speedtigger

iTrader: (16)

A question cam up in another thread that inspired what I thought would make a great thread of its own. Some people may wonder what is different about an aftermarket performance camshaft that makes it perform better than the factory OEM performance camshafts like the LS7 cam.

Here is my explanation why the wide lobe center, late intake centerline OEM camshafts don't make as much average power as a properly chosen aftermarket performance camshaft.

To get started, lets look at the valve events of the LS7 cam:

Specs@ .050":211-230 on 121 LSA
Intake Valve Open: 15 ATDC
Intake Valve Close: 46.5 ABDC
Exhaust Valve Open: 56 BBDC
Exhaust Valve Close: 6 BTDC
Overlap @ .050" = -21

If you have a lot of familiarity with the valve events of performance camshafts, one valve event above really stands out. That is the intake valve open of 15 degrees after top dead center. That valve event right there is what is hurting the overall performance of this camshaft the most. If you were to change just that valve event from 15 degrees after top dead center to a much earlier "0" degrees, this camshafts performance would increase dramatically.

Opening the valve earlier would help feed the engines cylinder much more efficiently. The reason for this is that, like most domestic V8 engines, the LS engine will reach peak piston speed on the intake stroke at about 70-75 degrees after top dead center. Once you compare this to the LS7 cam's intake centerline of 121 degrees, you can see that the engines cylinder is at peak demand 50 degrees before the camshaft reaches peak lift. This dynamic right here is one of the main reasons that aftermarket performance camshaft open the intake valve sooner. It allows the valve to be open further when the engine wants the air and fuel the most.

So, you say lets just advance the LS7 camshaft. You can. And it will help low end power by getting the valve open sooner to feed the engine at peak demand and closing the the intake valve sooner to help trap more cylinder pressure at lower RPMs. But, it will also open the exhaust sooner which may waste some torque at low RPM and close the exhaust valve sooner which will diminish final cylinder evacuation at the end of the exhaust stroke leaving behind more burned air and fuel to contaminate the subsequent intake stroke. On top of that, the LS7 camshaft will still lack overlap compared to an aftermarket performance camshaft which results in less upper RPM power. Let's look at the valve events of the LS7 camshaft advanced and highlight the positive effects in green and the negative effects in red:

Specs@ .050":211-230 on 121 LSA +6
Intake Valve Open: 9 ATDC
Intake Valve Close: 40.5 ABDC
Exhaust Valve Open: 62 BBDC
Exhaust Valve Close: 12 BTDC
Overlap @ .050" = -21

As you can see, the intake valve events have gotten better even though the intake valve open is still late compared to a proper performance camshaft. However, the exhaust events have gotten more out of line. The most detrimental would likely be the very early exhaust close of 12 degrees before top dead center.

Now, lets go in a different direction. Let's take that LS7 cam and change just two valve events. We will change the intake valve open and the exhaust valve close to "0" degrees at .050". This is what we would get:

Specs@ .050":226-236 on 115.5 LSA +2
Intake Valve Open: 0 ATDC
Intake Valve Close: 46.5 ABDC
Exhaust Valve Open: 56 BBDC
Exhaust Valve Close: 0 BTDC
Overlap @ .050" = 0

As you can see, this new revised version of the LS7 camshaft would still have 0 degrees of overlap at .050" which would make for a very nice driving performance camshaft with a mild idle and good drivability and would probably rip pretty good.

Some may be tempted to ask why GM doesn't do this. The reason is that even though us automotive performance enthusiasts would find the idle and drivability totally acceptable with this cam, GM requires and even smoother idle, less emissions and more engine vacuum. So they trade performance to achieve their standards.

