lobe separation angle

-
This diagram should explain it.
 

Attachments

  • image.jpg
    15.4 KB · Views: 906
Breadburner said:
108 sounds real nice....
Click to expand...

Oh that helped out a lot.


Wider LSAs tend to give a broader and flatter torque curve, with good street manners, a strong vacuum signal and a smoother idle.

A narrower LSA gives more peak torque at the expense of bottom end torque in comparison. Also diminished street manners and a lower vacuum and rougher idle.

All that said, you will likely not see much difference between a 110 and 112 LSA, all other specs being equal or close to it.

Generally speaking, everyday street engines work better with a wide LSA, while hotter street/strip engines work better with a narrow LSA. This is why you see the factory Chrysler cams like the Road Runner cam and the 340 cams were ground on a 115 and 114 LSA respectively.

No one can argue that they did not perform, either.
 
so less valve overlap preserves compression on wide lsa
..better bottom end a little less high rpm capability?
opposite for a narrower lsa
..a little less dynamic compression,a bit more high rpm hp?
 
ir3333 said:
so less valve overlap preserves compression on wide lsa
..better bottom end a little less high rpm capability?
opposite for a narrower lsa
..a little less dynamic compression,a bit more high rpm hp?
Click to expand...


Yes, that's another way to look at it.

Wider LSA gives less overlap and better low end power...

Narrower LSA gives more overlap and more top end and sacrifice some bottom end...
 
RustyRatRod said:
Oh that helped out a lot.


Wider LSAs tend to give a broader and flatter torque curve, with good street manners, a strong vacuum signal and a smoother idle.

A narrower LSA gives more peak torque at the expense of bottom end torque in comparison. Also diminished street manners and a lower vacuum and rougher idle.

All that said, you will likely not see much difference between a 110 and 112 LSA, all other specs being equal or close to it.

Generally speaking, everyday street engines work better with a wide LSA, while hotter street/strip engines work better with a narrow LSA. This is why you see the factory Chrysler cams like the Road Runner cam and the 340 cams were ground on a 115 and 114 LSA respectively.

No one can argue that they did not perform, either.
Click to expand...

Thanks. Nice explanation.
 
LSA has VERY little to do with compression the engine will create.

When the intake valve closes has a greater effect on compression.

Put a 114 lsa cam straight up in the same engine as a 106 lsa straight up, the 106 will thrash all over the bottom end power of the 114.
 
crackedback said:
LSA has VERY little to do with compression the engine will create.

When the intake valve closes has a greater effect on compression.

Put a 114 lsa cam straight up in the same engine as a 106 lsa straight up, the 106 will thrash all over the bottom end power of the 114.
Click to expand...

Ya think? I would like to see it. Everything I have read as well as experienced says otherwise......as long as everything elses stays the same.
 
Pick a cam, any wide LDA cam.
When you tighten up the LDA of that same cam, You will be closing the intake earlier.
The overlap difference will be exactly double the LDA change and;If you put them both in exactly at split overlap,the ICA will be exactly 1/2 the overlap difference.
By tightening up the LDA you will be getting an earlier closing intake valve(and more Dcr), and a longer power extraction cycle, and as a consequence; more overlap.
More power extraction is not always better, unless you are going for gas mileage. Most of the work of the expanding gas is done by 90 to 100 degrees ATDC
More overlap is not always a good thing either, especially with log manifolds. But with tuned headers, this period can be exploited.

Lets pick a pair of 276/284 cams, one is 114, and the other is 108.
Lets start with the 114 cam. To put it in at split overlap requires an installed centerline of 112. Then the Intake will close at 70*ABDC, leaving 110* for compression.Power extraction will be 102*. And overlap will be 52degrees.
Next, lets check the 108LDA. To put it in at split overlap, requires an installed centerline of 106*.The intake will close at 64*ABDC, leaving 116* for compression. Power extraction will be 108*, and overlap will be 64 degrees.

