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Discussion Starter #1
Lets say you have two nearly ident cams. One has 106 degree lobe center while the other has 112 degree lobe center...in general what would the expected differences be between the two? :)
 

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69NovaSS said:
Lets say you have two nearly ident cams. One has 106 degree lobe center while the other has 112 degree lobe center...in general what would the expected differences be between the two? :)
read the new issue of car craft. it has exactly what you're talkin about.
 

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It depends on where you put the intake lobe center. If you had a 112° LSA and a 108° LSA cam with the identical intake lobes each set at 108° ICL, the DCR would be the same.
 

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It's Alt0176. If you click Start, Programs, Accessories, System Tools, Character Map you will come up with a chart of characters. You can either copy these characters directly, or use the keystrokes shown as you click on each individual one. (Ò¿Ó) Hold the Alt key down as you enter the numbers, then release the Alt key. You can get all kinds of characters like º,¹,²,³,¼,½,¾,Ω,π,♀,♂, and Arabic, Russian, Greek etc.
 

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Discussion Starter #7
I've been playing a lot lately with different combos on dyno2000 just trying to see how the various elements effect the overall package. Anyway the base motor that I use is loosely(very loosely) based on my motor. This "Dyno Mule" :rolleyes: runs a crane cam with 518/536 lift with @.050 duration of 244/252 this cam has 106 degree lobe centers. 11.0:1 CR, 2.02/1.60 factory heads, duel plane intake, 780 VAC carb, Large dia Headers with mufflers

Anyway quite by accident I discovered that crane makes another cam that is ALMOST a duplicat to the one in the Mule other than the lobe center is 112 and of course the overlap is different also . The 112 cam has 60 degrees of overlap while the 106 cam has 36 degrees of overlap. But the duration and lift specs are the same between the two cams and both are solid lifter cams.

Anyway to my surprise the 112 degree cam made a bit more power than the 106 degree cam did thoughout the entire RPM range.

So I started looking into how the different lobe centers effect the motor and found some info though I'm not sure how accurate it is.

I have read that motors with wider lobe center cams will idle better, be more fuel efficient, and make more power higher up than motors with narrow lobe centers with tend to build the torque earlier and peak out sooner...

Now not sure if the vol eff is an indication of MPG but the 112 cam has slightly better vol eff when you compair the two cams....

Is this what a person should expect with a wider lobe center cam? :confused:
 

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Discussion Starter #8 (Edited by Moderator)
If all other things are equal* what difference should I see going from a 106° lobe center cam to a 112° lobe center cam.

* Cam specs are the same except for the lobe center and overlap. The car is the exact same too. So with no other changes EXCEPT the cam what differences should a person see

BACKGROUND info:

69NovaSS said:
I've been playing a lot lately with different combos on dyno2000 just trying to see how the various elements effect the overall package. Anyway the base motor that I use is loosely(very loosely) based on my motor. This "Dyno Mule" :rolleyes: runs a crane cam with 518/536 lift with @.050 duration of 244/252 this cam has 106° lobe centers. 11.0:1 CR, 2.02/1.60 factory heads, duel plane intake, 780 VAC carb, Large dia Headers with mufflers

Anyway quite by accident I discovered that crane makes another cam that is ALMOST a duplicat to the one in the Mule other than the lobe center is 112° and of course the overlap is different also . The 112° cam has 60° of overlap while the 106° cam has 36° of overlap. But the duration and lift specs are the same between the two cams and both are solid lifter cams.

Anyway to my surprise the 112° cam made a bit more power than the 106° cam did thoughout the entire RPM range.

So I started looking into how the different lobe centers effect the motor and found some info though I'm not sure how accurate it is.

I have read that motors with wider lobe center cams will idle better, be more fuel efficient, and make more power higher up than motors with narrow lobe centers with tend to build the torque earlier and peak out sooner...

Now not sure if the vol eff is an indication of MPG but the 112° cam has slightly better vol eff when you compare the two cams....

