Camshaft lobe separation angle: what does it mean?

Camshaft lobe separation angle: what does it mean?

By Freddie Heaney:

The lobe separation angle of a camshaft is typically determined by the engine’s purpose, its displacement, and its compression ratio.

A 350cu in oval track racing engine, for example, often runs on a narrow lobe separation angle of 106 degrees. In contrast, a smooth-running high-performance street engine might use a lobe separation angle of 112 to 114 degrees. Five-hundred cubic inch NHRA Pro Stock engines in 2015 that revved to 11,000rpm operated on 116 degrees LSA and 800-plus cu in Pro Stock Mountain Motors 120 to 122.

The lobe separation angle or LSA is the angle in camshaft degrees between the maximum lift points, or centerlines, of the intake and exhaust lobes.

The lobe separation angle or LSA is the angle in camshaft degrees between the maximum lift points, or centerlines, of the intake and exhaust lobes.

 

The lobe separation angle is the angle in camshaft degrees between the maximum lift points, or centerlines, of the intake and exhaust lobes. It affects the amount of valve overlap; that is the brief period of time when both the intake and exhaust valves are open.

A narrower LSA adopts more overlap and with it a lumpier idle and a narrower more specific power band. The narrower separation makes the engine sound choppier. Some engine specialists refer to it as that 106 sound—the NASCAR and short track oval sound where preferred lobe separation is usually specified between 104 and 106 degrees. The primary function of narrow lobe separation is to impel urgent acceleration off the turns when the throttle is opened.

A wider LSA, on the other hand, reduces valve overlap, offering better idle and cruising qualities. Supercharged engines typically benefit from a wider LSA because they don’t require as much overlap for exhaust scavenging as does the naturally aspirated engine.

Doug Patton, Pro Line Racing Engines

Doug Patton, Pro Line Racing Engines

“Changing the lobe separation angle,” says Doug Patton of Pro Line Race Engines, “changes the amount of overlap that exists during the time the intake and exhaust valves are both open. On a naturally aspirated engine, the lobe separation angle has an effect on whether the engine reaches peak torque a little earlier or later in the rpm range. Typically, narrower lobe separation develops peak torque at lower rpm and widening the separation tends to build peak torque higher in the rpm range. Nitrous engines, which make plenty of power and torque, often run wide lobe separation angles to moderate cylinder pressures and temperatures.

“Lobe separation angles,” he continues, “are influenced by the camshaft grind. If a street car has smaller lift (the amount the valve lifts off its seat) and duration numbers (the degrees of crankshaft rotation for which the valve is held open) they might run 112 or 114. Widening their separation angle helps increase upper rpm power output. Alternatively, if you are running a bigger camshaft to gain maximum top-end power, cam makers often suggest reducing the lobe separation angle to recover power lost in the lower rev range.”

Chuck Lawrence, Jon Kaase Racing Engines

Chuck Lawrence, Jon Kaase Racing Engines

Tellingly, when engine builder Chuck Lawrence received the order to bestow a 520cu in big-block Ford with the sound of a Pro Stock engine, he replaced the normal 112LSA hydraulic roller cam with one of 108LSA. “The result sounded wonderful,” said Lawrence, “but it didn’t rev as enthusiastically and it made 30hp less than normal!”

“If you changed the lobe separation of a street engine from 112 degrees to 106 and didn’t do anything else,” says Jon Kaase, “the engine would idle a lot rougher and generate worse exhaust emissions largely because of unburned fuel.”

In conclusion, lobe separation angles change the amount of valve overlap, which affects many performance factors particularly idle quality, peak torque that can be moved from a lower rev range to a higher range and power bands that can be narrowed or broadened.

Narrow Angle (104 degrees) means:

  • Lower rpm torque range
  • Increases maximum torque
  • Higher cylinder pressure
  • Lower idle vacuum
  • Rough idle quality
  • Valve overlap increases

Wide Angle (115 degrees) means:

  • Higher rpm torque range
  • Decreases max torque
  • Lower cylinder pressure
  • Higher idle vacuum
  • Smooth idle quality
  • Valve overlap decreases

Source:

John Hartman (Jhartman@PBM-ERSON.com)

Erson Cams
800-641-7920
www.pbm-erson.com

8 Comments

  1. I have taken a look at this topic on LSA and I want to know more and hope to benefit from you

    Reply
    • I have a Howard’s small base circle hydraulic roller camshaft. I understand all the numbers except the L/C. It is 110+4. What exactly does that mean? Your input would be greatly appreciated. Thanks in advance, Randy Graves

      Reply
      • Randy,

        Regarding your question, I called Kaase this morning on his way to work, as he’s inclined to leave his phone in his truck during the day. So, here below is his reply. Trusting my shorthand is accurate and not too rusty.

        “A lobe separation angle of 110 degrees plus 4 between the intake and exhaust lobes means the camshaft is ground with four degrees of advance. This means when you install the camshaft with a set of stock gears, its timing will be advanced by four degrees, assuming everything else is perfect.

