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Author Topic:   Lobe Seperation
Jerry Piner
Gearhead

Posts: 229
From: staunton, va
Registered: Dec 2001

posted 01-16-2002 10:58 AM     Click Here to See the Profile for Jerry Piner     Edit/Delete Message   Reply w/Quote
Excuse me for being dumb, but what exactely is lobe seperation and how does that effect how a cam works, and it's characteristics?

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capri man
Gearhead

Posts: 7611
From: doerun, ga.
Registered: Nov 2000

posted 01-16-2002 01:18 PM     Click Here to See the Profile for capri man   Click Here to Email capri man     Edit/Delete Message   Reply w/Quote
im glad you ask that question jerry!
answers anyone.

------------------
mike r
racing is real
everything else is just a game.
81 capri-7.56 @88mph 1/8
1.56 60 ft.

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Just Strokin
Gearhead

Posts: 754
From: Tuscaloosa, Alabama
Registered: Dec 2001

posted 01-16-2002 02:34 PM     Click Here to See the Profile for Just Strokin   Click Here to Email Just Strokin     Edit/Delete Message   Reply w/Quote
Lobe seperation is the number of degrees seperating the peak lift points of the intake and exhaust lobes at max lift. From what I have read, it is one of the buzz words that is easy to spout that most of us really have no idea what changing the lobe seperation encompasses.

If you change the overlap, you will change the lobe seperation which inturn affects cylinder filling by either forcing the mixture into the cylinder or using the exhaust gases to pull the incoming mixture. This inturn changes the idle characteristics, fuel economy or power, etc.

CompCams has some explained here.

And Crane say....

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?) allows the torque to be spread over a broader portion of the basic RPM range and shows better power through the upper RPM.

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SundanceKid
Gearhead

Posts: 1274
From: UT
Registered: Feb 2001

posted 01-16-2002 03:24 PM     Click Here to See the Profile for SundanceKid   Click Here to Email SundanceKid     Edit/Delete Message   Reply w/Quote
Yes it is the cam degree angle between the lobes at max lift. As was said above it effects the power band the lower numeric number the shorter more peaky the power band is the higher numeric number the longer the power band is spread through the rpm scale. It is the second most important value in cam selection. It has to do with intake reversion (large cams) and exhaust scavanging. Little more then a "buzz word" in my opinion.

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n2oMike
Gearhead

Posts: 2831
From: Spencer, WV
Registered: Jan 2001

posted 01-16-2002 05:00 PM     Click Here to See the Profile for n2oMike   Click Here to Email n2oMike     Edit/Delete Message   Reply w/Quote
Just a little tidbit I posted on another website when someone asked about lobe seperation... Thought some folks here might be able to use the info as well...

In a nutshell...

Decreasing lobe seperation:
1. narrows the powerband
2. moves the powerband lower
3. makes the idle choppier
4. makes more power
5. pumps up the midrange

Increasing lobe seperation
1. widens powerband
2. makes the idle smoother
3. takes away from the midrange
4. produces less maximum power

Racers usually use tight lobe seperations. The only exceptions are Pro-Stock, where 500+ ci are revved to the moon with cams so HUGE, tight LSA's produce too much overlap, and nitrous/blower/turbo applications where overlap sends all that extra fuel mixture out the tailpipe!

Tight lobe seperations increase overlap and can help increase velocity in overly huge intake ports (4bbl 351C). This will pump up the midrange, and make the engine feel less "lazy". Some 351C drag race cams have lobe seperations as low as 102-104 degrees. Automatics generally need a tighter lobe seperation for extra midrange.

Small engines with big ports LOVE tight lobe seperations, large engines with small ports work better with wider angles between the lobes.

A tighter lobe seperation also allows you to use a slightly larger cam in a lower rpm range. If you want maximum valve timing without revving the engine to the moon, a tighter lobe seperation can make it happen.

It's the dynamics of the tight (low) lobe seperation that produces the extra power.

Tightening the lobe seperation increases the cranking (effective) compression. The piston can only compress the air it traps in the cylinder. Long durations and wide lobe seperations push the intake closing event into the "compression" stroke. If air is escaping out the intake valve as the piston travels upward, it's not getting compressed, and cylinder pressure goes out the window! Narrowing the lobe seperation helps build more compression by making the intake valve close sooner, enabling the compression stroke to capture and compress more air. Advancing the camshaft will do this as well.

Some people mistakenly believe that compression is lost during the OVERLAP period... WRONG! Overlap occurs when the exhaust valve is closing and the intake is just starting to open... Nothing is being compressed yet! NARROWING the lobe seperation pulls the intake closing event out of the compression stroke. Advancing the cam will make the intake valve close sooner as well.

Here's another site with some lobe seperation info.

http://www.fordmuscle.com/archives/2001/04/camtech/

Just be sure to use an extremely free flowing exhaust with extra tight lobe seperation angles. Their scavenging effect from their extra overlap NEEDS some free flowing tubes, or the exhaust will just get backed up into the cylinders... Really bad exhaust systems will actually make the carburetor get all black with carbon. Open er' up, and let er' fly! I really like the dual 3" woofers that occupy the underside of my car.

Also ask yourself how high you are willing to rev the engine before deciding upon a camshaft.

Good Luck!

------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/carbedstangs/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367

[This message has been edited by n2oMike (edited 01-16-2002).]

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