Some concepts are getting mangled here. The timing of the vlave events is why the LSA is important. You can't say one is more important than the other as they are dependent on each other. If you have the same lobes and you change the LSA, you change the timing of the valve events and vice versa. If you advance or retard the cam, you can change the valve timing without changing the LSA, but you can't do the opposite (change LSA without effecting valve timing) - so it makes no sense to debate "which is more important, LSA or valve timing."

That said, I agree that most off-the-shelf street grinds have too wide an LSA for optimum power.

Rich

 

Very true(IMO)......107's and 108's work great on the bottle up to a certain point of nitrous HP increase......In my experience(not that it means everything ), things are pretty even as far as gains (tight VS wider LSA's) untill you go above 250 shots(or so)...it then seems that the pumping losses are starting to hurt a little with the real tight LSA cams.............Joe

 

"Get into the habit of recognizing open/close points".

The LSA has ALL to do with opening/closing points as does ramp rate,duration,and lift.As does ICL.
BTW Rich IS THE DOCTOR.

 

LOL! He teaches other MD's also.

 

How many lives are saved EACH year by the medical profession? I don't have hard numbers, but my wild guess is that it exceeds 100,000. Could it be 1,000,000 or 10,000,000?

I strongly agree with you that some folks are better qualified than others...to cut and paste on a human body or to choose a cam. Aren't you just making my point for me?

I'll continue to urge forks to see an MD when they have serious medical problems/trauma, and a cam professional when they want good cam advice rather than self-perscribe. In my family we have both a medical professional and a cam person. I see their results on a daily basis. I also see the results of self-medication and DIY cam design on a regular basis. That prompted my advice.

FWIW, many folks consider the cam (valve events) to be the "brain" of the engine, so I'll revise my analogy to add "DIY brain surgery".

 

As you and many other professional and non-professional people have said the LSA is a result or effect of selecting valve events.

Probably the easiest way to order a cam is to use the lobe profile numbers for intake and exhaust lobes, state the LSA or angle in cam degrees between the centerlines of the intake and exhaust lobes and any built in advance or retard wanted. Unfortunatley many folks jump right to the LSA as being an important design number.

IMO, David Vizard uses LSA in his writing in order to reach/teach a larger audience than if he just used valve events. He does explain LSA's relationship to the valve events, but I think he may lose many readers if he doesn't continually relate things to LSA or LCA. The good thing is that he preaches LSAs in the range that make good/best power rather than the "safe" ones shelf grinds often have.

Each engine/vehicle combination may have one best set of valve events. (IVO, IVC, EVO, EVC) If you knew what they are, you automatically know the durations and the resulting LSA. If a person knows how to determine those "best" valve events accurately they are a "pro" even if they don't sell their knowledge or cams for a living.

Conversely, if one doesn't know how to determine the "best" valve events, they should let someone else do the job. Of course you should choose your "pro" carefully..whether it be cam design or medicine. The rub comes from deciding who you should choose. If you are involved in the "profession" you have a pretty good idea of who does what well...or poorly. Otherwise, results and reputation are about all you can go on. That works both in medicine, where practioners are licensed and monitored, and in engne building where they are not.

My $.02 both on and off topic.

 

Cause,who said anything about a "cause"
What kind of cause "Green Peace"

Were we not talking LSA here?

The LSA has ALL to do with opening/closing points as does ramp rate,duration,and lift.As does ICL.

 

would a cam have a better lope with a 110 lsa or a 114 lsa????

 

Don't know about better,but a 110 would have the bigger lope,less vacuum,less low end by a tad.

 

Thanks for the info. I have a 110 Lsa cam for my 383.

 

Don't you just hate HMOs? Especially the ones which hire "Medical Dieties" rather than real docs (like Rich).


Some (non-self appointed) cam pros actually do answer the questions and post the answers on forums like this. Unfortunately, as evidenced by this thread, many of the folks who need to understand what you, I and others continue to say about LSA and valve events aren't listening...or perhaps it is that they just are not understanding.

What is the saying about "preaching to the choir"?

There is another old teacher's bromide which fits the situation...

Oh yeah, "Doctor".

 

OldSStroker
Are you saying that if a maxed out lobe profile,maxed in ramp rate,velocity and lift, are used in a 108*LSA then ya put the same profile on a 116LSA that ya don't get less overlap or ya do?
The only way I see to have less overlap with a narrow LSA(108) is with an inverted radius cam that WON'T live very long on the street.
LSA changes the valve opening/closing point or vice-a- versa on a normal cam. To me ya can't take a given ramp on the opening side then drop the valve off a cliff on the closing side to meet your desired closing point.

 

No, I don't believe I said that.

Maybe what I said was that a given engine combination wants the four cam events at certain points. That pretty much determines duration as well as overlap. I guess that means you pick (or design) a lobe with the duration the valve events want, the aggressiveness you can stand and the rocker ratios available to you. If the lobes are fairly symmetrical, you arrive at a LCA or Lobe Centerline Angle.

Take an example:

A certain V8 design liked these valve events (seat-to-seat):

IVO 23 BTDC
IVC 64 ABDC

EVO 68 BBDC
EVC 29 ATDC

Therefore:

INTAKE DURATION = 267 DEGREES
EXHAUST DURATION = 277 DEGREES

From valve events, the calculated LCA = 110 degrees and the overlap is 52 degrees

It also liked about .560 intake and .600 exhaust valve lift with a hydraulic roller and 1.6 RAR. It liked an intake lobe area arroud 25 inch*deg and an exhaust lobe area around 28 inch*deg.

It wasn't all that difficult to find lobes which gave those results. Therefore the cam was spec'd as a XXXX intake lobe and a YYYY exhaust lobe ground on 110 degree LCA straight up +/- 1/2 degree. This was determined by valve events, not some arbitrary LCA (or LSA in "forum speak").

I believe you can "drop the closing side off a cliff" if you do things exactly right and get it to live for at least the time you plan to race it. A typical Cup engine runs 1.5 to 2.2 million revs in anger on a race weekend. If that's your bogey (with a safety factor added), you might be able to get a way with some wild lobes. If you want to run 25 million revs (maybe 10000 miles), you need to be less aggressive, I agree. If you want to last 250-500 million revs (OEM) you need to back off the aggresivness and/or upgrade the components.

 

Won't the valve closing point determine the RPM that the HP/TQ peaks.
The older Pro Stocks were running an LSA of 120+ with a 12+degrees of advance.
They won't even pull up into the driveway off the street without revving them to 5000 and burning the clutch(they were not designed for such)


I think most on the board want it to last 100,000 miles and don't care about 25million rev's to failure

Me I like "in rad cams" but ya got to rebuild the heads and valve train 3-4 times a year. Boy do they make HP. Dave Crower is the only one who will build me any and I have had the lecture more than once 'bout don't blame him ta da ta da.

Believe it was A/G that said ya could have less overlap with a narrower LSA/LCA
Don't see how, as for a pyramid type lobe profile like I said ya can't just drop the closing side off a cliff unless it's an inverted radius cam.
I too use valve open/closing points to get there but I still let Dave tell me what he thinks and I go too big most of the time('60's) and he keeps telling me the profiles have changed so I am slowly changing my mind set also.

 

This talk of "dropping off a cliff" would entail a cam who's lobe ramp angles are a-symmetrical to either side of the LCA...right?