        “The effect of four degrees of advanced timing would cause the intake valve to close sooner and trap a little more compression. At low speed the engine will have a little more giddy-up. But if you favor slightly more power at high revs, you’d probably prefer the intake valve to close marginally later because the cylinder is still filling when it closes, mainly due to inertia. However, most engines seem to perform slightly better with the cam advanced by 2 or 4 degrees and having it ground in this way saves the purchase of an adjustable timing set.

        “Randy’s question is understandable because the effects of differing lobe separation angles are not immediately obvious. As the lobe angles are fixed, unless you’re running overhead camshafts where you can adjust them independently, your decision on selecting a specific separation angle should include determining the engine’s main purpose, its stroke length, how much vacuum it needs, and so on. Hope this helps.”

        Reply
  2. To Bahloooq, thank you for your note. Could you tell us more specifically the information you’d like to receive. Failing this, please contact John Hartman by email: Jhartman@PBM-ERSON.com

    Reply
  3. My problem is raw fuel going off like a bomb on deceleration.

    This occurs on my recently built 496 BBC stroker. It has big port raised-exhaust port heads and squared, 0.005 in the hole with Wiesco +0.020 dome pistons. The static compression ratio seems to be around 11:1. It produces 180 psi when closing all cylinders. It has 7 inches of vacuum with a Lunati hydraulic roller cam that lifts 0.629-629 with duration of 250 in, 255 ex., 110 centerline and 112 LSA.

    Originally, on startup I ran gasoline 93 and a Barry Grant 850cfm with no problem but the carb was noticeably small for this engine. So, I decided to go E-85 with a new 950 Holley E-85 carb, which is when trouble struck. Assuming it was a jetting issue, I spent much time with Holley “techs”. But after tuning this carb from a-z there was no change and I’ve come to the conclusion it is not a carb issue. The car pulls hard to 7000rpm but whether coming off full throttle or just granny shifting, I get this back-blast in the headers. Do you think it could be scavenging or cam timing or wrong cam? I’ve replaced the wires, 6AL box, and re-degreed the cam. I’d be grateful for your help. Thank you, Tom Muzik

    Reply
  4. A lot of street racers like to fit a big cam in their engines because it sounds good, even in a stock engine like a 1968-’70 327cid Chevrolet, which has 275-300hp. However, without changing anything else, you’ll lose horsepower – vacuum secondaries won’t open, too much overlap in 108 LSA or below. If you don’t go all the way – compression ratio, larger valves in heads, headers, high-rise alum, mechanical secondaries Holley carburetor, balanced engine, 3in exhaust etc., – don’t start, for it will be a waste of money.

    Reply
  5. I have a Pontiac 350. I am unfamiliar with these engines, and I’m told they react differently than the SBC. My engine, apparently, has a decent cam in it with a narrow lobe separation angle, because I am only pulling 7-1/2 in of vacuum. I am not a drag racer. However, I enjoy more mid- to upper-range power. I am running a FAST 2.0 EFI, which requires a minimum of 10in of manifold vacuum. What would be my narrowest lobe-separation angle to achieve 10in of vacuum?

    Reply
  6. Having only 7.5in of manifold vacuum probably indicates your cam is very big or you have a vacuum leak. Often, street cars have vacuum hoses connected to numerous accessories, even the heater box.

    Without knowing the cam duration at 0.050in., most engine builders could not advise you further. Camshaft duration is the measurement of the time one valve begins to open until it finishes closing, and it is measured in degrees of crankshaft rotation, not camshaft rotation. If it is 260 degrees @ 0.050in on both intake and exhaust and with 114 LSA, it would probably generate sufficient vacuum. But if you have a large camshaft with 106 LSA, it might generate the little vacuum you describe. If this is the case, you’ll have to change the camshaft. Compare two camshafts, one with 240 degrees @ 0.50in the other 260 degrees @ 0.050in and both with the same LSA, the one with the greater degrees of duration will display less vacuum.

    If your fuel injection system is satisfactory and the engine functions well enough, it may not be in your interest to change the camshaft. But with insufficient vacuum, some EFI systems are inadequate. If it is port injection with the injectors located on each port down by the valve covers, the fuel distribution will be acceptable. The most intractable problem occurs with throttle body injection systems, blowing raw fuel where the carburetor would be. That said, the Holley Sniper appears to be a completely other creature. From our consensus, the reflections of half a dozen leading engine builders, it is superior to all others of this kind.

    One final point, most of the time enthusiasts are not at fully open throttle, unless during track racing or in a boat. Few of us exceed 3,000 or 3,500rpm in street cars. Thus, it is almost irrelevant whether your engine generates 400 or 600hp. What’s important is the available power between 1,800 to 3,500rpm. Generally, when you increase camshaft size, it harms power output in this range.

    Reply

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