Lobe Center

Venom S · #1 (**permalink**) 12-17-2002, 01:26 PM

Can someone explain what lobe center is?

Thanks

Venom_S

Mr.Fixit · #2 (**permalink**) 12-17-2002, 01:32 PM

The number of camshaft degrees of rotation between the middle of the intake lobe and the exhaust lobe. A small lobe center, say 108 leaves the exhaust valve open as the intake is starting to open, more than say the same cam with a lobe center of 112.

scottj · #3 (**permalink**) 12-17-2002, 01:40 PM

The intake valve reaches its maximum lift at some defined point after top dead center. This is refered to as the intake centerline, which refers to where the cam has been installed in the engine in relation to the crankshaft.

Venom S · #4 (**permalink**) 12-17-2002, 01:44 PM

If I understand you correctly, Mr. Fixit, then a cam with 108 would be more radical at idle than one with 112 degrees?

Venom_S

scottj · #5 (**permalink**) 12-17-2002, 02:12 PM

Venom_S- Typically a cam with less lobe separation (lobe center) will have more overlap and poorer idle quality.-Scott

Ron61 · #6 (**permalink**) 12-17-2002, 02:20 PM

Venom_S

The best book that I have found is the Desktop Dyno book from Motion Software. It does a great job of explaning lobe seperation and overlap complete with pictures and graphs. I never could get that stuff straight until I got that book. Now I almost understand it.

Junket · #7 (**permalink**) 12-17-2002, 02:25 PM

OK V.S let see if I can get this out. The lobe-seperation angle determines the relative phasing between the ex. lobe --the ex. event---& the intake lobe the intake events.(the over lap) The engine that has smaller lobe-seperation breath better at higher RPM more top-end HP & less lower end torque. The greater seperation angle better low-end breathing more low-end torgue.This is why some advance & tetard the cams & some run differnt rocker ratios on some motors this screws with the lobe separation.
Ken

Venom S · #8 (**permalink**) 12-17-2002, 02:26 PM

Thanks

I am looking at several hydraulic flat tappet cams to put into my 500 cubic inch BBF. Here is what I have found:

Comp Cams
.585/.585 lift, 253/253 deg dur @ .050 lift, 110 lobe sep

Crane Cams
.599/.599 lift, 248/248 deg dur @ .050 lift, 108 lobe sep

Edelbrock Torker II cam
.556/.581 lift, 234/244 deg dur @ .050 lift, 108 lobe sep

Ford Racing
.588/.614 lift, 244/254 deg dur @ .050 lift, 106/114 lobe center

Any recomendations?

Venom_S

Mr.Fixit · #9 (**permalink**) 12-17-2002, 02:28 PM

Don't confuse "lobe center" with "intake lobe centerline"

Lobe center is ground into the cam, it cannot change unless you buy another cam

Intake lobe centerline is how far advanced or retarded the cam is installed.

Junket · #10 (**permalink**) 12-17-2002, 02:44 PM

This is what I would BAR none spend a few more $$$$ on a Desktop Dyno and plug all the equations in and play you can see where the power band is on each cam because the same cam will be different in a 390" motor than a 500" motor ( you could have a ***** cat in one and a tiger in the other.)not only it is a fun toy if you are in to that stuff.
Ken

Venom S · #11 (**permalink**) 12-17-2002, 02:49 PM

Junket

EXCELLENT IDEA!! My short block, heads, and carb are already set.

Thanks a lot

Venom_S

Hotfingrs · #12 (**permalink**) 12-17-2002, 02:58 PM

Also the smaller the lobe center, the narrower the power band

scottj · #13 (**permalink**) 12-17-2002, 02:59 PM

In fact there was so much confusion between int. centerline and lobe center, that "lobe center" has just about been eliminated from cam terminology, having been replaced by the term "lobe separation"

Junket · #14 (**permalink**) 12-17-2002, 03:00 PM

Good Venom_S now that we talked you into spending some more $$ on the toy

have read some reports that most of the desktop dynos are suprising good 10% 18% what they are on the real stuff.

Ken

Venom S · #15 (**permalink**) 12-17-2002, 03:03 PM

Do you mean they are understating or overstating real horsepower?

Venom_S

Junket · #16 (**permalink**) 12-17-2002, 03:08 PM

Could be either way to many varables hot cold good air bad air.

Venom S · #17 (**permalink**) 12-17-2002, 03:18 PM

Given the fact that the software is simply a modeling tool, it should still be helpful in determining the best cam for my engine, correct??

Venom_S

Junket · #18 (**permalink**) 12-17-2002, 03:38 PM

That is correct that is the best way to explain it.

jdean · #19 (**permalink**) 12-17-2002, 05:44 PM

I have the Desktop Dyno from motion, and not only are cams explained well, but so are headers etc.

Of couse the best cam for your engine is the one that makes it behave closest to your own personal ideas of engine performance. Top end strong (racing) vs. low end torque (street) etc., or the best compromise of the two.

An example, since I will run an automatic, with not a huge interest in the track, my cam selection was more mid-range torque heavy than the grinds you mentioned based on the Dyno model.

Excaliber · #20 (**permalink**) 12-17-2002, 07:06 PM

Hmmmm,,,,,less lift would be easier on the valve train. Less lift: A smaller number lobe separation cam could make up for that AND save the valve train! Maybe thats the way to go if your building an "endurance" motor that runs in a specified rpm range most of the time (500 mile NASCAR race I'm thinking). Camshaft profiling, cool stuff!

Ernie