Aggressive cam lobes?
10-18-2014, 05:04 PM
#21
Le Mans Master
Member Since: Aug 2005
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St. Jude Donor '13-'14-'15
Back in the day, GM speced 15-50w Mobil-1 oil in the C5 I believe, does anyone recall any after-market cam failures, certainly few stock ones are reported if at all?
My point again for the Dexos1 5-30w being not appropriate for a vette owner that cares to keep it a while.
By specifying on the C7 that 15-50w is to be used to maintain warranty on track days (Z51 only) GM in effect is saying that the Dexos1 oil is only warrantable up to about a 20% duty cycle for tooling around within national speed limits.
If higher power levels are called for such as track duty the 15-50 Mobil 1 is the minimum requirement to protect the engine and keep the 100,000 mile warranty.
That should tell everyone what to use if you like to floor it at times track or not.
It is at your own risk that with the GM black box info that can show one ripping off 5-redline shifts in succession (track or not) just prior to a failure, the claim can be denied if you had 5-30 oil in the crankcase.
I would always keep the 15-50 in the sump that way GM even if misinterpreting black box data as track use has no reason to duck the warranty.
My point again for the Dexos1 5-30w being not appropriate for a vette owner that cares to keep it a while.
By specifying on the C7 that 15-50w is to be used to maintain warranty on track days (Z51 only) GM in effect is saying that the Dexos1 oil is only warrantable up to about a 20% duty cycle for tooling around within national speed limits.
If higher power levels are called for such as track duty the 15-50 Mobil 1 is the minimum requirement to protect the engine and keep the 100,000 mile warranty.
That should tell everyone what to use if you like to floor it at times track or not.
It is at your own risk that with the GM black box info that can show one ripping off 5-redline shifts in succession (track or not) just prior to a failure, the claim can be denied if you had 5-30 oil in the crankcase.
I would always keep the 15-50 in the sump that way GM even if misinterpreting black box data as track use has no reason to duck the warranty.
Thks again !!!!
10-22-2014, 07:42 PM
#22
Most people here want aggressive cam lobes. Why? Because someone told them they are better. So what is an aggressive cam lobe? To take the most advantage of the LS Chevy engine design the cam lobe must be smooth and stable. Generally in this LS Chevy engine, the smoother and more stable the cam lobe, the more power and RPM capability the engine will have. So generally the less aggressive lobe will make for the most aggressive (powerful) engine.
There is no need in having 8 different lobe styles or variations for the LS Chevy hydraulic cams. Most of the engine combinations I see on here run from idle to 6500 RPM with a valve lift from .550” to .650” lift and with spring seat pressure 130lbs to155lbs with 350lbs to 400lbs open pressure. The measurable differences in these lobes are very slight, the real difference is that some of them operate very well and others do not. The “hard” or “aggressive” lobes may make a small amount more vacuum at idle and may show a two pound gain in torque at 4000RPM but will cause more valve noise and float the valves sooner plus having a destructive affect on valve train parts and valve seat sealing. The “softer” lobes will have a little less vacuum at idle but provide quite valve train operation and extend the valve “float” RPM 300-500 RPM and do not destroy valve train components.
What do you call “aggressive? Is it high acceleration or high velocity? Which is harder on the valve train? The cam with higher lifter acceleration rates will be harder on the valve train.
Let us compare technical data on two lobes both with 230 degrees duration at .050” with .350” lobe lift. One lobe we’ll call “hard” the other “soft” even though I don’t like to use the word “soft”, but it is soft compared to the hard lobe. I prefer to call it the correct lobe for your engine.
Compare:
HARD SOFT
MAX ACCELERATION: .00037 .000323
MAX VELOCITY: .0073 .00775
NOSE ACCELERATION: .00023 .000212
So which one is more “aggressive”? The soft one moves the valve FASTER or higher speed. So what is aggressive? One of the reasons the hard lobe floats the valve sooner is because it has higher “nose” acceleration, which is negative acceleration at the top of the lobe.
There is no need in having 8 different lobe styles or variations for the LS Chevy hydraulic cams. Most of the engine combinations I see on here run from idle to 6500 RPM with a valve lift from .550” to .650” lift and with spring seat pressure 130lbs to155lbs with 350lbs to 400lbs open pressure. The measurable differences in these lobes are very slight, the real difference is that some of them operate very well and others do not. The “hard” or “aggressive” lobes may make a small amount more vacuum at idle and may show a two pound gain in torque at 4000RPM but will cause more valve noise and float the valves sooner plus having a destructive affect on valve train parts and valve seat sealing. The “softer” lobes will have a little less vacuum at idle but provide quite valve train operation and extend the valve “float” RPM 300-500 RPM and do not destroy valve train components.
What do you call “aggressive? Is it high acceleration or high velocity? Which is harder on the valve train? The cam with higher lifter acceleration rates will be harder on the valve train.
Let us compare technical data on two lobes both with 230 degrees duration at .050” with .350” lobe lift. One lobe we’ll call “hard” the other “soft” even though I don’t like to use the word “soft”, but it is soft compared to the hard lobe. I prefer to call it the correct lobe for your engine.
Compare:
HARD SOFT
MAX ACCELERATION: .00037 .000323
MAX VELOCITY: .0073 .00775
NOSE ACCELERATION: .00023 .000212
So which one is more “aggressive”? The soft one moves the valve FASTER or higher speed. So what is aggressive? One of the reasons the hard lobe floats the valve sooner is because it has higher “nose” acceleration, which is negative acceleration at the top of the lobe.
Why would softer lobes have less vacuum at idle? Sounds like it should be the opposite? While opening the intake valve quickly would cause more air to rush into the cylinder, possibly creating more vacuum in the intake, it also seems that the rough lobes should also exacerbate the valve overlap event.
10-23-2014, 11:09 AM
#23
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Why would softer lobes have less vacuum at idle? Sounds like it should be the opposite? While opening the intake valve quickly would cause more air to rush into the cylinder, possibly creating more vacuum in the intake, it also seems that the rough lobes should also exacerbate the valve overlap event.
10-23-2014, 11:51 AM
#24
Why would softer lobes have less vacuum at idle? Sounds like it should be the opposite? While opening the intake valve quickly would cause more air to rush into the cylinder, possibly creating more vacuum in the intake, it also seems that the rough lobes should also exacerbate the valve overlap event.
In order to compare soft opening and closing camshafts with "aggressive" high acceleration opening and closing camshaft it would make sense to keep area under the valve lift curve constant (which relates to having similar cylinder filling and evacuation, thus similar but not quite the same power, due to MEP differences).
In the case above the duration would have to increase, if centers not changed you would have a larger overlap and thus resulting lowering of idle quality.
What has been driving "aggressive" cam profile use (even at the OEM level) is reducing emissions and increasing fuel economy (efficiency) at the cost of some high rpm durability.