Is this what a person should expect with a wider lobe center cam? :confused:
 

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From the Crane Site:

Camshaft Design For “Vacuum Rule” Engines

Many sanctioning bodies are using “vacuum rules” in their tech inspection for their entry-level racecars. These classes are designed to keep the cost of racing down. The tech inspectors know if the engine isn’t able to generate a high vacuum signal, there is a good chance of a race camshaft in the motor So, to prevent this from happening, these classes are required to pass a vacuum test.

There are several factors that affect the amount of vacuum the engine will produce. Those include:

# Cubic Inch of Engine (bigger being better)
# Compression Ratio (the higher the compression, the better)
# Installation of the Camshaft (installed in an advanced position can help)
# Amount of Camshaft Overlap (usually compared at the .050” tappet lift figures)
# Lobe Separation Angle (wider is better for vacuum, tighter is better for driveability)


The two most important factors are the cubic inch size of the engine and the amount of overlap that is generated by the camshaft. Overlap is the amount of degrees (time) that the intake valve and exhaust valve are open simultaneously. It is measured by adding the “intake opening event” and the “exhaust closing event” on your camshaft spec card. The more degrees of overlap, the lower the engine vacuum will be. Racing cams with increased duration, dual pattern designs and tight lobe separation angles will not produce the legal amount of vacuum. Therefore, smaller duration cams with wide lobe separations, like in a stock engine, will produce a higher amount of vacuum. So, the game is how far can we increase the duration and tighten the lobe separation to improve performance and still pass inspection. “Single Pattern” cams (with the same amount of duration on the intake and exhaust lobes) will have less overlap than a “Dual Pattern” cam (with more duration on the exhaust lobe). But “Upside-Down” cams (with less exhaust duration than the intake) may just be what you’re looking for.

Naturally, the rules are never quite the same from track to track as to the exact amount of vacuum they require and at what RPM it is to be measured. But for our discussion here, we’ll pick a rule that we’re familiar with. It requires that the engine generate 16 inches of vacuum when measured at 1,000 RPM idle speed and must run a hydraulic flat tappet cam. Here are three examples:

# 305 cu./in. engine single pattern cam with 218 / 218 duration and 110 lobe separation. (Intake opens at 4 degrees and the exhaust closes at -6 degrees = -2 degrees of overlap.) This cam has negative -2 degrees of overlap and will produce 16 to 17 inches of vacuum.

# 350 cu../in. engine single pattern cam with 222 / .222 duration and 110 lobe separation. (Intake opens at 6 degrees and the exhaust closes at -4 degrees = +2 degrees of overlap.) This cam has +2 degrees of overlap (4 degrees more overlap than the previous example) and still produces 16 to 17 inches of vacuum because the engine size is 45 cubic inches larger.

# A 350 engine with an upside-down cam 222 / .210 duration and a tight 107 lobe separation (Intake opens at 9 degrees and exhaust closes at -7 degrees = +2 degrees of overlap.) The cam will still have +2 degrees of positive overlap so the vacuum still will remain at 16 to 17 inches, but with the lobe separation angle being a 107 degrees, the throttle response will improve, and the car will come off the turn quicker. The driver should like the improved driveability.


Here’s a real rule bender – install Crane “Hi-Intensity” (Fast Bleed) hydraulic lifters and the vacuum at idle will go up by 2 to 3 inches. With these fast bleed lifters, you can push the envelope a little further camshaft-wise and still pass inspection.
 

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From http://www.se-r.net/about/200sx/scc/april98/april.html

One nice thing about twin cam engines is that since the intake and exhaust cams are separate, they can be adjusted independently of each other. This also allows adjustments to the lobe separation angle or overlap of the cams. Generally, if the cam lobes are moved closer together, the engines idle quality is reduced because the amount of overlap is increased. More overlap means that both the intake and exhaust valve are held open at the same time for more degrees of crank rotation causing intake charge dilution, cylinder pressure bleed down and reversion (intake port backflow) at low rpm.

Then there is the eight-stroke misfire phenomena that we previously wrote about (see July '97 SCC). Eight-stroking is what gives high-performance cams that traditional rumpity rump idle. More overlap also produces more low-mid range power, less right off of idle power and less top end power. More overlap also reduces an engine's octane demand as plenty of overlap reduces cylinder pressure right off of idle and at low rpm, which is the place where engines are the most prone to detonation.

