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 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.
“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.”
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
John Hartman (Jhartman@PBM-ERSON.com)
I have taken a look at this topic on LSA and I want to know more and hope to benefit from you
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
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.”
Why does the 350 Chevy crate racing engine have a 112LSA on hydraulic rollers
I do not fully understand your question so I will provide a broad-based response. If you can further define your question I will be happy to offer my best explanation.
A camshaft profile is considered a polynomial curve and the lobe profile is designed from the maximum lift point. Since the valves in the cylinder head are nothing more than doors that allow charge to enter and exit the bore, the lobe of the camshaft (its ramp) is employed to control when (in terms of crankshaft degrees) the doors open, how quickly in rotational degrees they open, how high they open, how long they dwell open, when they start to close, and the time both doors are open (overlap which is read in part as LSA).
Many years back I wrote an article for HOT ROD magazine on using the Audie Technologies Cam Pro Plus. It is a camshaft inspection tool that plots all aspects of the cam lobe design. You may be able to find it on the internet. The reason I reference this text to you is due to the fact that camshaft inspection equipment visually shows the often hard to imagine dynamics of the lobe shape.https://www.motortrend.com/how-to/0308pon-pontiac-camshafts/
With regard to the hydraulic roller lifter, the roller allows for a more aggressive ramp (quicker rate of valve opening or closing) since it can follow the contour more accurately.
More torque from a wider LSA? No, except on a supercharged engine. There’s plenty of research showing the contrary. Narrow LSAs increase torque by a minimum of 30 pounds-feet through the entire range, which when you consider average torque and horsepower makes a huge difference.
Received from R.T. Bohacz in response to Chris:
I’ve been around engines my entire life, and I found this article on LSA to be well written and extremely accurate. Yet, I do find truth in what Chris is stating. I will explain.
As the article stated (in general terms) a wider LSA (higher numerically) is beneficial to both naturally aspirated and forced induction engines (since the boost is less likely to be blown out the exhaust valve). The stumbling block being that the text is covering the topic in general terms. Less overlap equates to more torque in almost every situation. But as with everything there are exceptions.
For example, if you take two engines of the same displacement and specifications, one is going to be in a drag car and the other in a truck that tows a trailer. The camshaft with less overlap will produce more torque at a lower engine speed than one with more overlap. Will the engine possibly produce more power with the aggressive cam profile at higher rpm? There is an excellent probability it would. Where the power comes in at would not do the truck driver any good pulling a heavy load from a stop on a hill.
The same engine now in a drag race car with a loose torque converter and a high numerical axle ratio would be able to enjoy the higher cylinder fill the overlap provided since it is operating at a higher engine speed.
It would be almost impossible to state that a minimum increase of 30 pounds feet are a rule. What comes to mind is a SBC with a long runner TPI manifold and two cams, one with more overlap and the other with less. In that application, the overlap will fight the long runner manifold design and also cause a high level of reversion back into the plenum, killing power.
In addition, most if not all race/modified engines when dyno tested are pulled from a high engine speed as a staring point. So, if the pull is from 4,000 rpm to 6,500 rpm, I can most certainly see an increase of torque throughout that speed range (area under that curve). But if you pull that engine down to 1,500rpm the story would be different.
Also keep in mind that the camshaft needs to work in harmony with all other aspects of the engine and is not a stand-alone entity. The camshaft is always a compromise unless it is fitted to a steady state engine such on an irrigation pump or even a lawn mower.
For this reason, modern engines are equipped with variable cam timing along with variable runner intake manifolds. Those two disciples when working together allow the best of all worlds.
I hope this clears things up.
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
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
Tom, did you resolve your raw fuel igniting on deceleration troubles? I’m curious as to the size of your header primaries? I have built numerous engines of your spec. I run 2.125″ internal diameter headers. I also run 950cfm HP Holley street and 1050cfm Dominator track. In your case, I suspect your headers may cause excessive backpressure. I think your cam spec is okay but I’d also recommend re-checking your timing marks and verifying their zero-at-TDC accuracy. Mismarked balancers are not unheard of. Cheers!
I’ve listed the cam specs below of my 1984 Corvette. As no one sells stock camshafts for it, the best I can find is a 112 LSA.
Before I learned about the vacuum qualities of lobe separation angles, I fitted a camshaft with less LSA, but the car idled terribly. There was insufficient vacuum to activate the brake booster. Given that the rest of the engine is in good condition, is there a way of determining vacuum by lobe separation angle? I read that brake boosters require at least 18 inches of vacuum to operate correctly.