Let's say you have a 30over-teener with a true 10.0 Scr. According to the Wallace Calculator;
The 114 cam, in at 112, will make a 7.58 Dcr@ 148 cranking compression.
The 108 cam, in at 106, will make a 7.96 Dcr@158 cranking psi

Running characteristics are mentioned above.It is my opinion that as specific power increases on those narrow-LDA cams,the powerband decreases; meaning they become more sensitive to what tranny runs behind them, and what rear gear it is stuck with.Maybe sensitive is the wrong word. The power comes on later and harder. So if you are stuck with bad gearing, the power delivery won't really start until you are way speeding. This is probably not a concern for most streeters with typical street cams.
I can tell you from experience that the 292/508/108 cam likes plenty of rear gear to get going, and likes at least a 4 speed, or if an auto, likes plenty of TC.In my combo it kinda exploded at 5500 and carried on to past 7000. So that was a 1500 rpm powerband.But with 3.55s it didn't start until 64mph. See what I mean?
Now the Hughes 230*/110LDA cam I currently have, is very similar to that 276/284 cam. The engine has a totally different character. The powerband seems to start at 3500 to 4000, but it is incredibly long and flat. I can't really feel it come on, like I did the Purple.At first I was very disappointed.But after some retuning, it's kinda nice putting the hammer down at 3500/41mph, and lighting up the 295s. I kinda miss the nasty 292 idle tho....
Now here's the kicker; the 292,in at 104 has an ICA of 70*ABDC, which would be the same as the above 276/114 cam, and just 6* later than the current 276/110 cam. The rest of that duration was moved into the overlap period.Totally different character.The idle vacuum was quite a bit lower, and the peak-vacuum rpm was quite a bit higher. I don't recall the numbers anymore, but estimating, I would say the 292 idled 3 to 4 inches lower and vacuum-peaked 500 to 600rpm higher.No biggy,a little more gear for the 292, and a little more clutch, and away it went. Then when it hit 5000, hang on! Then, keep it on the pipe...
 
crackedback said:
LSA has VERY little to do with compression the engine will create.

When the intake valve closes has a greater effect on compression.

Put a 114 lsa cam straight up in the same engine as a 106 lsa straight up, the 106 will thrash all over the bottom end power of the 114.
Click to expand...

While I agree 100%, I feel the comment is misleading without a lot more info. LSA taken by itself, and it's affect on any engine's power curve means very little unless you know a lot more about that given combo.
 
krazykuda said:
Yes, that's another way to look at it.

Wider LSA gives less overlap and better low end power...

Narrower LSA gives more overlap and more top end and sacrifice some bottom end...
Click to expand...


Little backwards..........wide lsa more top end power and wider power curve, tight lsa more torque down low and peakier narrower power band.......
 
The wider lobe separation angle closes the intake valve later and reduces cylinder pressure, so that is where it's detonation resistance comes from. Really wide lobe separation angles are used in boosted applications. Many later model engines use wide lobe separation angles to reduce overlap for idle quality and fuel economy.


The only reason I use a wider lobe separation angle is to smooth out the idle and increase idle vacuum.

[ame]http://www.cranecams.com.au/pdfs/MAY14-Lobe_separation_article.pdf[/ame]
 
ir3333 said:
how does 110 compare to 112 and why?
haven't quite got a grip on this...
Click to expand...

Is this a therotical question, or do you have a hard combination you are thinking about? Situations ( strokers /blowers/nitrous/turboed/..),,
 
just trying to figure this out to build a decent "Teener"
...i'm more confused than ever now!
 
The question is similar to asking what the difference between two whites is without showing us the actual paint chips. What do you have, and what are you looking to accomplish? The more specific you are, the better anyone can help you.
 
i have built a few 340's and no denying a mild 340 is a perfect fit for a well balanced all around performance A body street machine.Not too much torque,excellent launch,quick revving,good mileage and pulls hard from 1200 to 5200 rpm...
But...i think my next project will be a Teener so i'm trying to figure out exactly the best all purpose combination...with an emphasis on silky smooth idle,good torque,handling and mileage...
 
You must log in or register to reply here.
-

Back
Top