OBDII controlled engines do not like lots of cam overlap because the irregular idle is picked up as a misfire event, triggering a MIL light and storing error codes. With the new California Smog II laws, you may have to report to a government controlled smog station which might not allow you to register your vehicle if you have stored error codes in your ECU or an enabled MIL light. Needless to say, keeping the OBDII system happy gets more and more important all the time.

Less overlap generally gives a smoother idle and, if the engine has sufficient breathing capability, more top end power at the expense of mid range. Of course, there are many "ifs" attached to any discussion of cam timing. If the engine has restrictive intake and exhaust systems, or if it has short connecting rods, or if it has an oversquared bore/stroke relationship (bigger bore than stroke), the engine will tend to lose top end power with less overlap. But most modern, four-valve-per-cylinder engines, especially when modified, will gain top end to some degree. Due to the lack of low-rpm eight-stroke misfire, less overlap also helps reduce hydrocarbon emissions. Usually, stock cams are ground with minimal overlap or even sometimes no overlap for this reason. This is usually too little overlap for good breathing. That is why sometimes large gains can be found with stock cams (especially Honda/Acura VTEC engines) with adjustable timing gears. Many aftermarket cam makers will grind their more radical profiles on the stock lobe centers. The stock lobe spread is often too separated for these cam profiles to work well. Adjustable timing gears allow for the correction of this and hence a large gain in power.
 

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Discussion Starter #11 (Edited)
Well I guess like most things in life they can be a little confusing at times. The info you posted said the tighter lobe center cam should have better driveability while the wider lobe center cam will have higher vacumm (of course the extra overlap it has may cause it to not have better vacuum I would suspect)

BUT since the numbers I came up with for the two cams show the 112° cam making more HP/torque throughout the entire rpm range would that not be the more drivable motor? I mean more torque at 2000rpm could only be a good thing right? Its not that the difference is very large it just surprised me that there was a difference at all and I'm trying to figure out what causes it and which of the two would be a better cam to have.

Anyway here is the numbers I got for the two cams....

This is the 106° cam
 

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Discussion Starter #12 (Edited)
And here is the 112° cam. Note that the vol. eff. is also higher for this cam then the 106° cam. Would that potentially indicate the car would/might get somewhat better MPG with the 112° cam?
 

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From: http://www.nastyz28.com/perftune.html#camshaft


Lobe Separation Angle: This is the relationship between the centerlines of the intake and exhaust lobes. A 110-degree lobe separation angle means that the peak opening points of the intake and exhaust lobes are 110 degrees apart. This is ground into the cam and can't be changed without changing cams. Lobe separation angle is another way of expressing overlap, which is the term formerly used by cam manufacturers. Overlap is the amount of time that both valves are open in the same cylinder When both valves are open at the same time, cylinder pressure drops. A cam with 106 degrees of lobe separation angle will have more overlap and a rougher idle than one with 112 degrees, but it'll usually make more midrange power.

From: http://www.vincihighperformance.com/LS1 TECH AND TUNE PAGE .HTML

Lobe Separation - Lobe separation is the distance in camshaft degrees that the intake and exhaust lobe centerlines are spread apart. This separation determines how peak torque will occur within the engine’s RPM and power range. Tight lobe separations, such as 108° or shorter, will cause the peak torque to build earlier in the RPM range and peak-out in a short amount of time. Broader lobe separations, such as 112°, will start making that torque peak later in the RPM range, but this allows the torque to build over a wider RPM range. Broader separation angles produce increased idle vacuum for more stable, cleaner, idles and better low end performance. They allow for easier tuning, as well.

From: http://www.classicfirebird.com/hand/jhand5.html

Lobe separation angle (LSA) directly affects valve overlap. As the LSA is decreased (called a "tighter" LSA), the overlap increases. An LSA of 108° is considered tight; 115.5° is considered wide. Tighter LSAs may produce more peak torque, but will yield poorer idle characteristics.

