Optimum LCA
- Thread starter octanejunkie
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moper
Well-Known Member
I believe he is referring to the mechanics of the engine... Meaning for every given stroke and rod combination, there is a point where maximum force can be placed on the piston by the burn and make the most torque. And that relationship does not change unless you alter the stroke or rod length because it's the position of the piston and how the rod transfers torque to the crank. I'd add fuel type to the list of "must knows" to that too because the fuel burn time is critical to when max pressure is developed. The rest of the system can be altered by trying to take advantage of various other things but the perfect mechanical relationship is a constant.
Edit... as for figuring out which is the right one for a combo... I think Pipemax can do it. It's just equasions and some trig but I was never good at higher math.
Edit... as for figuring out which is the right one for a combo... I think Pipemax can do it. It's just equasions and some trig but I was never good at higher math.
Thanks!!!!! Grate article!
Can't really comment other then,.......what i think he is saying, is that every eng combo need a "X "lobe separation........and is figured by the right duration/overlap.....Which will Be "X" lobe seperation......................
Thank moper, much better description!!! ;-)
octanejunkie
Mopar Padawan
Found this on post by Grumpyvette on another site:
Lobe separation is the number of degrees that separate the peak lift points of the cams intake and exhaust lobe. Like duration, lobe separation helps determine the cams rpm range. Generally, a cam with wider lobe separation (112-116 degrees) will make power over a wider rpm band. A cam with narrow lobe separation (under 112 degrees) is biased toward peak power and operates within a narrower rpm band.For the street, you want a cam with a fairly wide lobe separation for the best power production over the engines entire rpm range. Go too narrow with lobe separation and you may end up with an engine with a peaky powerband biased to high rpm horsepowernot the hot ticket for a street car.
For my personal purposes, gasoline is the only fuel type I am considering at this time... but that is a good point.
It is a "big picture" thing, all elements considered, in my opinion - but I found the article interesting, especially the statement I quoted, hence this thread
moper
Well-Known Member
I dont know who Grumpyvette might be but from that snippet I'd say he and Vizard are not talking about the same thing. Vizard is saying that the perfect LCA will close the intake valve at such a time that maximum compression of the mixture will occur and as such with a given burn time the maximum force will be applied to the piston exacly at the moment it has the best mechanical advantage and thus get maximum torque.
Grumpy is looking with a larger magnifying glass and taking other variables into account and as soon as anything is compromised the "perfect number" starts to change as a result. To me, it's a little misleading. I'd boil it down to design an engine package understanding all the parts and how your choices affect getting that mix into the chamber, then cam accordingly, and you're good. Change something, or misunderstand one of the variables, or simply compromise for one of them, and that "good" gets lost.
Grumpy is looking with a larger magnifying glass and taking other variables into account and as soon as anything is compromised the "perfect number" starts to change as a result. To me, it's a little misleading. I'd boil it down to design an engine package understanding all the parts and how your choices affect getting that mix into the chamber, then cam accordingly, and you're good. Change something, or misunderstand one of the variables, or simply compromise for one of them, and that "good" gets lost.
moper
Well-Known Member
There's got to be some other opinions here... let's hear them.
octanejunkie
Mopar Padawan
Grumpyvette runs Grumpys Performance web site, but he is not only corvette-specific, the post I quoted is from a thread on this site which he apparently moderates along with at least one Chevy site I frequent as well. I PM'd him a question once with my phone number and he called me to chat, nice guy with a lot of experience to share. Yes he does advocate a "big "picture" approach to cam/component selection and engine spec per given task. The blurb I posted credited to him was a copy/paste from Summit's web site apparently.
I inherently understand what Vizard is saying but was most impressed by the statement "For a given spec of engine there is only one LCA that will give optimum torque and horsepower." Vizard goes on to say that for a street driven vehicle, erring on the wider side is safer than too narrow, in respect to low end torque and drive-ability while the opposite holds true for a race car; at least in respect to the LCA's effect on peak power output - which is essentially the same thing Grumpy's post indicates.
moper
Well-Known Member
I agree. I think Vizard is taking the scientists' view. Which is ultimately there is only one perfect mathematical LCA for a given engine. The problem I see (I take Grumpy's approach too BTW) is that in order to focus on that perfect point... you have to sacrifice worrying about things like packaging, parts availability, budget, and legal constraints.
octanejunkie
Mopar Padawan
Well, for our purposes, let's not constrain ourselves with the practical limitations of a manufacturer/vendor - if we had no limits and could spec/cut the perfect cam for our combo THEN how would we go about determining the correct LCA for an application; that in my opinion is the $64,000 question
Knowing that there are many pre-ground choices out there with almost every possible LCA, how do we determine what is the optimum for our applications?
