Cam and valvetrain longevity....??? low duration high lift...
11-04-2016, 05:05 PM
#1533
Platinum Member
Platinum Member
Love how it's still my fault after putting 65 hours of use on my engines... The only issues were not my building but everything Bob had a hand in...
Still have yet to see proven long term good results...
Still have yet to get that email back from Bob .....
The best part is I take a ton of heat for exposing Bob and putting every single last detail of my build out there for everyone to pick apart, most guys hide this stuff... I call it live and learn... Don't call Bob
Still have yet to see proven long term good results...
Still have yet to get that email back from Bob .....
The best part is I take a ton of heat for exposing Bob and putting every single last detail of my build out there for everyone to pick apart, most guys hide this stuff... I call it live and learn... Don't call Bob
11-04-2016, 05:25 PM
#1534
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Join Date: Oct 2005
Location: Olmsted Falls,Ohio Marblehead,Oh
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You stirred the pot, not me... Get off it ok? I had some faults yes, Bob played more of a role in them... So thx for your concern... I don't feel any need to keep explaining myself to you or any other bob sucker.
11-04-2016, 06:31 PM
#1535
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I know there are alot of guys who don't understand the effects of duration vs lift, lifter acceleration curves and so on. Let me try to explain , bear with me, I'm just a gravel hauling novice at this stuff.
Anyhow, we all know or heard about the proven Crane "741" and "651" cams. Lets look at their calculated lifter acceleration rate from my program. We have known these lobes to simply work, and not tear up parts. Merc used these lobe families in their 500efi, 525efi, and so on.
Crane 741 Intake lobe 298/236 , .632 Net lift = 2.96
Crane 651 intake lobe 306/251, .632 Net lift= 2.97
Now, here's comp cams Marine/HUC lobe designs
306/251 , .632 Net lift = 3.15
306/251, .680 Net lift = 3.42
326/271 , .680 Net lift = 3.31
326/271, .632 Net lift = 3.17
What you see here, is when you compare two cams, with the same durations, and increase the lift, the lifter acceleration factor simply increases. Now, look at the smallest cam lobe comp offers with 680 lift. It has 251* of duration, with a lifter acceleration rate of 3.42. Moving to a 271* lobe with 680 lift, the lifter slows down, to 3.31. Now, what do you think would happen, if you went the other way, and went to 241* of duration, with 680 lift? The lifter acceleration, would be 3.49. Comp , crane, and others, must feel that is too much, so they don't offer it for a endurance bbc std cam size/lifter size setup.
Now, the seat duration can be increased to slow things down, while keeping the lift at 680. From the cam grinders I have talked to on that topic, basically said, its just not worth doing that. The slower ramp higher lift, will probably make less power than the faster ramp, with less lift.
Things can get much more aggressive with a solid profile, when you don't have a hydraulic mechanism in place, or the spring limitations a hyd setup faces. When you make a hyd lobe aggressive, you need more spring. When you use more spring, with the fast lobe, now the hyd mechanism, becomes the weak link. When the hydraulic mechanism can't cope, and you start losing valvetrain stability, you not only can tear stuff up, you also can lose power. Ask any camshaft/engine building expert who has pushed hyd cams to their limits, they find that the smoother, more stable lobes, usually make more power, and last longer, on a HYDRAULIC.
GM knew what they were doing on production engines. Running 483 lift hyd cams, with barely 100lbs of seat pressure, and sub 300 lbs of open pressure on a truck big block. That engine would not last 200k miles in a work truck, with a 600 lift cam, and 175/450 spring pressures. Imagine letting a engine like that, idle for 8 hours like some work trucks do on jobsites. The downside, was they made 325hp, and didn't rev past 4500rpm.
Anyhow, we all know or heard about the proven Crane "741" and "651" cams. Lets look at their calculated lifter acceleration rate from my program. We have known these lobes to simply work, and not tear up parts. Merc used these lobe families in their 500efi, 525efi, and so on.
Crane 741 Intake lobe 298/236 , .632 Net lift = 2.96
Crane 651 intake lobe 306/251, .632 Net lift= 2.97
Now, here's comp cams Marine/HUC lobe designs
306/251 , .632 Net lift = 3.15
306/251, .680 Net lift = 3.42
326/271 , .680 Net lift = 3.31
326/271, .632 Net lift = 3.17
What you see here, is when you compare two cams, with the same durations, and increase the lift, the lifter acceleration factor simply increases. Now, look at the smallest cam lobe comp offers with 680 lift. It has 251* of duration, with a lifter acceleration rate of 3.42. Moving to a 271* lobe with 680 lift, the lifter slows down, to 3.31. Now, what do you think would happen, if you went the other way, and went to 241* of duration, with 680 lift? The lifter acceleration, would be 3.49. Comp , crane, and others, must feel that is too much, so they don't offer it for a endurance bbc std cam size/lifter size setup.
Now, the seat duration can be increased to slow things down, while keeping the lift at 680. From the cam grinders I have talked to on that topic, basically said, its just not worth doing that. The slower ramp higher lift, will probably make less power than the faster ramp, with less lift.
Things can get much more aggressive with a solid profile, when you don't have a hydraulic mechanism in place, or the spring limitations a hyd setup faces. When you make a hyd lobe aggressive, you need more spring. When you use more spring, with the fast lobe, now the hyd mechanism, becomes the weak link. When the hydraulic mechanism can't cope, and you start losing valvetrain stability, you not only can tear stuff up, you also can lose power. Ask any camshaft/engine building expert who has pushed hyd cams to their limits, they find that the smoother, more stable lobes, usually make more power, and last longer, on a HYDRAULIC.
GM knew what they were doing on production engines. Running 483 lift hyd cams, with barely 100lbs of seat pressure, and sub 300 lbs of open pressure on a truck big block. That engine would not last 200k miles in a work truck, with a 600 lift cam, and 175/450 spring pressures. Imagine letting a engine like that, idle for 8 hours like some work trucks do on jobsites. The downside, was they made 325hp, and didn't rev past 4500rpm.
Last edited by MILD THUNDER; 11-04-2016 at 06:33 PM.
11-04-2016, 06:59 PM
#1536
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Full Force clean out your PM box 
11-04-2016, 07:45 PM
#1540
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I don't believe Jim is running .400 lobe lift, I think he is getting his lift from rocker ratio isn't he? And also running solid lifters?