A tighter LSA will also move the power range down in rpm and peak the power in a narrower range. Wider LSAs allow the engine to idle better, produce more manifold vacuum at both idle and cruise, give better fuel economy, and produce a wider power band. However, a wider LSA also slightly reduces cylinder pressure, and consequently the engine may produce less peak torque. Since Pontiacs were fairly heavy cars and most were delivered with automatic transmissions, adequate lower-rpm response and a wider power band were considered more important than peak torque. Therefore Pontiac used wide LSAs on all factory cams. Also, remember that peak horsepower occurs for only a very short time in the upper rpm range, and it has very little effect on the overall performance of a vehicle that uses the total rpm range, from idle up. However, peak horsepower is important for a race engine that is operated in a narrow rpm range that's close to the peak horsepower point.
 

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From: http://www.newcovenant.com/speedcrafter/Engine/Camshaft/CamshaftBasics/tabid/144/Default.aspx


Lobe Center Angle is the distance in degrees between the centers of the lobes on the camshaft.
To increase duration, cam makers grind the lobes wider on the base circle of the cam. This makes the lobes overlap each other more, increasing overlap. More duration = more overlap.
To increase overlap without changing duration, cam makers will grind the lobes closer together, making a smaller lobe center angle. Less lobe center angle = more overlap.

Overlap and duration are the two big factors in cam design. More overlap moves the power band up in the engine's RPM range.
Longer duration keeps the valves open longer, so more air/fuel or exhaust can flow at higher speeds. It works out that increasing the duration of the camshaft by 10 degrees moves the engine's power band up by about 500 rpm.
A smaller lobe separation increases overlap, so a smaller lobe separation angle causes the engine's torque to peak early in the power band. Torque builds rapidly, peaks out, then falls off quickly. More lobe separation causes torque to build more slowly and peak later, but it is spread more evenly over the power band. So a larger lobe separation angle creates a flatter torque curve.
So you can see how a cam maker can tailor the camshaft specs to produce a particular power band in an engine--

* Short duration with a wide separation angle might be best for towing, producing a strong, smooth low-end torque curve.
* Long duration with a short separation angle might be suited for high-rpm drag racing, with a high-end, sharp torque peak.
* Moderate duration with wide separation angle might be best suited for an all-around street performance engine, producing a longer, smoother torque band that can still breathe well at higher RPM.
 

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From: http://chevyhiperformance.com/techarticles/95298/

In the early days of high- performance engine building, hot rodders discovered that when they squeezed the intake and the exhaust lobes closer together, the engine responded with more power. That experimentation continues to this day as engine builders struggle with the relationship between overlap and power.

Before we dive deeply into this subject, we should first define the term. Overlap is the number of crankshaft degrees that both the intake and exhaust valves are open as the cylinder transitions through the end of the exhaust stroke and into the intake stroke. The easiest way to understand overlap is by graphing the two lobes (see graph A) and examining the triangle created by the overlap of the intake opening (IO) and the exhaust closing (EC) points. This triangle is measured in degrees based on tappet checking height. This area is also referred to as the lobe separation angle—expressed as the spread in camshaft degrees between the intake centerline and the exhaust centerline.

This area is worth exploring because it is so complex. Let’s start with short-duration cams, which offer less overlap than long-duration cams even when they have the same lobe separation angle. Stated another way, a cam with more advertised duration is guaranteed to have more overlap than a cam with less advertised duration even with the same lobe separation angle. It’s also important to remember that overlap is ground into the camshaft when it is machined and cannot be changed without grinding a new camshaft unless you have a dual overhead cam engine with separate intake and exhaust cams.

Let’s look at a cam with an intake lobe centerline of 106 degrees after top dead center (ATDC) and an exhaust lobe with a 118-degree centerline before top dead center (BTDC). Adding the two values together and dividing by two equals 112 degrees. This is the lobe separation angle. While this number is useful, it doesn’t tell us much about the actual overlap between the intake and exhaust lobes. In order to calculate the actual overlap in crankshaft degrees, we need >> the intake opening (IO) and exhaust closing (EC) points. The SAE spec for advertised duration is 0.006 inch. Keep in mind that all cam companies do not use this spec. Let’s take a hydraulic-roller cam with an advertised duration of 276/282 degrees. The IO is 32 degrees BTDC and the EC is 27 degrees ATDC. Add these two values and we come up with 59 degrees of valve overlap.