This difficulty confounds me, especially since reprogramming the 1984 PROM is impossible, so the engine needs to be comparatively stock. It’s just this last part, then I’ll drive it a bit and sell it.
The cams specs for 1984 thru ’86 are as follows: Duration @ 0.050″, 202/206, Lift .403/.415, Lobe separation angle 115 degrees. Jun 11, 2002
Don’t be overly concerned. Most camshaft specialists will grind the profile you require. Call Russ Yoder of Erson (502) 216-8804(M). The cam duration you specify is tiny (202/206). I assume your engine to be small-block Chevrolet, so cam grinders should have easy access to an appropriate cam core.
I have a 396ci sbc with a solid roller cam that ran well but noisy and a little problematic. In 2018 it broke a rocker and more recently a valve spring.
I am ready to make a change in valve train and go hydraulic roller and EFI but want to make as much power as possible: 550-600hp (crank) on pump gas. Mostly street-driven, my car is a 1971 Camaro weighing 3,700lbs with driver, transmitting through a Tremec TKX 5spd manual, 3.73 gears and a 26in tall tire.
Current Lunati 40120733 cam specs are as follows:
Advertised duration (Int/Exh) 279/285; Duration @ .050 (Int/Exh) 249/255;
Gross Valve Lift (Int/Exh) 0.585/.600 (0.624Int. .640Exh. with 1.6 rocker);
Valve lash (Int/Exh) 016/016;
RPM range 2800-7200
Lunati recommends 200lbs seat and 600lbs over for valve springs
Approx. 10.75 compression ratio
Lunati 1.6 rockers
Brodix Track 1 heads ported 2.08 intake 1.60 exhaust valves
Edelbrock 2925 port-matched intake (Felpro 1206)
Pro Systems Holley 950HP carb
I would like to install the Edelbrock ProFlow 4 multiport fuel injection system, which requires at least 8″ of manifold vacuum.
Looking for recommendations
Probably it will, but there is more to it. The duration numbers and what type of induction will also be factors.
Since you know that big lopy cams and EFI do not work well, here are my three recommendations:
1.282/288 2.275/281 3.277/283
231/237 224/230 226/232
535/545 527/532 530/535
LSA114/ICL110 LSA117/ICL113 LSA116/ICL112
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.
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?
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.
I have a 1984 Chevrolet powered by a 350 small block. I’m converting to EFI via Holley Sniper and adding the Hyperspark system to provide timing control. The truck came with an Engine Pro camshaft MC1612. It is a heavy lobe cam with an LSA of 110 degrees, 254 @.050, 295 ave duration, and 0.485in valve lift. Lash is 0.030in.
I don’t know the manifold pressure but it isn’t much, as I was having vacuum problems. Will the Holley Sniper compensate for the cam or should I add something to boost the vacuum pressure?
Increasing numbers of engine builders will tell you that it might work but perhaps not. Entry-level EFIs (please forgive if this an impertinent term) can be troublesome with low vacuum at idle. Your present camshaft would likely perform better with a throttle body with port injectors situated down near the valve covers. On the other hand, if you wished to retain your EFI you may be obliged to change your camshaft – to decrease its specs.
I have a 406 small-block Chevrolet street/strip engine with 11:1cr and 6in rods, 3.75 stroke and 64cc 225 intake runners. The cam is a Howard’s solid roller 640/645 [valve lift presumably] with cam duration of 263 @ 0.050in intake and 273 exhaust and 106 degrees lobe separation angle (102C/L). My question is this, should I have selected a 110LSA instead? I’m confused! Have I chosen the right cam to facilitate a good-running engine? Please help. Robert
Given your engine size, your selection of 106 lobe separation angle is probably fine, and with what seems like Cup Car specifications, the engine will sound impressive.
I’m rebuilding a 305 SBC for my truck and seeking more torque. I’ve a dual-plane intake, headers, and 650cfm carburetor and everything else pretty much stock. I’m thinking of a cam with 204-208 duration at 0.050in and 420 to around .43x to .442 lift and around 112LSA, maintaining power range between 1000/1200 to 4800/5200. I may try a 2 degree advance. What do you think?
Yes RJ, those specs should work well for your purposes.
If I have a cam with 110lsa and I advance it by 6 degrees, will it have a more lumpy sound?
