I am begining to plan my next engine, most things are pretty much figured out except that elusive camshaft. I am not concerned with the duration yet because I am not sure how many cubes I am going to go with. So my question is, if you were to take two identical cams (same lift and duration) but changed the LSA from a 110 to a 106, what would happen to the power/torque output and the RPM operating range? This is going to be in a bracket car so things like power brakes are not an issue.

Hi JRausch

VARYING LOBE SEPARATION ANGLE

Tighten :

Moves Torque to Lower RPM
Increases Maximum Torque
Narrow Powerband
Builds Higher Cylinder Pressure
Increase Chance of Engine Knock
Increase Cranking Compression
Increase Effective Compression
Idle Vacuum is Reduced
Idle Quality Suffers
Open Valve-Overlap Increases
Closed Valve-Overlap Increases
Natural EGR Effect Increases
Decreases Piston-to-Valve Clearance

Widen :

Raise Torque to Higher RPM
Reduces Maximum Torque
Broadens Power Band
Reduce Maximum Cylinder Pressure
Decrease Chance of Engine Knock
Decrease Cranking Compression
Decrease Effective Compression
Idle Vacuum is Increased
Idle Quality Improves
Open Valve-Overlap Decreases
Closed Valve-Overlap Decreases
Natural EGR Effect is Reduced
Increases Piston-to-Valve Clearance

LOBE SEPARATION ANGLE

Above 114 Deg. = Extremely Wide
114-112 Deg. = Wide
112-110 Deg. = Moderately Wide
110-108 Deg. = Moderate
108-106 Deg. = Moderately Tight
106-104 Deg. = Tight
Below 104 Deg. = Extremely Tight


I hope that answers your question ;)

Hi JRausch

VARYING LOBE SEPARATION ANGLE

Tighten :

Moves Torque to Lower RPM
Increases Maximum Torque
Narrow Powerband
Builds Higher Cylinder Pressure
Increase Chance of Engine Knock
Increase Cranking Compression
Increase Effective Compression
Idle Vacuum is Reduced
Idle Quality Suffers
Open Valve-Overlap Increases
Closed Valve-Overlap Increases
Natural EGR Effect Increases
Decreases Piston-to-Valve Clearance

Widen :

Raise Torque to Higher RPM
Reduces Maximum Torque
Broadens Power Band
Reduce Maximum Cylinder Pressure
Decrease Chance of Engine Knock
Decrease Cranking Compression
Decrease Effective Compression
Idle Vacuum is Increased
Idle Quality Improves
Open Valve-Overlap Decreases
Closed Valve-Overlap Decreases
Natural EGR Effect is Reduced
Increases Piston-to-Valve Clearance

LOBE SEPARATION ANGLE

Above 114 Deg. = Extremely Wide
114-112 Deg. = Wide
112-110 Deg. = Moderately Wide
110-108 Deg. = Moderate
108-106 Deg. = Moderately Tight
106-104 Deg. = Tight
Below 104 Deg. = Extremely Tight


I hope that answers your question ;)


Useful and interesting...............I'm sure its appreciated

IMHO, cam design is like porting... to paraphrase Smokey Yunich "if you don't do it for a living, leave it to someone who does". You shouldn't be looking at what the lsa does to or for you, you should have the valve events designed to accomplish your goals and let the lsa fall where it may.

My suggestion would be to contact Jay Allen at Camshaft Innovations (http://www.camshaftinnovations.com/).

The camshaft is the 2nd to the last thing to be purchased, last is pushrods. Don't put the cart before the horse. Untill you have cylinder heads, CID, rod length, carb cfm, and desired power range there is no way in hell to select a camshaft based on LSA. Case in point, 355CID circle track engine with an LSA of 107 has a max HP of 631HP and peak torque of 520#/ft and holds with in 7% of peak for 2400 rpm. This is not considered a narrow powerband by any means.

I am obviously going to pick a cam that works in conjunction with all the rest of the parts. I was just wondering what would happen in this case to help aid in my desision, what ever it is. Is there any kind of guideline that someone could follow. Like every 2 degrees narrower on the LSA the RPM band will be shortened by so many RPM's? Maybe, I am asking too much?

Maybe, I am asking too much?

Yes you are. There is no fixed variation in performance for each amount of change in some cam parameter. There are many other factors involved.

I kind of suspected that, I was just wondering. Thanks>

I am obviously going to pick a cam that works in conjunction with all the rest of the parts. I was just wondering what would happen in this case to help aid in my desision, what ever it is. Is there any kind of guideline that someone could follow. Like every 2 degrees narrower on the LSA the RPM band will be shortened by so many RPM's? Maybe, I am asking too much?

The truth, No. Unless you build the exact combination that someone has proven dyno and end results with there are just to many variables. Ask questions, get a game plan, round up parts, then worry about the cam. Believe me you will save yourself some grief.

I am obviously going to pick a cam that works in conjunction with all the rest of the parts. I was just wondering what would happen in this case to help aid in my desision, what ever it is. Is there any kind of guideline that someone could follow. Like every 2 degrees narrower on the LSA the RPM band will be shortened by so many RPM's? Maybe, I am asking too much?
No you are not asking too much in that as long as you have specified all of the parameters of the application the cam designers can put you pretty close in the game.............all you need to do is select the right resources for ( intelligent) info. Do not....repeat do not ever call a cam hotline and expect a wealth of knowledge to come from the other end. You discuss your combo with seasoned engine builders ( not assemblers ) and engineers at cam companys and collect info that is consistant...............and that is the KEY.......consistantly similar answers. They may give you a range of lobes or lobe centers ( separation ) that may work, sometimes its trial and error within this window until you find the sweet spot..........make your phone calls.........Chris Padgett @comp, Darin Morgan @ Reher - Morrison just to name a few........there's plenty out there...............hell what about Mike @ wolfsplace and on and on.........look for generalizations in applications like yours...........right!