Now let’s take a second, longer-duration cam with advertised duration figures of 294/300 degrees with an IO of 41 degrees BTDC and an EC of 36 degrees ATDC. We did the math and came up with a much larger figure of 77 degrees even though the lobe separation angle remains at 110 degrees. See how that works? This also illustrates why long-duration camshafts have such a lopey idle with very low idle vacuum. It’s not the duration itself, but the number of crankshaft degrees of engine rotation where both the intake and exhaust valves are open at the same time. At idle, there is plenty of time for residual exhaust gas in the combustion chamber to enter the intake manifold when the intake valve opens 41 degrees BTDC. This dilution of the intake manifold with exhaust gas is much like built-in exhaust gas recirculation (EGR) and is the culprit responsible for the unstable idle.

An unfortunate result of excessive overlap is reduced torque and soft throttle response at low engine speeds (e.g., below 3,000 rpm). So why build in all this overlap? The answer can be found when you look into the time that is compressed at high engine speed. At idle, there is plenty of time for the exhaust gas to move back up the intake tract and dilute the incoming charge. The intake air charge is also moving at a very slow speed. But buzz the engine to 6,000 rpm and there is precious little time for the exhaust gas to do anything except exit past the exhaust valve. Add the inertia of high-speed air entering the cylinder when the intake valve opens, and overlap is very useful for initiating that column of air into the cylinder. That 41 degrees BTDC intake opening point now works well to fill the cylinder with a big charge of air and fuel that now makes great power at 6,000 rpm. In effect, that early intake opening point gives the intake system a head start to fill the cylinder at high rpm when there is very little time. The result is more power at these higher engine speeds.

The difficulty with overlap is that the results change with different engine speeds. Since race engines tend to operate in relatively narrow rpm bands (e.g., 5,000 to 7,500 rpm), it’s easier to design a cam to work in this rpm band. A street engine is a greater challenge because it must operate through a rpm band of 5,000 rpm or more (1,000 to 6,000 rpm). The key to making overlap work is maximizing the power in the rpm band where you want it. Long overlap periods work best for high-rpm power. For the street, a long overlap period combined with long-duration profiles combine to kill low-speed torque. This makes for a soggy street engine at low engine speeds. Reducing overlap on a long-duration cam will often increase midrange torque at the expense of peak power, but if the average torque improves, that’s probably a change worth making.

The most important point in the four-stroke cycle is the intake closing point. While this is not part of overlap, the timing of intake opening and closing determines total duration. The intake closing point is a big determiner in where the engine makes power. A later intake closing point improves top-end power. Combine that with more overlap and you have a cam designed to make power at high rpm. However, it’s possible to decrease overlap by using a shorter-duration intake lobe and retard the intake centerline (which spreads the lobe separation angle) to improve midrange power.

We should also look at cams with a short duration and a wide lobe separation angle. All late-model Chevrolet engines use extremely wide lobe separation angles to improve idle quality. A late intake centerline combined with an early exhaust centerline and short-duration lobes creates very little overlap, yet the new LS1 and LS6 Gen III engines make great overall power without having to rely on large overlap periods. This is something to think about.

We would be remiss in not mentioning that many enthusiasts purchase a camshaft strictly on the basis of how it sounds. A cam with generous overlap creates that distinctive choppy idle that just sounds cool. There is a possibility that decreased overlap combined with an idealized intake closing point would create more power while producing a more stable (less lumpy) idle quality. This may not produce the idle sound most enthusiasts want to hear, but it is intriguing nonetheless.

There’s a ton more to learn about overlap and lobe separation angles than we can really get into in this short amount of space. It’s a relatively complex subject with many different conflicting requirements. But the more you learn about camshafts and how they operate, the more power you can make from your street engine.

See also:

http://chevyhiperformance.com/techarticles/95298/index1.html

http://chevyhiperformance.com/techarticles/95298/index2.html
 
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