Can someone please explain to me why it is best to use a camshaft with a 114 LSA with the rams horns manifolds and stock heads rather than a camshaft with a 112, 110 etc LSA??

THanks

 

My understanding is that the 114 lobe seperation has less overlap (where both intake and exhaust valves are open at the same time). With a restrictive exhaust like ramshorns, the exhaust gas can try to re-enter the cylinder and so dilute the incoming air/fuel if the overlap is too great.

 

That makes since, but i guess that all depends on duration as well.

The 327/350 cam probably doesnt have much overlap if any, but i would guess that the 327/365hp cam had a good bit of overlap with the 254 duration.

 

The recommendation is based on reducing the overlap, biased as a compromise with the late closing of the intake valve on the compression stroke.

The (116) 114 LCA recommendation is ONLY for the GM solid lifter cams (the LT1 & 30-30). The reason is that with the soft (mild-intensity) GM lobe ramps there is considerable (long) duration that requires the LCA to be widened to minimize the valve overlap.

Use a shorter duration cam, or one with a higher intensity, and the LCA can be narrowed to achieve nearly the same overlap. This is how a LCA of 110, like that with the Duntov-097' cam, can have similar overlap to the LT1 cam. Use a high-intensity lobe, like a modern Isky, Crower, Crane, Lunati, (etc.) and you can have a similar 0.050 duration (sometimes more 0.050 duration) with a tighter LCA and achieve less overlap (one of the advantages of modern grinds, and rollers).

Overlap is not measured in LCA, or even overlap degrees of cam duration. Overlap is measured in square-inch-degrees of open valve window area. A head with larger valves with have more overlap than a head with small valves, even with the same cam.

A modeling program like the EA3.2 comes with a book (the "help" manual) that will explain the differences between overlap, LCA, duration, duration at different lifts, and Inlet valve closing angle. All of these factors (and a few more) help predict how a cam will perform.

It's not a simple answer, because choosing from the GM cams is a compromise (compared to everything learned since the late 60's).

Good Luck!

 

Thanks! Do you now if the Desktop Dyno 5 is any good?