TheSamba.com :: View topic - Lobe Separation

Fri Aug 15, 2008 4:59 pm

Greetings -

In English, if possible, please help me understand:

1) What Lobe Separation means.
2) Why just a paltry few degrees more or less will affect performance.
3) How those paltry few degrees affect performance, up or down the RPM range.
4) Why I would order a cam other than 108 degrees of lobe separation

Thanks!

Mike

Fri Aug 15, 2008 5:42 pm

Quote: What is Camshaft Lobe Separation and how does it affect the engine?

Lobe separation is the distance (in camshaft degrees) that the intake and exhaust lobe centerlines (for a given cylinder) are spread apart. Lobe separation is a physical characteristic of the camshaft and cannot be changed without regrinding the lobes.

This separation determines where peak torque will occur within the engine's power range. Tight lobe separations (such as 106?) cause the peak torque to build early in basic RPM range of the cam. The torque will be concentrated, build quickly and peak out. Broader lobe separations (such as 112?) allow the torque to be spread over a broader portion of the basic RPM range and shows better power through the upper RPM.

question answered?

Fri Aug 15, 2008 5:43 pm

I just understand it from Hot Rod Magazine, Car Craft, Engine Masters Magazines.

Hope this helps. Personally, I'd like to see some of our resident VW guys do it. There are some pretty knowledgeable guys on here and it's interesting to see them write.

http://www.cranecams.com/?show=faq&id=2

http://www.compcams.com/Technical/FAQ/LSAproperties.asp

http://www.chevyhiperformance.com/techarticles/148_0307_basic_camshaft_info/index.html

Fri Aug 15, 2008 9:37 pm

Do not read the V8 engine articles and then use them in your decisions when building a VW engine. VW and V8 are two totally different engines and opperate under different circumstances.

Fri Aug 15, 2008 9:42 pm

Quote: 3) How those paltry few degrees affect performance, up or down the RPM range.

112 lobes as opposed to, say 108 lobes, *should* have a flatter torque curve. The torque curve of the 108 lobe cam, all other things being equal, will drop off sooner than the 112 lobe cam.

Fri Aug 15, 2008 11:03 pm

So far, I'm getting that the "lesser" separation is equivalent to power happening at "lesser" RPM. Is that right? Now, I'm trying to visualize why 2-3 degrees would make a noticeable, "feelable" difference.

Less degrees mean the exhaust will open x number of degrees (I'm talking 106 vs. 108) sooner. So why would that increase low-end torque?

Fri Aug 15, 2008 11:51 pm

Please understand, I'm a street driver that doesn't care one iota about 1/4 mile E.T.s. I want a low, wide, torque curve....

What I'm getting to is:

We usually choose a cam based on .050" duration and lift. The "lower" duration usually means "low end torque".

Lift isn't so cut-and-dried. You obviously (?) need more lift (flow) if you are going to run a stoker, than stock. It also has a lot to do with your springs, the "ramp", and so forth. Obviously (?), the less lift would lend itself to less stress on the valve train, due to an easier ramp.

Should we ("we" meaning the old farts that want street torque) pay more attention to separation than duration and lift? Obviously (?), it is going to be a combination of.... ALL THREE. Not just the duration/lift that is widely advertised.

In other word, let's say I'm looking to make tractor-like torque. I see a couple of cams that have similar duration/lift numbers. BUT, one has a 105 separation, and the other has (the "standard") 108:

1) Which one to choose?
2) Will it really make a "feelable" difference?

"Nite!

Sat Aug 16, 2008 12:02 am

Your really taking small differences in TQ and where it moves, by changing the lobe centre a couple of degrees you may on a 150ft/lbs of TQ engine move less than 10% of the TQ bt less that 500 rpm. I would just stick with choosing by 50@ numbers and lift.
The combo of inlet charge speed, head porting/chamber shape, compression ratio and exhaust size/scavenging if going to set you TQ curve.

Tell us about the vehicle and where you want power,post a chosen combo of parts so far and we will give opinions. :D

Sat Aug 16, 2008 12:28 am

Greetings K -

I see we're pulling the late shift. You have had valuable input to my other posts, and I thank you for that.

I am asking, in general, what the answers are. I really don't want to inject a particular vehicle into this. Asking for opinions only opens this up to the standard hi-po crap that I loathe.

Your numbers put torque 500 rpm "less", using a 106 (?) than a 108? Which is EXACTLY what I'm looking for.

But WHY? That is my question. I am looking for a technical explanation - not a recommendation.

Mike

Sat Aug 16, 2008 10:14 pm

I am asking, the 106 or 108 is how many degrees the exhaust opens... when..

1) after the intake closes?
2) after the intake opens?

So another question is.. Does the intake actually open a few degrees sooner?

Let's say 108 is "standard". If I get a 106, does that mean I get a cam with the intake 1 degree later, and the exhaust one degree sooner? Or the intake at the standard opening, and the exhaust 2 degrees sooner?

Thanks -

Sun Aug 17, 2008 12:33 am

LOL, not pulling a late shift look where I live.

The degree of separation is even from the center line, so as you said change the lobe sep numer by 2 degrees from 106 up to 108 and now opening is 1 degree earlier and closing 1 degree later. (to throw complication into this you can also not set the cam up straight, advancing or retarding it over the center line)
My example of numbers was not aimed to explain what will happen between a 106 and a 108, it was just trying to show the effects are small.
I went down the road you seem to be now of trying to grab every little degree I could to move the power band where I wanted it, but in the end its more complicated than just choosing numbers, there are some old threads on this if you search.
Have a look at the dyno graph for the CB engine, it makes TQ lower than my engine (smaller cam and exhaust) http://www.cbperformance.com/Mar2007.asp

:D

Sun Aug 17, 2008 2:18 am

And then there's the subject of VVT, where the intake cam is normally the one being constantly advanced or retarded (exception is the BWM double VANOS engine, of course), which effectively alters the lobe centerline between the 2 cams. :D