[kleetuz]

How do larger and smaller lobe seperations effect the power range in an engine?

I am looking at some crane cams and on their spec cards I can't find the LSA anywhere, is there anyway to calculate this from the other numbers for the cam?

 

[Wurf]

Wider lobe seperation enhances low end torque. Closer lobe seperation helps evacuate the cylinder due to increased overlap. The amount of lobe seperation you need depends on the application. Turbo or blower? 351, 302? What do you have and what are you doing?

 

[kleetuz]

351C
It is all stock except for a mallory ignition. The car has 3.50 gears, no-slip diff, and a 4 speed manual tranny, OEM Holley 650cfm Carb.

I have acquired 2V aussie heads and am going to have hardened seats put in, new valves, etc. But this is going to wait until I have all the parts for the cam- springs, retainers, lifters etc, and I also want to run roller rockers on the heads. I am going to put on a Weiand 2V X-cellerator intake.

The cam I want to get is Crane #52442
Intake/Exhaust: Advertised Duration 288°/292°, Duration @ .050” 236°/230°. Lift: .528”/.536”

I was wondering what lobe seperation this cam has because the spec card online doesn't say. That way I can look around and compare and really figure out if I want a big seperation or small before I get it. Somehow I think that it is a 114 degree LSA but that's pretty big...

 

[Mach1Morgan]

That Crane Cam has a lobe seperation of 110 degrees and is ground with 5 degrees of advance. Therefore your intake lobe centerline will be at 105 degrees ATDC and your exhaust lobe centerline angle will be at 115 BTDC. You'll have to run a set of long tube headers and a good free flowing exhaust system for best results with that cam, but it's a good cam for use with 2V Clevelands heads.

 

[85mike]

The 4-speed is a little more forgiving in the cam department. Should work fine.

 

[n2omike]

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, as do engines limited to smaller sized carbs and/or intakes.

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.

Good Luck!

_________________
Mike Burch, 66 mustang real street
302 4-speed 289 heads, 10.63 @ 129.3
http://www.mustangworks.com/cgi-bin/moi-display.cgi?220
http://www.fortunecity.com/silverstone/healey/367

<font size=-1>[ This Message was edited by: n2omike on 6/24/04 11:09pm ]</font>

 

[107543]

N2O mike...so the racing cams w/ low lobe separation must have high lift right? just trying to understand it all!

 

[n2omike]

No, low lobe seperation does not dictate high lifts. 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.

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

<font size=-1>[ This Message was edited by: n2omike on 1/9/02 1:05pm ]</font>

 

[67stang]

read this too:
http://www.fordmuscle.com/archives/2001/04/camtech/

 

[n2omike]

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.

Good Luck!