Lastly, lets look at a performance camshaft that you could use in a 5.3-6.2 liter engine instead of the LS7 cam that will outperform it from idle to redline:
Cam Motion Titan II
Specs@ .050":221/226 on 112 LSA
Intake Valve Open: .5 BTDC
Intake Valve Close: 40.5 ABDC
Exhaust Valve Open: 47 BBDC
Exhaust Valve Close: 1 BTDC
Overlap @ .050" = -.5

The Titan 2 camshaft still has -.5 overlap, so like our revision to the LS7 cam above, it will have great drivability and would be very comfortable as a daily driver camshaft. However, take note of the intake valve close event. It is 6 degrees earlier than the LS7 camshaft. This will allow the Titan II camshaft to capture more cylinder pressure at low RPM and make more torque sooner than the LS7 camshaft. And, even though it has an earlier intake valve close, it will still make more power in the upper RPMs because it will fill the cylinder so much more efficiently at peak demand on the intake stroke. Then throw in the additional power that is created in the upper RPM due to the additional overlap, and it is just superior across the board.

This is why a properly chosen aftermarket camshaft out-performs the OEM performance engine cams like the LS6 & LS7 cam.

1FastBrick

iTrader: (16)

Excellent post and a great comparison!!!

thunderstruck507

iTrader: (18)

Building on this, cstraub has a post on the Chevelle forum right now about how marketing resulted in the way we look a just a small fraction of a cam as its "specs" when the lobe shape can lead to 2 cams that look the same as far as duration and lift specs can perform completely differently.

I could be wrong but I have serious doubts the OEM camshaft is as rapid as an aftermarket lobe (even a non-violent/smooth lobe).

If you get bored maybe you could do a post like your OP comparing the events of an early LS6 cam to the CM stage 2 5.3 cam I have. Their duration and lift specs are nearly the same IIRC.

mOtOrHeAd MiKe

iTrader: (8)

I am certain that if GM didn't have so many constraints placed upon them the cam specs would look very different from the factory; assuming reliability could be maintained.

That being said I specifically chose an LS9 cam for our TBSS' Procharged LS2 simply because it met the criteria of smooth idling, emissions friendly, and great driveability. I could have gone with an augmented version of an LS9 cam or used another more aggressive bump stick I have on the shelf - but, that would defeat the aim. And possibly exceed other drivetrain limitations from the added power adding additional cost and headaches to the project.

I whole-heartedly agree with your analysis about what influences what when looking at options. But, a lot of power can still be made with OEM grinds depending upon the application.

PS. I have a CamMotion cam waiting to go in our wagon's LS1 and it doesn't look anything like stock (actually specs out a lot like the cam you descibed above).

Mercier

iTrader: (15)

But what about my carbon footprint?!

Great, illustrative, easy to understand write-up on this oft misunderstood subject.

svslow

This is a good comparison. I agree that the average power made with an aftermarket cam will be higher. However, I have been curious what the difference in peak power would be on a turbo application with a stalled auto that will live mostly in the 5000-7000 rpm range on a pass. I understand there are a lot of factors here, let's just say we are comparing a mostly stock 5.3 with a 75-ish mm turbo with a LS7/9 cam vs. aftermarket.

Any insights on this?

Nostang

iTrader: (4)

OEM cams put priority on different things then car guys. #1 CA emissions compliance #2 emissions compliance for everyone else #3 Fed gov't gas mileage standards #4 reliability #5 performance.

Car guys priority. #1 how much more power can I make #2 overall performance #3 how often do I need to change valve springs. lol

Good write up!

speedtigger

iTrader: (16)

When you say rapid, I would want to clarify between velocity and acceleration. Ideally I would want to achieve as high of a velocity as needed but with smooth acceleration. This creates the most stable, reliable lobes. The OEM LS cams have a lot of seat timing. Meaning that they lift up the valve off of the seat and set them down on the valve seat very gently relatively speaking. However once past that, they have a lot of acceleration. So, they are not as smooth as you might think. Certainly something that can be improved on from a stability standpoint.

This actually reminds me of a magazine article where they dyno tested all of the OEM LS camshafts back to back. In this test, the LS2 camshaft experienced valve float problems. It was the only camshaft to float the valves while still in its power curve. Next up they dyno'd the LS3 camshaft which did not have any valve float problems. What makes this interesting is that the LS3 camshaft has almost the exact same listed specs as the LS2 camshaft with the exception of one thing: the Ls3 camshaft had an intake valve lift of .551" vs. the LS2's intake valve lift of only .525". This likely surprised most people that the camshaft with more lift was more stable than the camshaft with less lift, but this is likely just a great lesson in lobe design. More lift does not automatically mean the lobe is more aggressive and has more peak acceleration. A smoother lobe can achieve a higher average velocity and lift the valve higher while still maintaining better stability and RPM capability.

