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.

 

i get what you are saying but i love the sound of a cam with a hard lope at idle with long tube headers.

 

The softer lobes will even sound better without the valve noise.

 

It's like pulling teeth to get cam details from the vendors on here lol

 

I don't think most people are talking about lobes when they are talking aggressive cams. They are talking about aggressive as in large cam for the size of the motor to get sound/power. You can have a tiny cam with really aggressive lobes, or an "aggressive" cam with really soft lobes. A 220/224 120LSA on XR lobes can be aggressive, or a 250/260 110LSA cam on really gentle lobes can be aggressive even if the ramps/lift isn't bad.

 

what he is talking about has nothing to do with the lope of the idle... he is talking about the aggressiveness of the actual lobe on the camshaft. What you're referring is more controlled by the cam's overlap, Which is determined by the duration and Lsa of the cam.

 

not duration
not lift
not lobe separation

......ramp rate.

 

Mostly because when someone spends thousands of dollars and hundreds of hours working on some good cam profiles they dont want to give out what they learned works for free. They paid for it in one way or another so why would they give them out for free?

 

I know why they do it but it's going in my motor and I paid for it I should get to know so I can calculate these things, use engine modeling software, etc. Vendors can play that game but it's a strike against you in my book. This is not NASCAR or Formula One.

 

If you buy one from them then yes, you should get your specs. Sorry, I misunderstood your statement.

 

I think when it comes to the NEW LT1 you may have to re-refine the meaning of aggressive----To me any cam that has to utilize a DOD delete or a VVT phase limiter should be considered an aggressive cam---Typically cam changes will only get you from 35-45 RWHP But on any LS3/LT1 DOD deleted and VVT limited HP gains of 100HP are seen all over the internet--I consider that an aggressive cam !!!

 

bought a cam and they wont give you specs? What is THAT
Probably a larger co's off the shelf cam
They just rename them. Mauler, Big monster, butt raper etc. Same stuff

Take your cam to a machinist if they have a Cam Dr they can runyour cam on there and print out every detail of it.

 

Knowing the ramp rate is important; if it is much higher than stock the Dexos spec 5-30 oil will not suffice to prevent wear.

The only way a cam of unknown spec has any place in a motor is if the speed shop provides a warranty beyond the cam only, but to all collateral damage the failing cam could be responsible for.

That would ensure that responsible decisions are made in specing out the cam, instead of being a Customer Guinea Pig

 

Yeah, if you want cam details don't order a Texas Speed and Performance cam.

 

What will wear and why?

 

The small block chevy always made do with small base circle cam lobes.

Before roller tappets were used steep ramp angles would cause very high contact pressure at the edge of the flat tappet lifter due to reduced contact area at the ramp of the lobe on aggressive after market cams.

The result was additional wear due to oil film strength being exceeded, this progressed to a point where the lifter broke through the hardened cam lobe surface, result cam failure.

Now with roller tappets having a rolling friction environment at the critical lobe ramp are puts less stress on the oil film, all is good.

Till cam grinders got more aggressive again, now in addition to having oil film strength challenged at the lifter and lobe ramp interface, the small base circle combined with the small lifter diameter creates a geometry that imposes large lateral forces that need to be countered by the lifter bores and cam bearings and again the thin surface hardening of cam lobes.

As the limits are pushed with a too aggressive of an ramp rate one of those 3-areas will let go first the others will follow in short succession

When ever an engine was originally designed for higher RPM capability (small block chev) by down sizing all valve train components one has to respect the limits the resulting geometry imposes on any after market cam design.

I believe the initial wear will start at ramp area then once hardened surface is compromised; material will be scooped out at the cam lobe nose as well.

The small diameter roller on the lifter cannot navigate this rough surface resulting massive increase in friction and pending loss of valve control

 

One piece of good news is the Comp Cams with the bigger fuel pump lobes are using through hardened tool steel cores. http://www.compcams.com/whatsnew/New...yID=-565312824

 

Well written with the exception of the amount of friction at the roller lifter/cam lobe interface, there is very little friction associated with rolling elements especially relative to sliding friction associated with flat tappet lifters. I really want you to explain why using Dexos1 is not sufficient to prevent "wear". I'm assuming you have a degree in tribology with at least a minor in rheology as it relates to viscosity.