No it will not make the idle any different (lopy idle-wise), but it will raise your bottom-end power and you will lose some high RPM horsepower. Most cams have 4 degrees advance ground into them as this is a good compromise.
I have a roller cam that was ground based on the CS XS268S-10m with a baseline rpm of 1600 to 6000rpm.
This is a dirt track racing engine and my roller is pulling 19in of vacuum at 1,000rpm. The cam is 230-236 with 110 lobe separation angle and .490ish to .521in of lift. Other engine specs include World Product S/R heads, long tube headers, Edelbrock RPM Air Gap intake, and 10.25 to 1 compression. As I have tons of vacuum, and can’t be lower than 15, do you think it would be wise to drop it from a 110 to a 108LSA to create more lower punch and more mid-range punch and still be above 15in vacuum?
Hello Dirt Racer Class,
Did you mention the size of your engine? If not, you’re likely running a small-block although big-blocks are popular in the northeast. As your vacuum is considerable, you might be better advised to increase your camshaft specs before tightening lobe centers. If your intake and cylinder heads are performing well, your camshaft may be too small. Increasing its specs by 10 degrees (240-246) would probably be more advisable, and if the vacuum is still in abundance, you might consider a further increase in camshaft before changing LSA.
I have looked into this issue of LSA and would want to learn more about it. I am hoping to gain some insight from you.
I would like your recommendation for a hydraulic roller camshaft duration/lsa to produce approximately 350 -375 peak HP around 6000 rpm, at least 400lb-ft of peak torque and enough vacuum to run power accessories. My car’s stats are as follows: SBC 350, 600cfm carburetor, 64cc heads (1.94/1.50), curb weight of 4200lbs., 200-R4 transmission w/ 2000 stall, 3.73 rear end gears and 28″ wheels. Upgrades, in addition to the cam, will be an Air-Gap intake manifold, flat-top pistons and boring the block to 355cid.
If I have a 358ci making 605hp at 7,100rpm that incorporates a 263/273 113LSA with 0.720in lift, and I replaced it with a 260/266 104 LSA with 0.720in lift, what effect would it have? Would it change the sound drastically if tuned to suit and idle properly (high)?
Your question may have already been answered in the article or in the comments above, but if not here is a response from Chris Thomas of Kaase Racing Engines:-
“Replacing a 113 with a 104lsa is a drastic change. The 104 will sound very aggressive compared to the 113. Generally, I would not select such an narrow lobe separation angle, however, it is dependent on what Max is trying to do with his engine and his vehicle specifications also need consideration, such as weight, rear gear, tire size etc. If this vehicle is driven daily, I would not recommend the 104. On the other hand, if he is engaging in round track racing on a short track, the 104 would be more beneficial. Always select the camshaft for the engine purpose it has to serve.”
Great share! Thanks for the information. Keep going!
Related to Street Stock circle track racing, my engine is a 350 SBC with flat top pistons, 72cc cylinder heads, 1.94in intake and 1.5in exhaust valves, stock rockers, 0.450in max lift on cam hydraulic flat tappet, and Edelbrock 2101 intake manifold with 500cfm Holley 4412 carburetor and competing in 3/8 mile mild-banked asphalt tracks. Please advise an effective cam design for a low-compression engine like this. I am more familiar with higher compression engines, and I’m having difficulty in finding a cam that pulls hard off the turns.
Your best approach is to contact a performance camshaft company; nonetheless, here is the opinion of one of our local engine builders:
“Initial thoughts would be something like 252/256 @ 0.050in on a 104 or 106LSA. Installed with the intake centerline of 100. He’s limited to a 0.300in lobe lift. Without knowing what he has already tried or further information about the car this is my best guess. I would run the hydraulic lifter like a solid, as in bottom the plunger in the lifter out with the valve adjustment to where he had about 0.015in or so travel in the lifter plunger.”
I have a 1982 Corvette with 700r transmission, 2.87 gears and ported Crossfire engine. The cam I’m looking at is a 209/215 .465/.470 112LSA and 108C/L. The engine details include a rebuilt stock 350 block, flat top pistons with valve relief of 0.05in. Do you think this combination will work with 180cc 70 camber heads and still achieve good low-end torque and vacuum?
Here is a response from our local engine-builder friend, Chris Thomas: “I would concur with Kevin’s choice and use the 112LSA as it will give more manifold vacuum, be less choppy at idle, and will still have ample lower-end torque. The duration seems appropriate for what he’s got.”