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TorkMonster400 09-18-2008 08:15 PM

Cam lobe seperation
 
I was looking at my cam card a few minutes ago, while updating my journal and I noticed something strange.
In the Lobe Center section it says 112+4 I have never seen this and it may be a dumb question but what is the +4 mean? can anyone help :confused:

automotive breath 09-18-2008 08:22 PM

I'm not sure but I think it means the lobe separation is 112 and the intake lobe
is ground in the 4 degrees advanced position (108 lobe centerline).

TorkMonster400 09-18-2008 08:48 PM

2 Attachment(s)
Here is a scan of the card

sam-missle 09-18-2008 10:26 PM

As Automotive Breath said, 4 degrees advance, most flat tappet cams are ground 4 deg. advanced. very few company's show it on the cam card.

sam-missle

TorkMonster400 09-19-2008 12:13 AM

Thank you for the help guys. :thumbup:

454C10 09-19-2008 09:25 AM

I believe that means it is an asymmetric cam. That means the lift ramps and lowering ramps are not the same. So, the max lift is not centered on the lobe profile.

If you do the math on the @0.050" then the LSA should be 112 degrees if the max lift is centered on each. On asymmetric cams, typically the exhaust closing ramp and the intake lift ramp is slightly slower, so it spreads out the peak to peak lift point (exhaust peak and intake peak).

So, even through the LSA is 112, centered between the closing and opening points, it will be 116 (112+4) at the peaks which is the typical way to measure LSA.

so install the cam at 112 degrees at the intake peak.

automotive breath 09-19-2008 11:20 AM

454C10, I have never seen anyone refer to the lobe ramps when discussing
lobe separation, what I have seen goes off of lobe centerline.


http://images.chevyhiperformance.com...mage_large.jpg

454C10 09-19-2008 12:02 PM

The lobe centerline and the lobe peak lift is typically the same (as in your diagram). But not in asymmetric cams where there the opening ramp is different than the closing ramp which puts the peak lift off center.

ScoTFrenzel 09-21-2008 12:03 AM

Peak is peak. LSA is always given as peak to peak.

When cams are ground with say +4* advance, both the intake and exhaust lobes are ground with that 4* advance.
In simple terms = the whole cam is advanced, not just the intake lobes.
All they are doing is moving the cam "keyway/dowell" so the entire cam is advanced.

baddbob 09-21-2008 07:34 AM

The ground in advance is to make up for the eventual timing chain stretch from what I've been told.

Stroke 09-21-2008 10:49 AM

The cam is described as 'hot street', which advance ground in would be right for that description. Advancing for street use is the norm. I'd call Howard's to be sure, but you should simply install this one straight up as opposed to advancing. JMO

ScoTFrenzel 09-21-2008 10:57 AM

The 4* ground-in advance is to help those guys who don't degree a cam, and just stab it in with a stock type one-key-way gear set.

Sometimes due to parts variation the ground-in advance helps when using a 3 keyway gear set by allowing you to gain a little additional advance for variation adjustment and for future chain stretch.

If you are degreeing in a cam with a proper degree wheel, etc. then where the cam is actually ground is irrelavent.

Decades of experience has taught cam grinders and users that MOST combinations will produce more power and "feel better" when the cam is installed about 4* advanced.

454C10 09-21-2008 01:54 PM

compcam said they advance their street cam 4 degrees because most people buy cams too big.


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