Grumpy posted an LCA/LSA comparison thread, also a Vizard effort IIRC, in a thread on his site here, for those that are not members to GPG here is an exerpt, but the entire thread is well worth reading, at least 3x
What we begin to learn here is what we can and cannot influence beyond cam selection, meaning installation, or degree-ing a cam. Interesting note, almost overlooked here, LCA and LSA are NOT interchangeable terms.
lead69
hopeless car junkie
[/QUOTE] Interesting note, almost overlooked here, LCA and LSA are NOT interchangeable terms.[/QUOTE]
This is what confuses most people on camshafts,thats one of the reasons alot of people refer to the terms as lsa and ica-or intake centerline angle,its easier not to confuse the two terms.Vizard is correct,but the thing is it is very rare to get double digit power increses just from changing around the lsa/ica numbers on cams that are similar at .050,unless you were way out of the ball park to begin with.The more important aspect is overall performance of the vehicle and its intentions,which is the reason Vizard said there would be a "best" ica for the engine.Regarding the intake centerline Sherman racing and other builders alot of times simply advance the cams intake centerline until the highest cranking compression is achieved which is best for a strong low end and driveability as long as the overall compression ratio/gas quality is taken into consideration.Keep in mind when dealing with the ica advancing is lowering the power range and increasing cranking compression where as anything straight up or retarded is moving the power range up and decreasing cranking compression.Based on this its rather limited as to tailoring a cam with the ica alone since advanced is better for 90% of the engines out there and its adjustable if it isnt to specs.Thats why you should choose a cam based on the lsa for the given duration/power range,in my experience I run a 110 or a 108 for a n/a street engine depending on the stroke and duration as well as where I want the cam to operate,these seem to be the "sweet" lsa numbers.I also never try to crutch an engine by running excessive duration or a wide lsa since its always trading off performance and driveability,its best to have the right static compression to begin with.
This is what confuses most people on camshafts,thats one of the reasons alot of people refer to the terms as lsa and ica-or intake centerline angle,its easier not to confuse the two terms.Vizard is correct,but the thing is it is very rare to get double digit power increses just from changing around the lsa/ica numbers on cams that are similar at .050,unless you were way out of the ball park to begin with.The more important aspect is overall performance of the vehicle and its intentions,which is the reason Vizard said there would be a "best" ica for the engine.Regarding the intake centerline Sherman racing and other builders alot of times simply advance the cams intake centerline until the highest cranking compression is achieved which is best for a strong low end and driveability as long as the overall compression ratio/gas quality is taken into consideration.Keep in mind when dealing with the ica advancing is lowering the power range and increasing cranking compression where as anything straight up or retarded is moving the power range up and decreasing cranking compression.Based on this its rather limited as to tailoring a cam with the ica alone since advanced is better for 90% of the engines out there and its adjustable if it isnt to specs.Thats why you should choose a cam based on the lsa for the given duration/power range,in my experience I run a 110 or a 108 for a n/a street engine depending on the stroke and duration as well as where I want the cam to operate,these seem to be the "sweet" lsa numbers.I also never try to crutch an engine by running excessive duration or a wide lsa since its always trading off performance and driveability,its best to have the right static compression to begin with.
octanejunkie
Mopar Padawan
Hmmm, this statement starts out good, but a 108 cam for a 90% street driven vehicle is starting to get tight; trade offs will be idle quality, vacuum for accessories, piston to valve clearance, etc - but you will definitely increase cyl compression. I think Vizard's overpowering idea that there is 1 perfect cam (or at least LCA) for a given application is an interesting thought, but I am learning that a bit more lift can be more valuable and forgiving than too much duration. Obviously getting your compression (static and dynamic) in the proper range for your application and fuel is super critical - but it all boils down to a big picture equation, not just pick a cam that sounds good or idles a certain way - the trade offs are just too great. I do agree that 110 does seem like a street-able 'compromise' for the "I'm not sure what I want" crowd hence so many average cams are ground on 110-112
Would love to hear more experience and opinions on this one
lead69
hopeless car junkie
A 108 can be very streetable in an engine,its all relative to duration,stroke and cubic inches,now obviously this would be for a hot street/strip engine.I guess we have to differentiate between stock and h.p.,Im primarily talking about a strong,well tuned street/strip engine.As alot of engine builders do if you pick a cam and install it for max cranking psi you will make the most usable power from the cams starting power range on up and by design a 112 or wider is not advantageous to that,but it is a great application with forced induction,or to aid in tuning,or specific classes ect., ect.The science part is absolutely valid,but once again the average street/strip car would be hard pressed to pick up substaintial numbers by playing with the ica,so yes I would say its a big picture thing until you are running nascar ect.As long as the cam events are correct for the build the lsa can be quite different and not have a major effect on the peak h.p. number,just more where its at and where the power range is at.If your looking for mileage and smooth driveability you cant beat a 112 or 114 but personally I only consider them if max performance (n/a perfomance car) is secondary and duration is realatively mild for the displacement.
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