Lobe Separation for Speed Density Cams

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Apr 12, 2024 | 08:43 PM

#16

nitromaster

4wd Low

Joined: Feb 2024

Posts: 10

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ok, so you're saying i could theoretically run a 110 lobe separation on speed density, but "only" if the durations are around .220 @ .050?
Or would having 110 separation in general be too unstable?

Apr 12, 2024 | 10:41 PM

#17

rwfid

Mountain Pass

Joined: Feb 2017

Posts: 182

Likes: 58

From: Kentucky

You can always go with an aftermarket ECU if you can't get it to run right on the factory speed density. It might be a little more than you want to spend, but the sky is the limit.

Apr 23, 2024 | 07:53 PM

#18

Conanski

FTE Legend

Joined: Jun 2006

Posts: 31,930

Likes: 1,499

From: Ottawa, Ontario

Quote:

Originally Posted by nitromaster

ok, so you're saying i could theoretically run a 110 lobe separation on speed density, but "only" if the durations are around .220 @ .050?

The manifold vacuum signal has to be stock like, in my experience to have any hope of doing that the cam intake duration has to be 210 deg@0.050" lift or less even with 114deg LSA, with 110deg LSA I'd bet it needs to be under 200 degrees.

Apr 23, 2024 | 08:37 PM

#19

DaveMcLain

Cargo Master

Joined: Oct 2020

Posts: 2,675

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That's right, for the most part it is the overlap that reduces the manifold vacuum at idle which is what the speed density system doesn't like. The lobe separation controls the overlap along with the duration. If the durations are kept the same for the most part changing the LSA will change the overlap by about 2X the change. So in other words going from 114 down to 110 doesn't change the amount of overlap 4 degrees it changes it 8 degrees which is a lot. The reason I say for the most part is because all lobes are not symmetrical so it can vary a little bit.

The Non HO 5.0 camshaft (the one with the std 302 firing order) checks at 181/195 @ .050 and it is ground on a 108 lobe separation. It has .379 and .395 lift with a 1.6 ratio rocker arm. It has 33 degrees of overlap at .006 cam lift, 19 degrees at .010 and 1.3 degrees at .020.