how to select lobe center, by DV

[theKbStockpiler]

If we read through these ; http://www.speedtalk.com/forum/viewtopic.php?f=1&t=45639&start=75

http://www.austincc.edu/wkibbe/camtheory.htm

http://www.hotrod.com/how-to/engine/0607phr-camshaft-basics/#photo-12

, it makes it clear that DV's last post of SpeedTalk is more or less a forum post and not a formal tutorial. I doubt if he posted anything it would not be assumed to be a tutorial.

From what I gather LSA is the absolute angle between lobe centerlines (separation) ,LCA is actually usually used out of context and refers to indexing the cam. As already stated the meaning is figured out by the context it is used in.
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[mark tucker]

modock I dissagree but thats normal.
also like all books there re written by somebody else befor going to the printer and many things change and get move around and some just plain rong. and then there is the vernacular, or syntax....no not sin tax. structure and that can affect how it is written and read. and if you choose to use the rong termanoligy but understand it right in your head ...that dosent work for somebody your talking to or they are reading it and think something different. so.....why not learn the right tremanoligy??? not many will understand it either way....
the stock piler seems to have the concept gathered up well. but wouldent it be nice if there were not all these dam abbrevations to confuzzie somenay people.....somany would still be confuzed any way, I will addmit after a long break from building somany big hp wild motors I have to think when reading this stuff to get them all straight in my head. and then there are those dam cam cards that dont list all the info you realy need&want on a cam card. as if it realy cost a lot to print that dam cam card.and then add the disclaimer"as designed" or as ground for the cams that come with a real cam card for that cam. are they too skeered somebody will check to see just how far off thier cams are??? Ive gotten oh so few cams that were what they said they were on a printed card, but the hand written card from that cam is always dead on, but never what the book says it is......but dam close. kinda like"guide lines"

[modok]

Ok, if the majority here votes for LSA, then I'll go with that. It's cool.
I will but a note in the first post to warn other readers that David is using the term "rong", and is aware of it, and does it anyway, just like me!
he says in part 2

"Study it for a while and you will see that a 108 Lobe Centerline Angle (also called a Lobe Separation Angle) for this particular engine (a 355 SBC with 186 heads and a 10/1 CR gave the widest and best output on a 108 LCA.

[ps2375]

wrong thread

[mark tucker]

I dont see lc as being the same as lca or lsa. but I reckon thats me. and I can live with that. sorta like the great seal of california....or how blue you were when singing the blues while the wind blew the smoke from when the motor blew.....crap that blows. somuch of the lingo is quite useless most of the time as 99% of us cant do anything about it . execpt for check and gess.

[theKbStockpiler]

LSA (Lobe Separation Angle) : The (difference) the intake lobe centerline is from the exhaust lobe centerline expressed in degrees. The lobes are Separated from each other stated in degrees of an angle.

LCA (Lobe Centerline Angle) seems to me to have to used in the context of what LSA means. 'Separation' is left out because every one should know that the exhaust and intake valves do not mirror each other in the same cylinder.

Why anyone would not just use the term 'index' is beyond me. 'I changed the relationship with the cam and crankshaft today by means of the timing chain'.I indexed the cam'

So if you are grinding a cam, LCA is the same as LSA. If you are installing a cam LCA is the same as phasing ,indexing or setting the relationship with the crank via the intake valve centerline or whatever.
_________________
My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask.

[bugguy1967]

[donnmon]

[bugguy1967]

1600 is 85.5x69

[modok]

[mark tucker]

Well what do ya know one size dosent fit all

[smkn_vw]

Should still work,

1600 cc / 4 = 400 cc
400 cc to ci = 24.41 ci
valve 39 mm = 1.53 in.

LCA = 128 - (24.41/1.53 x 0.91) = 113.5 deg.

I think the 0.91 is a correction factor to get you right to the LCA on the chart.

Why not just calculate the CID of valve diameter? Let the chart do the work for you but we'll have to disregard Dave's magic "128" number.
24.41/1.53 = 15.95
Go to left side of chart 15.95 and graph intersects at the same 113.5 LCA as above
It scales, it works.

Of course all of this is assuming CR of 10.5 Dave uses as baseline, Higher CR will add more degrees to LCA using his 0.6 correction factor.


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"So didja?" -Bob Hoover

[Boolean]

Methods like this are useful when you already KNOW what the numbers should be over a span of different configurations.
Vizard clearly has done his homework in regard to his engines, but ours are far outside his span.
Non linear, or even unscaleable methods may work well enough when the span is smallish.
I had a pet project once, measuring header diameter on factory high buck racecars where ever I could get to them.
The "formula" gives 50mm diameter per 500cc per 9000 rpm.
I would not expect this to work out on a moped though. Or at vastly different rpm's.
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Build thread here:
http://www.thesamba.com/vw/forum/viewtopic.php?t=529379

[mark tucker]

I dont think ours are far outside his span, more like he wasent addressing these engines when he was wrighten this. and if you disreguard any majick numbers you might as well throw away your smarter phone perhaps somebody should contact david and have him do some simulations for our motors. and have somebody translate it so us vw morons can read and comprehend it.

[smkn_vw]

I thought somewhere Dr. Dave mentioned his theory or formula works for motors with inline valves with 2 valves per cylinder. So it should apply to ours, right? I shouldn't say theory because he dyno tested to prove best LCA window.

I recall him mentioning optimal LCA is 108 degrees at 4 degrees advance.

Does this mean if I use his magic 128 formula and my "optimal" LCA comes out to 109 it's not my optimal and I should dial-in my cam 3 degrees advance?
_________________
"So didja?" -Bob Hoover