Bracket car only? Not Street-n-Strip? Automatic?
For either 355 or 406, 90% on the time---106 LSA, either solid lifter or roller cam.
LSAs like 110 are for Street-n-Strip cars, heavy on the Street, or else very light Econo-Dragster types with 7000 SS converters.
A LSA of 106 covers everything from 11 seconds down to 8 seconds.

UDHarold

Harold...

Thanks for your reply. The engine I am planning to build is a 406-421 sbc with approx. 11.5:1 comp, sportman II ported heads, victor jr. intake,
1 3/4 headers with a max of 6500-7000 RPM and was going with a solid lifter cam. The car is 3500 lbs bracket car only, TH 350 with 3500 stall, and 4.10 gears. Any recomendations for a cam would be very helpful. My goal is to end up running 11.3-11.6 at an altitude of 2200+ feet.

JRausch,

Any kin to Jack? We used to work together--Cam desiginer to Racer--back in the mid 1970s......
For that size engine, car weight, converter & rear, and altitude, I'd use a Lunati 401B4LUN, or a Bullet/UltraDyne UF71/UF75-106. That cam's specs are 283/291 @ .020, 255/263 @ .050, .550"/.570" gross valve lift, and 106 LSA. If you use a 1.6:1 on the intake, the lift is .587". With lash and deflection, you're looking at about .570"/.550" net lift. Obviously, this cam will require a good fuel system, minimum being a high-volume Carter or Holley mech pump, and 1/2" fuel lines.
You will also need a small-base-circle version of this cam, and the 421 will require a smaller base circle than the 406. Make sure you tell them your stroke when you buy.
The car weight, converter and rear gear, and altitude works against a larger solid lifter cam. A roller cam would add about .100" net valve lift, and at least an additional $750 cost above the solid cam.

UDHarold

Harold....
I can't find the specs on the UF71/UF75-106 that you had recomended on their web site. I am curious what the cam is like. Thanks for your help.

Those are the same specs, and the same cam, as the Lunati 401B4LUN. Both companies have my masters, and make the same cam, they just call it different names. The UF71/UF75 is the name I called it at UltraDyne.
Bullet does not list any of the UltraDyne cams. Go to Wayback Machine--Look it up in Google--and enter www.ultradyne.com. If you just enter the ultradyne in Google, it takes you to Bullet's web site, and no info. Wayback Machine takes you back to 1999-2003 and shows you what my old web site looked like.....

UDHarold

Car craft magazine had a dyno test on just this topic about 18 months ago, tested 3 cams with same duration and lift with different LSA. Dave.

Car craft magazine had a dyno test on just this topic about 18 months ago, tested 3 cams with same duration and lift with different LSA. Dave.


Link?? :)

Car craft magazine had a dyno test on just this topic about 18 months ago, tested 3 cams with same duration and lift with different LSA. Dave.



Dave how would I find this info, I am really curious to see what it has to say.

I'm going out on a limb here but hell I have before. Unless you are going to build an EACXT engine combination and run the EXACT engine rpm range as the engine combination, selecting a camshaft based on LSA is boggus.

What does a cam do? It opens and closes valves.

What is an engine? It is an air pump.

Based on the needs of a given displacement running at a given rpm one can calculate the air needed to fill the displacement for max efficency. Know this one can then test the induction system and exhaust systems ability to move air. . .their capabilities. Once this is known the valve path that is needed can be determined by selecting a lobe that has both the time of duration and rate of lift needed to create the valve path to allow air and fuel in and out. This valve path has an opening and a closing referred to as valve events.

Based on the capabilties of the induction and exhaust system to fill and exit these opening and closings will vary with every engine and through out a given rpm range. A given engine with fast flowing heads in low to mid lift numbers will have a LSA much different then the same engine with heads with poor flowing low and mid lift numbers.

Then in our pushrod V-8s any give LSA is a compromise because as rpm changes the required valve events to fill the "air pump" change also. Hence the reason those V-Tec's run so well with variable valve timing.

Bottom line you correctly cam an engine based on combination and rpm goal it will run, it will make power.

Jrausch in no means am I belittling your though process I just care about what I do, the industry I am in, and I don't want you to make a mistake. So please just take this as advice and not a flame or dig.

I am not choosing a camshaft purely based on LSA, I know there are many factors that come in to play when picking an cam. I am just curious what affect it has on the engine, and if there is any research done on the subject I would like to read it to further my understanding and with this knowlege hopefully it will help me make the right decision.

Good flowing heads, matched cross section to fill CID at desired rpm= Moderate LSA
Super flowing heads, over kill on cross section to fill CID to desired rpm=
Wide LSA
Poor flowing heads, matched cross section to fill CID to desired rpm=
Moderate LSA

Poor flowing heads, inadequate cross section to fill CID to desired rpm=
Tight LSA

It all varies with what you have and what you want to do. Above is basic guide line I can give you but even that can vary. I have a good customer in Edmonton, Pro Stock Performance. I would get get your combination together with choices in heads, intake, CID, Carb and all that stuff then base the cam off of what you have and what you want to achieve.