The LS6 camshaft is very similar to the LS7 camshaft and the other OEM LS camshafts in that it has a very late intake valve open and early exhaust valve close when compared to a typical aftermarket performance camshaft.

Specs@ .050":204-218 on 117.5 LSA
Intake Valve Open: 16 ATDC
Intake Valve Close: 40 ABDC
Exhaust Valve Open: 46 BBDC
Exhaust Valve Close: 8 BTDC
Overlap @ .050" = -24

The noteworthy differences between the LS7 camshaft and the LS6 camshaft is that the LS6 camshaft has a about a 7 degree earlier intake valve close and about 8 degree earlier on the exhaust valve close. This is partially because the LS7 is 50+ cubic inches bigger and maybe GM wanted to be a little more aggressive for their flagship performance engine.

Looking at the same Cam Motion performance camshaft you will see some striking similarities:

Cam Motion Titan II
Specs@ .050":221/226 on 112 LSA
Intake Valve Open: .5 BTDC
Intake Valve Close: 40.5 ABDC
Exhaust Valve Open: 47 BBDC
Exhaust Valve Close: 1 BTDC
Overlap @ .050" = -.5

Notice how the intake valve close and the exhaust valve open numbers are almost identical. It is only the intake valve open and exhaust valve close numbers that are drastically different, yet the specs that everyone are familiar with look drastically different. Who would believe that a 204/218 on 117.5 LSA would have so much in common with a a 221/226 on 112 LSA? However, the IVO and EVC differences count for a lot in performance. Likely to the tune of about 25+ horsepower and lots of average torque under the curve.

JakeFusion

iTrader: (7)

I swapped from a 234/242 111+3 Cam on EPS lobes to a 227/244 115+5 on LSL/XE lobes. The IVC isn't far apart nor is the EVC. But the overlap is very different. Tuning the cam this weekend hopefully and should be able to provide a pretty good A-B comparison between a "stage 2" type cam and a more *****-to-wall type cam. Peak power I don't expect a huge difference. Under the curve I expect more... along with much better manners.

Darth_V8r

iTrader: (4)

This is due to the oft-overlooked 0.200 lift point. The stock ramp rates from .006-.050 are extremely gentle compared most cams we look at on this site - even the "endurance" lobe cams. You might see 80 degree ramp rates from GM vs 47-55 aftermarket. However, a poorly chosen 0.200 lift point can mean the lobe is very mild until .200, suddenly jerks to full lift, pole-vaulting the valve, drops very quickly, and then sets it nice and softly on the seat. A well-chosen 0.200 event would both move and accelerate incredibly fast to 80% lift, slow down, gently go over the peak lift, come down fast, and then gently return to the seat. The 006 to 050 ramp rate is indicative of how softly the valve will return to its seat, but not necessarily indicative of smooth travel for the rest of the lobe.


I would think that the added cubic inches would require additional duration simply to be able to breathe. It's air input requirements are pretty high. Also, the later IVC and earlier EVO help support higher RPM performance, which the LS7 is designed for.

Got another one for you:

Cam 1: 227/235-112+3
Cam 2: 231/235-113+2

Actual comments -
* Cam 1 has tighter LSA, so will chop more, be harder to drive, etc
* Cam 1 has a more advance and higher split, so will be better for torque
* Cam 2 has wider LSA, will be easier to drive
* Cam 2, not enough split
* Cam 1, too much split

Now, look at valve events:

Event......Cam1......Cam2
IVO.........4.5...........4.5..BTDC
IVC.........42.5.........46.5.ABDC
EVO........52.5.........52.5.BBDC
EVC........2.5...........2.5...ATDC
Overlap....7..............7....Degrees

Only difference is one valve event - intake valve close - is four degrees later. Everything else is perfectly identical. The point here is how the specs for two very similar cams can appear quite different.

