advantage of what overlap can provide.
Today, everyone is building BIG engines. They want 540s, they want 572's, they want 598s, they want 632's. But yet, they still want to cam the engines, like they are dealing with the 454 they had in their first 19ft runabout in 1984. The other day, I was reading an old thread here on oso, from about 12-13 years ago. Some guys, were recommending a 731 cam, in a 598!!! Some said "maybe the 741 if you wanna step it up a notch". Are you kidding me? lol. A 230/236 hyd in a 600 inch engine??
And still guys make statements like "oso tech isnt what it used to be". Well thank god!!! Because we would still be running around with 600inch engines making .9hp per ci, and thinking a set of "revolution marine" exhaust manifolds were the best thing since sliced bread.
03-02-2017, 08:18 PM
#19
Registered
iTrader: (1)
So how does a neophyte as myself figure this out? I was getting ready to yank the motor to pull the ZZ502 cam with 110* lsa out for the 741 112* just for the reversion risk, and even looking at the 525EFI cam with its 114*, but it sounds like this stufff can all get washed out anyways. A quick check on that google thingamajig lent towards needing cam cards and a 'puter program to sort it out.
Last edited by Baja Rooster; 03-02-2017 at 08:21 PM.
03-03-2017, 10:38 AM
#20
So how does a neophyte as myself figure this out? I was getting ready to yank the motor to pull the ZZ502 cam with 110* lsa out for the 741 112* just for the reversion risk, and even looking at the 525EFI cam with its 114*, but it sounds like this stufff can all get washed out anyways. A quick check on that google thingamajig lent towards needing cam cards and a 'puter program to sort it out.