I'll go ahead and say I disagree with your statement that Dexos1 is not sufficient to prevent wear. I'm not saying it will prevent wear, just saying all oils will not prevent the type of wear seen with aggressive cams. I'm mainly wondering why you are singling out Dexos1 as the only oil that will result in failure. What tests have you conducted that you can present to the forum as proof to back up your statement?

 

You are correct to take issue with my statement:

"Till cam grinders got more aggressive again, now in addition to having oil film strength challenged at the lifter and lobe ramp interface, the small base circle combined with the small lifter diameter creates a geometry that imposes large lateral forces that need to be countered by the lifter bores and cam bearings and again the thin surface hardening of cam lobes."

It appears to contradict my earlier statement:

"Now with roller tappets having a rolling friction environment at the critical lobe ramp puts less stress on the oil film, all is good."

I need to elaborate on my thinking here: My thesis or theory here is based on valve bounce occurring at the rev limiter setting per testing done by Katech, they are of the opinion there should be at least 500-rpm cushion between limiter and valve train instability events:

"we prefer to see a 500-800-rpm safety margin, which would mean a 6,300-6,600-rpm rev limit."

Read more: http://www.superchevy.com/how-to/140...#ixzz3G441hLj9

The point I am making if the valve bounces it is no longer following the cam lobe profile, which means the roller lifter can bounce or lift from the cam lobe surface momentarily.

Fact: rockwell hardness testing is not reliable on an induction hardened or nitrited surface due to the give of the underlying unhardened base metal.

My postulate is that the impact pressure of the tiny roller contact surface is analogous to the point pressure involved in hardness testing.

The relatively soft base metal will not support the hardened thin layer from a concentrated impact load which would flex and create a spalled cam lobe surface.
This would progress in continued spalling analogous to an 18-wheeler cracking a concrete slab at a week point in the supporting road bed till the whole Hyway slab is pulverized from the continued contact pressure of loaded trucks.

Even though in a perfect model the roller lifter has no friction at the cam lobe thus not an oil dependent environment.

My imperfect environment model requires that the oil is tasked with cushioning lifter on lobe impacts rather than just rolling friction, this requires a much higher shear strength to maintain sufficient oil film thickness than a 5-30W can provide I would prefer a Redline 10-60W for providing sufficient cushion for repeated red-line float induced impact events, this would also protect the lifter bores from eccentric wear that allow lifter rock from the large side loading (geometry induced) as the lifter is pushed sideways trying to climb a steep ramp at high acceleration rate.

GM engineers expressed concern about the Dexos1 oil film strength to the point it dictated their design and limited choices:

"Our analysis capability is really good for oil film thickness. This analysis comprehends engine speeds, loads, temperature, mass/inertia and geometry. At high speed, you have a lot of inertia, a lot of reciprocating mass which will reduce oil film thickness. We had to make a big move to increase the film thickness robustness. That (a titanium rod) was the most straight forward way to do it."

That begs the question: rather than an expensive set of Ti rods, why not just a better engine oil? You can buy a lot of premium, ester-based, 10W30 synthetic oil, which has better film-strength properties, for the cost of those rods.

Well...it's just not that simple. To use forged steel rods and a higher film-strength oil, General Motors would, first, have to admit that fabled Mobil 1 5W30 and its "Dexos 1" successor, were inadequate for use in the LS7. That was so not-gonna-happen."

see: http://www.camaro5.com/forums/showthread.php?t=285402

BTW, I have no credentials you speak of, just my critical thinking based on a culmination 40-years of being a car enthusiast reading every magazine and car related article in sight, having worked on and owned 37 cars some racing at Gingerman looking at an Alpha Romeo 4c, LT1 or Z28 for some track fun.

 

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.