So, in reality, the cams should both idle identically and have similar daily driveability. Cam 1 with earlier IVC is better suited to low and midrange power and will likely peak a bit lower in the RPM band. Cam 2 will likely support higher RPM and peak a bit later in the RPM band.

speedtigger

iTrader: (16)

With the popularity of turbos these days, this is a really great example to look at. And like yourself, I have seen many choose the LS9 camshaft for their turbo build. So, lets look at the specs:

GM LS9
Specs@ .050":211-230 on 122.5 LSA ( I read that somebody measured theirs -1.5 degrees of advance, but lets look at it straight up for this exercise)
Intake Valve Open: 17 ATDC
Intake Valve Close: 48 ABDC
Exhaust Valve Open: 57.5 BBDC
Exhaust Valve Close: 7.5 BTDC
Overlap @ .050" = -24.5

Obviously, this cam is very similar to the LS7 cam. It is just a slightly wider lobe separation angle and the lobes are designed for 1.7 rockers vs the LS7 lobes which were intended for 1.8 rockers. And, just like the other OEM LS cams, this camshaft also has a very late intake valve open and pretty late exhaust valve close.

The next notable thing is that the intake valve close is 48 degrees after bottom dead center. In a naturally aspirated 6.2 liter engine, this would be a pretty aggressive IVC aimed at achieving a higher peak RPM. However, since the LS9 engine has a positive displacement supercharger which are incredibly efficient at lower RPMs, this later intake valve close has a nice effect of stretching the powerband upward with totally acceptable losses at lower RPM in that engine's application. Conversely, turbochargers tend to stretch the engine powerband higher for a given engine. And in turbo applications, power before the engine comes into boost is often found lacking. So, that late of an IVC may not be desirable for a street driven turbocharged LS. In addition, it will also likely make turbo combos with tight stall converter a little lazy and flat down low.

Moving on to the exhaust valve close, unlike the naturally aspirated engine where we want to close the exhaust valve later, in a mild or street driven turbo LS engine we may not want to do that. With a turbo engine we have pressure in the exhaust that is greater than the pressure of the intake manifold, so limiting overlap is very helpful in spool times and lower RPM performance that is desirable in street driven cars. So the 7.5 before top dead center exhaust valve close can be a nice number in a mild and/or street driven application.

Lets look at a typical performance aftermarket street driven turbo cam. This is the Cam Motion Turbo Stage 2 camshaft:
Specs @ .050" 226/220 15+4 .595"/.578"
Intake Valve Open: 2 BTDC
Intake Valve Close: 44 ABDC
Exhaust Valve Open: 49 BBDC
Exhaust Valve Close: 9 BTDC
Overlap @ .050" = -7

IVO:
As you can see, just like a naturally aspirated camshaft, there is benefit to opening the intake valve sooner from a performance standpoint. It is the same reason it is beneficial in the naturally aspirated engine as mentioned above.
IVC:
This performance camshaft has an intake valve close of 44 degrees after bottom dead center. This valve event is similar to what a naturally aspirated engine might like for a camshaft of similar duration.
EVO:
You might have noticed that the exhaust valve open on the turbo camshaft is quite a bit later than the LS9 supercharger camshaft. This is because in a supercharged engine, the extra power created by the supercharger needs to be let out sooner to get all of the exhaust out effectively and eliminate pumping losses. But, unlike a supercharged engine where the exhaust goes straight out the tailpipe, a turbo charged engine uses the exhaust to drive the impeller of the turbo. So, we do not benefit in eliminating pumping losses as much because there is still pressure in the exhaust caused by the restriction of the turbo. In addition, the timing of the exhaust valve open has other effects on the turbocharged engine exhaust. As the piston moves down the cylinder on the power stroke the pressure is dropping rapidly in the cylinder, so is the temperature. So, an earlier exhaust valve open means more pressure and heat going into the exhaust to drive the turbo. However, it also means less pressure and heat expansion in the cylinder to drive the piston down and make power. All of this leaves us with a complex relationship between this important turbo cam valve timing event and the flow and design of the turbo charger and exhaust system.
EVC:
The exhaust valve close of this performance turbo camshaft is 9 before top dead center at .050". As discussed earlier, this is a spec that is very similar to the LS9's 7.5 degrees BTDC. This is one spec of the LS9 cam that is really pretty spot on for a typical street turbo engine.

So to speak directly to the question that was posed about peak power, I would say that absolute peak power with the Cam Motion Turbo Stage 2 camshaft might be the same 25+ horsepower that the Titan II would gain over an LS6 cam in a naturally aspirated engine. However, I think you will find that it will be more responsive, drive better, spool faster and probably have less pressure differential between the intake and exhaust pressures. All of those improvements could make a really nice difference in the experience of driving your car as well as going faster.

svslow

That is exactly the answer I was looking for, thank you.

speedtigger

iTrader: (16)

This actually coincides with the next example perfectly.

I want to take this example even further to make a point about IVO, EVC and overlap. Let's take a look at this same LS7 camshaft that we modified in the quoted post and open the intake valve even sooner and closing the exhaust valve even later. In fact, lets take them as far as I consider safe on an LS1/LS2/LS6 engine. Here is what you get:

Specs@ .050":236-243 on 111.5 LSA +3
Intake Valve Open: 9.5 BTDC
Intake Valve Close: 46.5 ABDC
Exhaust Valve Open: 56 BBDC
Exhaust Valve Close: 7 ATDC
Overlap @ .050" = 16.5

Now we have a serious thumping, hard loping barnstormer of a camshaft. In fact it is nearly identical in .050" specs to Cam Motion's max effort street/strip camshaft the Titan King LS1 Camshaft:\

Specs@ .050":236-244 on 112 LSA +3
Intake Valve Open: 9 BTDC
Intake Valve Close: 47 ABDC
Exhaust Valve Open: 57 BBDC
Exhaust Valve Close: 7 ATDC
Overlap @ .050" = 16

Pretty amazing the similarity isn't it? Before anyone gets out their tin-foil hat, I assure you that this coincidence is just a simple result of two designers knowing what works for a given particular application. This too is the same reason for the differences. GM needed -21 degress of overlap @.050" to the get the driving and behavioral characteristics they needed. The performance aftermarket knows that a LS street enthusiast will have no problem at all with the driving characteristics of 0 degrees of overlap and they also know that the max effort guy will have no problem with the nasty idle of 16 degrees of overlap @ .050".

So, now we have 3 camshafts that all have the exact same intake valve close and exhaust valve open cam timing/valve events as the original LS7 camshaft. I think this is just a great illustration of where the power is coming from when you go to a well chosen aftermarket grind.

The original LS7 camshaft 0f 211/230 on 121 LSA has -21 degrees of overlap. The 1st revised version we made came in at 226/236 with a 115.5 LSA and 0 degrees of overlap at .050" and the last revision we made cam in at 236/243 on 111.5 LSa and a healthy 16 degrees of overlap.

The OEM version will have the best manners and the least power. The revised version 226/236 115.5 version will still have very good manners and could make 15-25 HP more power. While the 236/243 111.5 version is not about manners. It is about getting as much power as possible and might make another 10-15 HP more over the 226/236.

So in summary, opening the intake valve sooner will make more power within limitations because it makes the intake stroke more efficient by getting the intake open sooner and further at peak intake stroke demand. Closing the exhaust later will make more because it cleans the cylinder of burnt exhaust gasses better for a cleaner charge on the next intake stroke. And, the combination of these two creates overlap which capitalizes on the low pressure pulse of the existing exhaust velocity to draw in more are on the intake tract on the subsequent intake stroke increasing volumetric efficiency even more.

speedtigger

iTrader: (16)

I thought of you when I saw this thread of a member reporting his results of switching from an LS9 cam to a mild single pattern aftermarket cam on his turbo LS: https://ls1tech.com/forums/forced-in...l#post19292263